CA2619778C

CA2619778C - Method and apparatus for sequencing transactions globally in a distributed database cluster with collision monitoring

Info

Publication number: CA2619778C
Application number: CA2619778A
Authority: CA
Inventors: Frankie Wong; Xiong Yu; Elaine Wang
Original assignee: Open Invention Network LLC
Current assignee: Open Invention Network LLC
Priority date: 2005-09-09
Filing date: 2006-09-08
Publication date: 2016-08-02
Anticipated expiration: 2026-09-08
Also published as: CA2619778A1; WO2007028249A1

Abstract

A system and method for duplicating a plurality of transactions for a primary database received from at least one application over a network as a plurality of replicated transactions for a secondary database. The system comprises a status module for monitoring a completion status of each of the plurality of transactions received by the primary database, such that the completion status indicates a respective transaction of the plurality of transactions has been successfully processed by the primary database. The system comprises a global queue for storing each of the plurality of transactions for facilitating the transaction duplication in a selected transaction sequence order, wherein the global queue is configured for storing the plurality of transactions and the respective completion status of each of the plurality of transactions including a respective transaction identification. The respective transaction identification represents a unique sequence identification for each stored transaction of the plurality of transactions. The system comprises a controller module coupled to the global queue and configured for assigning the respective transaction identification to each of the plurality of transactions and further configured for duplicating as the plurality of replicated transactions all of the transactions with a successful completion status of the plurality of transactions for storage in a replication queue for facilitating transmission of the plurality of replicated transactions to the secondary database for processing.

Description

, METHOD AND APPARATUS FOR SEQUENCING TRANSACTIONS
GLOBALLY IN A DISTRIBUTED DATABASE CLUSTER WITH COLLISION
MONITORING
FIELD OF THE INVENTION
[0001 ] This invention relates generally to the sequencing and processing of transactions within a cluster of replicated databases.
BACKGROUND OF THE INVENTION

[0002] A database has become the core component of most computer application software nowadays. Typically application software makes use of a single or multiple databases as repositories of data (content) required by the application to function properly. The application's operational efficiency and availability is greatly dependent on the performance and availability of these database(s), which can be measured by two metrics: (1) request response time; and (2) transaction throughput.

[0003] There are several techniques for improving application efficiency based on these two metrics: (1) Vertical scale up of computer hardware supporting the application - this is achieved by adding to or replacing existing hardware with faster central processing units (CPUs), random access memory (RAM), disk adapters / controllers, and network; and (2) Horizontal scale out (clustering) of computer hardware supporting the application - this approach refers to connecting additional computing hardware to the existing configuration by interconnecting them with a fast network. Although both approaches can address the need of reducing request response time and increase transaction throughput, the scale out approach can offer higher efficiency at lower costs, thus driving most new implementations into clustering architecture.

[0004] The clustering of applications can be achieved readily by running the application software on multiple, interconnected application servers that facilitate the execution of the application software and provide hardware redundancy for high availability, with the application software actively processing requests concurrently.

However current database clustering technologies cannot provide the level of availability and redundancy in a similar active-active configuration.
Consequently database servers are primarily configured as active-standby, meaning that one of the computer systems in the cluster does not process application request until a failover occurs. Active-standby configuration wastes system resources, extends the windows of unavailability and increases the chance of data loss.

[0005] To cluster multiple database servers in an active-active configuration, one technical challenge is to resolve update conflict. An update conflict refers to two or more database servers updating the same record in the databases that they manage.
Since data in these databases must be consistent among them in order to scale out for performance and achieve high availability, the conflict must be resolved.
Currently there are two different schemes of conflict resolution: (1) time based resolution; and (2) location based resolution. However, neither conflict resolution schemes can be enforced without some heuristic decision to be made by human intervention. It is not possible to determine these heuristic decision rules unless there is a thorough understanding of the application software business rules and their implications.
Consequently, most clustered database configurations adopt the active-standby model, and fail to achieve high performance and availability at the same time. There is a need for providing a database management system that uses an active-active configuration and substantially reduces the possibility of update conflicts that may occur when two or more databases attempt to update a record at the same time. Further, it is recognized that collisions between two or more concurrent transactions in a selected database needs to be addressed.

[0006] The systems and methods disclosed herein provide a system for globally managing transaction requests to one or more database servers and to obviate or mitigate at least some of the above presented disadvantages.
SUMMARY OF THE INVENTION

[0007] To cluster multiple database servers in an active-active configuration, one technical challenge is to resolve update conflict. An update conflict refers to two or more database servers updating the same record in the databases that they manage.
Since data in these databases must be consistent among them in order to scale out for performance and achieve high availability, the conflict must be resolved.
Currently TOR_LAW\ 6386957\1 2 there are two different schemes of conflict resolution: (1) time based resolution; and (2) location based resolution. However, neither conflict resolution schemes can be enforced without some heuristic decision to be made by human intervention.
Consequently, most clustered database configurations adopt the active-standby model, and fail to achieve high performance and availability at the same time.
Further, it is recognized that collisions between two or more concurrent transactions in a selected database needs to be addressed. Contrary to current database configurations there is provided a system and method for duplicating a plurality of transactions for a primary database received from at least one application over a network as a plurality of replicated transactions for a secondary database. The system comprises a status module for monitoring a completion status of each of the plurality of transactions received by the primary database, such that the completion status indicates a respective transaction of the plurality of transactions has been successfully processed by the primary database. The system comprises a global queue for storing each of the plurality of transactions for facilitating the transaction duplication in a selected transaction sequence order, wherein the global queue is configured for storing the plurality of transactions and the respective completion status of each of the plurality of transactions including a respective transaction identification. The respective transaction identification represents a unique sequence identification for each stored transaction of the plurality of transactions. The system comprises a controller module coupled to the global queue and configured for assigning the respective transaction identification to each of the plurality of transactions and further configured for duplicating as the plurality of replicated transactions all of the transactions with a successful completion status of the plurality of transactions for storage in a replication queue for facilitating transmission of the plurality of replicated transactions to the secondary database for processing.

[0008] One aspect provided is a system for duplicating a plurality of transactions for a primary database received from at least one application over a network as a plurality of replicated transactions for a secondary database, the system comprising: a status module for monitoring a completion status of each of the plurality of transactions received by the primary database, the completion status for indicating a respective transaction of the plurality of transactions has been successfully processed by the primary database; a global queue for storing each of the TOR_LAW\ 6386957\1 3

9 plurality of transactions for facilitating the transaction duplication in a selected transaction sequence order, the global queue configured for storing the plurality of transactions and the respective completion status of each of the plurality of transactions including a respective transaction identification, the respective transaction identification representing a unique sequence identification for each stored transaction of the plurality of transactions; and a controller module coupled to the global queue and configured for assigning the respective transaction identification to each of the plurality of transactions and further configured for duplicating as the plurality of replicated transactions all of the transactions with a successful completion status of the plurality of transactions for storage in a replication queue for facilitating transmission of the plurality of replicated transactions to the secondary database for processing.
[0009] A further aspect provided is a method for duplicating a plurality of transactions for a primary database received from at least one application over a network as a plurality of replicated transactions for a secondary database, the method comprising the steps of: monitoring a completion status of each of the plurality of transactions received by the primary database, the completion status for indicating a respective transaction of the plurality of transactions has been successfully processed by the primary database; storing each of the plurality of transactions for facilitating the transaction duplication in a selected transaction sequence order, the step of storing the plurality of transactions including storing the respective completion status of each of the plurality of transactions including a respective transaction identification, the respective transaction identification representing a unique sequence identification for each stored transaction of the plurality of transactions; assigning the respective transaction identification to each of the plurality of transactions; and duplicating as the plurality of replicated transactions all of the transactions with a successful completion status of the plurality of transactions for storage in a replication queue for facilitating transmission of the plurality of replicated transactions to the secondary database for processing.
TOR_LAW\ 6386957\1 4 BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Exemplary embodiments of the invention will now be described in conjunction with the following drawings, by way of example only, in which:

[0011] Figure 1A is a block diagram of a system for sequencing transactions;

[0012] Figure 1B is a block diagram of a transaction replicator of the system of Figure 1A;

[0013] Figure 1C, 1D and 1E show an example operation of receiving and processing transactions for the system of Figure 1A;

[0014] Figure 1F shows a further embodiment of the transaction replicator of the system of Figure 1A;

[0015] Figure 2 is a block diagram of a director of the system of Figure 1A;

[0016] Figure 3 is a block diagram of a monitor of the system of Figure 1A;

[0017] Figure 4 is an example operation of the transaction replicator of Figure 1B;

[0018] Figure 5 is an example operation of a global transaction queue and a replication queue of Figure 1B;

[0019] Figure 6 is an example operation of the transaction replicator of Figure 1B for resolving gating and indoubt transactions;

[0020] Figure 7 is an example operation of a replication server of Figure 1B;

[0021] Figure 8 is a further example of the operation of the transaction replicator of Figure 1B; and

[0022] Figures 9a,9b,9c shown a block diagram of a further embodiment of the example operation of Figure 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] A method and apparatus for sequencing transactions in a database cluster is described for use with computer programs or software applications whose functions are designed primarily to replicate update transactions to one or more databases such that data in these databases are approximately synchronized for read and write access.
TOR LAW\ 6386957\1 5

[0024] Referring to Figure 1A, shown is a system 10 comprising a plurality of application servers 7 for interacting with one or more database servers 4 and one or more databases 5 via a transaction replicator 1. It is understood that in two-tier applications, each of the application 7 instances represents a client computer. For three-tiered applications, each of the application 7 instances represents an application server that is coupled to one or more users (not shown). Accordingly, it is recognized that the transaction replicator 1 can receive transactions from applications 7, application servers 7, or a combination thereof. The system 10 allows concurrent updates to be executed on the primary database 5, which then the transactions representing the updates are replicated to the other databases 5 through the transaction replicator, as further described below. Concurrent updates can be viewed as those transactions being processed in parallel in one of the databases 5, where a potential overlap in record access can occur.

[0025] Referring to Figures 1 A and 1B, the transaction replicator 1 of the system 10, receives transaction requests from the application servers 7 and provides sequenced and replicated transactions using a controller 2 to one or more replication servers 3, which apply the transactions to the databases 5. By providing sequencing of transactions in two or more tiered application architectures, the transaction replicator 1 helps to prevent the transaction requests from interfering with each other and facilitates the integrity of the databases 5. For example, a transaction refers to a single logical operation from a user application 7 and typically includes requests to read, insert, update and delete records within a predetermined database 5.

[0026] Referring again to Figure 1A, the controller 2 can be the central command center of the transaction replicator 1 that can run for example on the application servers 7, the database servers 4 or dedicated hardware. The controller 2 may be coupled to a backup controller 9 that is set up to take over the command when the primary controller 2 fails. The backup controller 9 is approximately synchronized with the primary controller such that transaction integrity is preserved. It is recognized that the controller 2 and associated transaction replicator 1 can also be configured for use as a node in a peer-to-peer network, as further described below.

[0027] Referring again to Figure 1A, when a backup and a primary controller are utilized, a replica global transaction queue is utilized. The backup controller 9 TOR LAW\ 6386957\1 6 takes over control of transaction replicator 1 upon the failure of the primary controller 2. Preferably, the primary and backup controllers are installed at different sites and a redundant WAN is recommended between the two sites.

[0028] As is shown in Figure 1B, the controller 2 receives input transactions 11 from a user application 7 and provides sequenced transactions 19 via the replication servers 3, the sequenced transactions 19 are then ready for commitment to the database servers 4. The controller 2 comprises a resent transaction queue (resent TX queue), an indoubt transaction queue 17 (indoubt TX queue), a global transaction sequencer 12 (global TX sequencer), a global TX queue 13 (global TX
queue) and at least one global disk queue 14. The global queue 13 (and other queues if desired) can be configured as searchable a first-in-first out pipe (FIFO) or as a first-in-any-out (FIAO), as desired. For example, a FIFO queue 13 could be used when the contents of the replication queues 15 are intended for databases 5, and a FIAO
queue 13 could be used when the contents of the replication queues 15 are intended for consumption by unstructured data processing environments (not shown). Further, it is recognized that the global disk queue 14 can be configured for an indexed and randomly accessible data set.

[0029] The transaction replicator 1 maintains the globally sequenced transactions in two different types of queues: the global TX queue 13 and one or more replication queues 15 equal to that of the database server 4 instances. These queues are created using computer memory with spill over area on disks such as the global disk queue 14 and one or more replication disk queues 16. The disk queues serve a number of purposes including: persist transactions to avoid transaction loss during failure of a component in the cluster; act as a very large transaction storage (from gigabytes to terabytes) that computer memory cannot reasonably provide (typically less than 64 gigabytes). Further, the indoubt TX queue 17 is only used when indoubt transactions are detected after a certain system failures. Transactions found in this queue have an unknown transaction state and require either human intervention or pre-programmed resolution methods to resolve.

[0030] For example, in the event of a temporary communication failure resulting in lost response from the global TX sequencer 12 to a transaction ID
request, the application resends the request which is then placed in the resent TX
queue 18.
TOR_LAW\ 6386957\1 7 Under this circumstance, there can be two or more transactions with different Transaction ID in the global TX queue 13 and duplicated transactions are removed subsequently.

[0031] In normal operation, the controller 2 uses the global TX queue 13 to track the status of each of the input transactions and to send the committed transaction for replication in sequence. For example, it is recognized that monitoring of the status of the transactions can be done by the director 8, the controller 2, or a combination thereof, when in communication with the database server 4 of the primary database 5, during initial record updating (of the records of the primary database 5) prior to replication (to the secondary databases 5) through use of the global queue 13.

[0032] Referring to Figures 1C, 1D, and 1E, shown is an example operation of the system 10 for receiving and processing a new transaction. In one embodiment, the new transaction is placed in the global queue 13 in preparation for commit time, e.g.
when the transaction ID (represented by references K, L) is issued to the new transaction, thus denoting to the director 8 (or other primary database 5 status monitoring entity) that the new transaction transmit request is recordable to signify that the application 7 is allowed to commit its transmit request (associated with the new transaction) to the database 5.

[0033] In one embodiment, commit time can be defined to include the steps of: 1) the transmit request (associated with the application 7 and the new transaction) is recorded at the director 8; 2) thus providing for passing of the new transaction (e.g.
one or more SQL statements) to the controller 2 by the director 8; 3) the controller 2 then issues the transaction ID (e.g. a commit token K, L) coupled to the new transaction; 4) the new transaction along with the issued transaction ID (e.g.
K, L) are added to the transaction sequence held in the global queue 13; 5) the director passes the transaction commit request (now identified by the transaction ID) to the primary database 5 through the associated database server 4; the director 8 is then in communication with the database server 4 of the primary database 5 in order to determine when the new transaction has been committed successfully in the primary database 5 (e.g. record updates have been persisted to the database 5 ); the director 8 then informs the controller 2 that the new transaction is ready for replication using the transaction ID to identify the new transaction processed by the primary database 5;
TOR_LAW\ 6386957\1 8 and the controller 2 then replicates the new transaction identified by the transaction ID into the replication queues 15.

[0034] In a second embodiment, commit time can be defined to include the steps of: 1) the transmit request (associated with the application 7 and the new transaction) is recorded at the director 8; 2) the director 8 passes the transaction commit request (identification of which is kept track of or otherwise logged by the director 8) to the primary database 5 through the associated database server 4; the director 8 is then in communication with the database server 4 of the primary database in order to determine when the new transaction has been committed successfully in the primary database 5 (e.g. record updates have been persisted to the database 5); the director 8 then informs the controller 2 that the new transaction is ready for replication and passes the new transaction (e.g. one or more SQL statements) to the controller 2; 3) the controller 2 then issues the transaction ID (e.g. a commit token K, L) coupled to the new transaction; 4) the new transaction along with the issued transaction ID (e.g. K, L) are added to the transaction sequence held in the global queue 13; 5) and the controller 2 then replicates the new transaction identified by the transaction ID into the replication queues 15.

[0035] The commit process can be referred to as the fmal step in the successful completion of a previously started database 5 record change as part of handling the new transaction by the replication system 10. Accordingly, the commit process signifies that the process of application (e.g. insertion) of information contained in the new transaction, into all databases' 5 records (both primary and secondary) of the system 10, will be carried out (i.e. replicated), further described below.

[0036] For example, upon receiving the new transaction at commit time, the sequencer 12 assigns a new transaction ID to the received transaction. The transaction ID is a globally unique sequence number for each transaction within a replication group. In Figure 1C, the sequence ID for the newly received transaction is "K". Once the controller 2 receives the transaction, the transaction and its ID are transferred to the global TX queue 20 if there is space available. Otherwise, if the global TX queue 13 is above a predetermined threshold and is full, for example, as TOR_LAW\ 6386957\1 9 shown in Figure 1C, the transaction K and its ID are stored in the global disk queue 14 (Figure 1D).

[0037] Before accepting any new transactions in the global TX queue, the sequencer distributes the committed transactions from the global TX queue 13 to a first replication server 20 and a second (or more) replication server 23 for execution against the databases. As will be discussed, the transfer of the transactions to the replication servers can be triggered when at least one of the following two criteria occurs: 1) a predetermined transfer time interval and 2) a predetermined threshold for the total number of transactions within the global TX queue 13 is met.
However, each replication server 20, 23 has a respective replication queue 21, 24 and applies the sequenced transactions, obtained from the global queue 13, at its own rate.

[0038] For example, when a slower database server is unable to process the transactions at the rate the transactions are distributed by the controller 2, the transactions in the corresponding replication queue are spilled over to the replication disk queues. As shown in Figures 1C and 1D, transaction F is transferred from the global TX queue 13 to the first and second replication servers 20, 23. In the meantime, transactions J and Z are yet to be applied to their respective database servers 4. The first replication server 20 has a first replication queue 21 and a first replication disk queue 22 and the second replication server 23 has a second replication queue 22 and a second replication disk queue 25. The replication queues are an ordered repository of update transactions stored in computer memory for executing transactions on a predetermined database. As shown in Figure 1C, since the second replication queue 24 is above a predetermined threshold (full, for example) transaction F is transferred to the second replication disk queue 25 (Figure 1D).
Similarly in Figure 1E, transaction E is transferred directly from the global TX queue 13 to the first replication disk queue 22. Referring to Figure 1D and Figure 1E, once space opens up in the second replication queue 24 as transaction J and transaction Z
are applied to the corresponding database server 4, the unprocessed transaction F in the second replication disk queue 25 is moved to the second replication queue 24 and transaction E is further accepted into the second replication queue 24 from the global queue. These transactions within the replication queue are ready for subsequent execution of the transaction request against the data within the respective database. In TOR_LAW\ 6386957\1 10 the case where both the replication disk queue and the replication queues are above a preselected threshold (for example, full), an alert is sent by the sequencer 12 and the database is marked unusable until the queues become empty.

[0039] Referring to Figure 1F, shown is the replication server 20 further configured for transmission of the transaction contents 300 of the replication queue 21 (and replication disk queue 22 when used) to two or more database servers 4 that are coupled to respective databases 5. Accordingly, the replicated transactions queued in the replication queue 21 may also be executed concurrently (i.e. in parallel) through multiple concurrent database connections 304 to the second or additional databases 5, for facilitating performance increases in throughput of the replicated transactions 300 against the secondary and/or tertiary databases 5. It is recognised that the replication server 20 coordinates the emptying of the replication queue 21 and disk queue 22 using sequential and/or parallel transmission of the replicated transactions 300 contained therein. The working principle is that when selected ones of the replicated transactions 300 are updating mutually exclusive records Ri, the selected replicated transactions 300 have no sequential dependency and can be executed concurrently using the multiple concurrent database connections 304.
The system allows concurrent execution of transactions on the primary database, as described above. So naturally these transactions executed concurrently on the primary database can be assured exclusivity by the respective database engine/servers 4 through locking, and can be executed concurrently as the replicated transactions 300 on the secondary databases 5 accordingly.

[0040] Further, it is recognised that each of the replicated transactions 300 include one or more individual statements 302(e.g. SQL statement or database record access requests) for execution against the respective database 5. For example, each of the statements 302 in a respective replicated transaction 300 can be used to access different records Ri (e.g. R1 and R2) for the databases 5. The replication server 20 can be further configured for concurrent transmission of individual statements 302, from the same or different ones of the replicated transactions 300, for execution against the same or different databases 5 using the one or more concurrent database connections 304. For example, the SQL statements 302 in one of the replicated transactions 300 may be executed concurrently with the SQL statements 302 from TOR_LAW\ 6386957\1 11 another of the replicated transactions 300 in the replication queue 21. The replication server 20 has knowledge of the contents (one or more individual statements 302)of the replicated transactions 300 to assist in selection (e.g. accounting for execution order and/or which record Ri affected) of which transactions 300 to apply in parallel using the multiple concurrent database connections 304, i.e. have no sequential dependency. This knowledge can be represented in the transaction IDs associated with the replicated transactions 300 and/or the individual statements 302, for example.

[0041] In view of the above, it is also recognised that the replication server 20 can coordinate the transmission of the replicated transactions 300 and/or the individual statements 302 from multiple replication queues 21 to two or more databases 5, as desired.

[0042] The core functions of the controller 2 can be summarized as registering one or more directors 8 and associating them with their respective replication groups;
controlling the replication servers 3 activities; maintaining the global TX
queue 13 that holds all the update transactions sent from the directors 8;
synchronizing the global TX queue 13 with the backup controller 9 (where applicable); managing all replication groups defined; distributing committed transactions to the replication servers 3; tracking the operational status of each database server 4 within a replication group; providing system status to a monitor 6 (and/or the director 8); and recovering from various system failures.

[0043] The registry function of the controller 2 occurs when applications are enabled on a new application server 7 to access databases 5 in a replication group.
Here, the director 8 on the new application server contacts the controller 2 and registers itself to the replication group. Advantageously, this provides dynamic provisioning of application servers 7 to scale up system capacity on demand.
The registration is performed on the first database call (e.g. the transmit request) made by an application. Subsequently the director 8 communicates with the controller 2 for transaction and server 3,4 status tracking.

[0044] The replication server control function allows the controller 2 to start the replication servers 3 and monitors their state. For example, when an administrator requests to pause replication to a specific database 5, the controller 2 then instructs the TOR_LAW\ 6386957\1 12 replication server to stop applying transactions until an administrator or an automated process requests it.

[0045] The replication group management function allows the controller 2 to manage one or more groups of databases 5 that require transaction synchronization and data consistency among them. The number of replication groups that can be managed and controlled by the controller 2 is dependent upon the processing power of the computer that the controller 2 is operating on and the sum of the transaction rates of all the replication groups.
Director

[0046] Referring to Figure 2, shown is a block diagram of the director 8 of the system 10 of Figure 1A. The director can be installed on the application server 7 or the client computer, for example. The director 8 is for initiating a sequence of operations to track the progress of a transaction. The director 8 comprises a first 27, a second 28, a third 29 and a fourth 30 functional module. According to an embodiment of the system 10, the director 8 wraps around a vendor supplied JDBC
driver. As discussed earlier, the director 8 is typically installed on the application server 7 in a 3-tier architecture, and on the client computer in a 2-tier architecture. As a wrapper, the director 8 can act like an ordinary JDBC driver to the applications 7, for example. Further, the system 10 can also support any of the following associated with the transaction requests, such as but not limited to:
1. a database access driver/protocol based on SQL for a relational database 5 (ODBC, OLE/DB, ADO.NET, RDBMS native clients, etc...);
2. messages sent over message queues of the network;
3. XML (and other structured definition languages) based transactions; and 4. other data access drivers as desired.

[0047] As an example, the first module 27 captures all JDBC calls 26 to recognize the new transactions, determines transaction type and boundary, and analyzes any SQLs in the new transaction. Once determined to be an update transaction, the director 8 initiates a sequence of operations to track the progress of the transaction until it ends with a commit or rollback. Both DDL and DML are TOR_LAW\ 6386957\1 13 captured for replication to other databases in the same replication group. The first module 27 can also implement the recording of the transmit requests at commit time.

[0048] The second module 28 collects a plurality of different statistical elements on transactions and SQL statements for analyzing application execution and performance characteristics. The statistics can be exported as comma delimited text file for importing into a spreadsheet.

[0049] In addition to intercepting and analyzing transactions and SQL
statements, the director's third module 29, manages database connections for the applications 7. In the event that one of the databases 5 should fail, the director 8 reroutes transactions (through the fourth module 4) to one or more of the remaining databases 5. Whenever feasible, the director 8 also attempts to re-execute the transactions to minimize in flight transaction loss. Accordingly, the director 8 has the ability to instruct the controller 2 as to which database 5 is the primary database 5 for satisfying the request of the respective application 7.

[0050] Depending on a database's workload and the relative power settings of the database servers 4 in a replication group, the director 8 routes read transactions to the least busy database server 4 for processing. This also applies when a database server 4 failure has resulted in transaction redirection.

[0051] Similarly, if the replication of transactions to a database server 4 becomes too slow for any reason such that the transactions start to build up and spill over to the replication disk queue 16, the director 8 redirects all the read transactions to the least busy database server 4. Once the disk queue becomes empty, the director 8 subsequently allows read access to that database. Accordingly, the fill/usage status of the replication disk queues in the replication group can be obtained or otherwise received by the director 8 for use in management of through-put rate of transactions applied to the respective databases 5.

[0052] For example, when the director 8 or replication servers 3 fails to communicate with the database servers 4, they report the failure to the controller 2 which then may redistribute transactions or take other appropriate actions to allow continuous operation of the transaction replicator 1. When one of the database servers 4 cannot be accessed, the controller 2 instructs the replication server 3 to stop TOR_LAW\ 6386957\1 14 applying transactions to it and relays the database lock down status to a monitor 6.
The transactions start to accumulate within the queues until the database server 3 is repaired and the administrator or an automated process instructs to resume replication via the monitor 6. The monitor 6 may also provide other predetermined administrative commands (for example: create database alias, update parameters, changing workload balancing setting).
Monitor

[0053] Referring again to Figure 1A, the monitor 6 allows a user to view and monitor the status of the controllers 2, the replication servers 3, and the databases 5.
Preferably, the monitor 6 is a web application that is installed on an application or application server 7 and on the same network as the controllers 2.

[0054] Referring to Figure 3, shown is a diagrammatic view of the system monitor 6 for use with the transaction replicator 1. The system monitor 6 receives input data 32 from both primary and backup controllers 2, 9 (where applicable), replication servers 3, the database servers 4 and relevant databases 5 within a replication group. This information is used to display an overall system status on a display screen 31.

[0055] For example, depending on whether the controller is functioning or a failure has occurred, the relevant status of the controller 2 is shown.
Second, the status of each of the replication servers 3 within a desired replication group is shown.
A detailed description of the transaction rate, the number of transactions within each replication queue 15, the number transactions within each replication disk queue 16 is further shown. The monitor 6 further receives data regarding the databases 5 and displays the status of each database 5 and the number of committed transactions.

[0056] The administrator can analyze the above information and choose to manually reroute the transactions. For example, when it is seen that there exists many transactions within the replication disk queue 16 of a particular replication server 3 or that the transaction rate of a replication server 3 is slow, the administrator may send output data in the form of a request 33 to distribute the transactions for a specified amount of time to a different database server within the replication group.
TOR LAW\ 6386957\1 15

[0057] Referring to Figure 4, shown is a flow diagram overview of the method 100 for initializing and processing transactions according to the invention.
The global TX sequencer 12 also referred to as the sequencer hereafter and as shown in Figure 1B, is the control logic of the transaction replicator 1.

[0058] When the controller 2 is started, it initializes itself by reading from configuration and property files the parameters to be used in the current session 101.
The global TX Queue 13, indoubt TX queue 17 and resent TX queue 18 shown in Figure 1B, are created and emptied in preparation for use. Before accepting any new transactions, the sequencer 12 examines the global disk queue 14 to determine if any transactions are left behind from previous session. For example, if a transaction is found on the global disk queue 14, it implies at least one database in the cluster is out of synchronization with the others and the database must be applied with these transactions before it can be accessed by applications. Transactions on the global disk queue 14 are read into the global TX queue 13 in preparation for applying to the database(s) 5. The sequencer 12 then starts additional servers called replication servers 3 that create and manage the replication queues 15. After initialization is complete, the sequencer 12 is ready to accept transactions from the application servers 7.

[0059] The sequencer 12 examines the incoming transaction to determine whether it is a new transaction initiating a commit to its unit of work (e.g.
database record) in the database 5 or a transaction that has already been recorded in the global TX queue 102. For a new transaction, the sequencer 12 assigns a Transaction ID

and records the transaction together with this ID in the global TX queue 13.
If the new transaction ID is generated as a result of lost ID 104, the transaction and the ID are stored in the resent TX queue 109 for use in identifying duplicated transactions. The sequencer 12 checks the usage of the global TX queue 105 to determine if the maximum number of transactions in memory has already been exceeded. The sequencer 12 stores the transaction ID in the global TX queue 13 if the memory is not full 106. Otherwise, the sequencer 12 stores the transaction ID in the global disk queue 107. The sequencer 12 then returns the ID to the application 108 and the sequencer 12 is ready to process another request from the application.
TOR_LAW\ 6386957\1 16

[0060] When a request from the application or application server 7, comes in with a transaction that has already obtained a transaction ID previously and recorded in the global TX queue 13, the sequencer 12 searches and retrieves the entry from either the global TX queue 13 or the disk queue 110. If this transaction has been committed to the database 111, the entry's transaction status is set to "committed" 112 by the sequencer 12, indicating that this transaction is ready for applying to the other databases 200. If the transaction has been rolled back 113, the entry's transaction status is marked "for deletion" 114 and as will be described, subsequent processing 200 deletes the entry from the global TX queue. If the transaction failed with an indoubt status, the entry's transaction status is set to "indoubt" 115. An alert message is sent to indicate that database recovery may be required 116. Database access is suspended immediately 117 until the indoubt transaction is resolved manually 300 or automatically 400.

[0061] Referring to Figure 5, shown is a flow diagram of the method 200 for distributing transactions from the global TX queue 13. The global TX queue 13 is used to maintain the proper sequencing and states of all update transactions at commit time. To apply the committed transactions to the other databases, the replication queue 5 is created by the sequencer 12 for each destination database. The sequencer 12 moves committed transactions from the global TX queue to the replication queue based on the following two criteria: (1) a predetermined transaction queue threshold (Q threshold) and (2) a predetermined sleep time (transfer interval).

[0062] For a system with sustained workload, the Q Threshold is the sole determining criteria to move committed transactions to the replication queue 201. For a system with sporadic activities, both the Q Threshold and transfer interval are used to make the transfer decision 201, 213. Transactions are transferred in batches to reduce communication overhead. When one or both criteria are met, the sequencer 12 prepares a batch of transactions to be moved from the global TX queue 13 to the replication queue 202. If the batch contains transactions, the sequencer 12 removes all the rolled back transactions from it because they are not to be applied to the other databases 204. The remaining transactions in the batch are sent to the replication queue for processing 205. If the batch does not contain any transaction 203, the sequencer 12 searches the global TX queue for any unprocessed transactions (status is TOR LAW\ 6386957\1 17 committing) 206. Since transactions are executed in a same order of occurrence, unprocessed transactions typically occur when a previous transaction has not completed, therefore delaying the processing of subsequent transactions. A
transaction that is being committed and has not yet returned its completion status is called a gating transaction. A transaction that is being committed and returns a status of unknown is called indoubt transaction. Both types of transactions will remain in the state of "committing" and block processing of subsequent committed transactions, resulting in the transaction batch being empty. The difference between a gating transaction and an indoubt transaction is that gating transaction is transient, meaning that it will eventually become committed, unless there is a system failure that causes it to remain in the "gating state" indefinitely. Therefore when the sequencer 12 fmds unprocessed transactions 207 it must differentiate the two types of "committing"
transactions 208. For a gating transaction, the sequencer 12 sends out an alert 209 and enters the transaction recovery process 300. Otherwise, the sequencer 12 determines if the transaction is resent from the application 210, 211, and removes the resent transaction from the global TX queue 211. A resent transaction is a duplicated transaction in the global TX queue 13 and has not been moved to the replication queue 15. The sequencer 12 then enters into a sleep because there is no transaction to be processed at the time 214. The sleep process is executed in its own thread such that it does not stop 200 from being executed at any time. It is a second entry point into the global queue size check at 201. When the sleep time is up, the sequencer 12 creates the transaction batch 202 for transfer to the replication queue 203, 204, 205.

[0063] In a further embodiment, referring to Figures 1 and 8, an example operation 600 of the commit sequence for collision inhibition in replication of the concurrent transactions A,B,C (in a primary database 5a) is shown. Once the transactions A,B,C are received 601 by the director 8, the transactions A,B,C
are passed 602 to the primary database 5a. At this stage, the director 8 can optionally send 605 the transactions A,B,C to the controller 2 to initially get transaction IDs issued and the transactions A,B,C with the IDs are then placed in to the global queue 13 in preparation for replication (i.e. first stage of the replication process). The director 8 then communicates 603 with the database server 4 of the primary database 5a to determine when the statements of each transaction have been processed by the database 5a. For example, shown are the concurrent transactions A,B,C, where TOR_LAW\ 6386957\1 18 transaction A updates 608 record R1, transaction B updates 608 record R5, and transaction C updates 608 records R1 to R5. In this case, as record processing is done by the database 5a, transactions A and B complete first (transaction C is held back from completing due to potential conflicts with records R1 and R5), as indicated by the communication 603 of the transactions' A,B completed status to the director 8.

[0064] Accordingly, the director 8 then requests 604 (i.e. second stage of the replication process or only first stage if step 605 was not followed) to the controller 2 that transactions A,B are ready for commit and are therefore ready for replication. At this stage, the transaction IDs for received transactions A,B are issued by the controller 2 (if not already done so at step 605) and the transactions A,B
with their corresponding IDs are replicated 606 to the replication queues 15. It should be noted that transaction C, if present in the global queue 13, would remain behind in the global queue 13 until the director 8 is informed 607 of completion of transaction C by the database server 4, thus signifying that the director 8 should request subsequent replication (not shown) of the transaction C by the controller 2. The replicated transactions A,B in the queues 15 are then sent 609 to the database servers 4 associated with the secondary/replication databases 5b and processed accordingly.
The director 8 can also get feedback (not shown) from the database servers 4 of the secondary/replication databases 5b to indicate that the transactions A,B have been processed properly.

[0065] Accordingly, the completion status of the transactions A,B,C are monitored by the director 8, or other monitoring entity ¨ e.g. controller 2, such that the transactions A,B,C are each passed 604,605 to the controller 2 at their own determined commit time, or request for commit, thus helping to prevent collisions and therefore to help provide for database 5a,b integrity. For example, the director 8 will not receive a commit request for transaction C until the director 8 acquired transaction IDs for transaction A and B from the controller 2, and sent the commit requests to database server 4 of the primary database 5. The commit requests from transaction A
and B effectively removed the collision condition on records R1 ,R5 for transaction C, allowing transaction C to update R1, R5 and to proceed with a commit request to director 8.
TOR LAW\ 6386957\1 19

[0066] Referring to Figures 9a, 9b, 9c, representing consecutive time intervals ti, t2, t3 respectively, concurrent update transactions T1,T2,T3 (or any number of transactions or transaction types) are forwarded (e.g. by the director 8) to the primary database 5a. It is recognized that during concurrent updating any of the database records R1-R12 (generically identified as Ri) only one of the transactions T1,T2,T3 can access a particular database record Ri at any one time. This restricted access of database records Ri can be implemented though locking of the records Ri currently being processed at any one time by the respective transaction T1,T2,T3 . For example, it is noted in Figure 9a that currently locked records Ri are represented as shaded boxes ¨ e.g. transaction T3 has locked records R9, R10, and R12 at time ti, while transaction T2 has locked records R5,R7,R11 and transaction Ti has locked records R1,R2,R3,R4,R6,R8. It is further noted that transaction Ti is waiting to complete it's record Ri updates to records R9,R10, while transaction T2 is waiting to complete it's record Ri updates to records R8,R9,R10, all waiting records Ri represented as crosshatched boxes in Figure 9a. Accordingly, each of the concurrent transactions T1,T2,T3 are able to lock exclusively some records Ri to access/update as well as to wait on those other records Ri that other concurrent transactions T1,T2,T3 are in the process of updating (or otherwise accessing). At any given point in time tl,t2,t3, a different combination of update transactions T1,T2,T3,T4,T5 can be executing simultaneously.

[0067] Referring to Figure 9a, at time ti, for example, three concurrent update transactions T1,T2,T3 are executing, where transaction T3 successfully updated all the required records R9,R10,R12, while transactions Ti and T2 are waiting for transaction T3 to commit the changes to the records R9, R10 and R12.
Therefore, transaction T3 is the only transaction that at time ti can possibly request a Transaction ID (Commit Token) from the replication system 10 (e.g. where the director 8 passes the transaction T3 to the controller 2 for subsequent issuance of the corresponding transaction ID and placement in the global queue 13 for subsequent replication to the replication queues 15), despite the fact that transaction T3 is started after transactions Ti and T2. With the transaction ID granted, transaction T3 proceeds to commit its unit of work in the primary database 5a, thus providing for replication of the transaction T3 via the controller 2 to the secondary databases 5b (see Figure 8), as described above by example. It is recognized that the concurrent transactions TOR_LAW\ 6386957\1 20 T1,T2,T3 may also be ordered by the director 8 and/or the database server 4 of the primary database 5a due to time stamping or other means of transaction sequencing.

[0068] Referring to Figure 9b, at time t2 following time ti, transaction Ti successfully locked the records R9 and R10 and updated them, after transaction released the respective locks, while transaction T2 waits for transaction Ti to release the records R8, R9 and R10. At the same time a new update transaction T4 is received by the database server 4 (see Figure 9b) starts to execute in the primary database 5a. It is noted at time t2, transaction Ti is the only transaction that can request its Transaction ID from replication system 10 (as described above by example) to complete its unit of work in the primary database 5a, thus providing for replication of the transaction Ti via the controller 2 to the secondary databases 5b (see Figure 8). It is further noted at time t2 that transaction T4 is waiting on records R2,R4,R6 locked by transaction Ti and R7 locked by transaction T2.

[0069] Referring to Figure 9c, at time t3 following time t2, transaction T5 started execution in the primary database 5a and successfully updated records R1 and R3, while transaction T2 also successfully updated records R8, R9 and R10.
Both transactions T2,T5 request respective transaction IDs from the replication system 10, as described above by example, to complete their unit of work, while transaction T4 continues to wait for transaction T2 and T5 to complete their units of work in the primary database 5a, thus providing for replication of the transactions T2,T5 via the controller 2 to the secondary databases 5b (see Figure 8).

[0070] In view of Figures 9a,9b,9c, it is recognized that the database server 4 (see Figure 8) of the primary database 5a can indicate to the director 8 that the transactions T3 ,T2,T5 were completed and thus were candidates for being issued their respective transaction IDs in preparation for replication of the transactions T3 ,T2,T5 to the secondary databases 5b.

[0071] Referring to Appendix A, an example embodiment of the replication transaction sequencing is provided, where Ti represents the instance of time in the database 5 engine, Ui represents an update statement of the transaction for processing and eventual replication, Di represents a delete statement of the transaction for processing and eventual replication, Si represents a select statement of the transaction =
TOR_LAW\ 6386957\1 21 for processing and eventual replication, Ri represents records currently locked (lock list) for the transaction, Wi represents records Ri to be locked (lock wait list), W
represents wait action for lock, C represents eligible to commit action for the completed transaction to the replication queues 15, R represents victimized action to rollback for the transaction, a Lock Dependency set when evaluated to empty set F
implies logical "True" or (C "Eligible to commit"), the Lock Dependency set when evaluated to non-empty set F' implies logical "False" or (W "Wait for lock"), and Sequence represents the replication sequence of the transactions to the other databases 5b. It is recognized that the sequencing information can be accessible or otherwise hosted by the database server 4 (e.g. of the primary database 5a), the director 8, the controller 2, other system entities not shown, or a combination thereof.

[0072] Further, it is recognized that the replication system 10 can be implemented inside a database engine (RDBMS), not shown, as an alternative embodiment. For example, the database engine (e.g. of IBM's DB2 product) can incorporate the replication system 10, including such as but not limited to including the functionality (or a portion thereof) of the director 8 and/or the controller 2 and/or hosting of the global queue 13 and/or the respective replication queue 15.

[0073] Referring to Figure 6, shown is a flow diagram illustrating the method 300 for providing manual recovery of transactions 116 as shown in Figure 100.
There are two scenarios under which the sequencer 12 is unable to resolve gating transactions and indoubt transactions caused by certain types of failure and manual recovery may be needed. First, a gating transaction remains in the global TX
queue 13 for an extended period of time, stopping all subsequent committed transactions from being applied to the other databases. Second, a transaction status is unknown after some system component failure. The sequencer 12 first identifies the transactions causing need resolution 301 and send out an alert 302. Then the transaction can be manually analyzed to determine whether the transaction has been committed or rolled back in the database 304 and whether any manual action needs to be taken. If the transaction is found to have been rolled back in the database, the transaction entry is deleted manually from the global TX queue 305. If the transaction has been committed to the database, it is manually marked "committed" 306. In both cases the replication process can resume without having to recover the database 500.
TOR_LAW\ 6386957 \ 1 22 If the transaction is flagged as indoubt in the database, it must be forced to commit or roll back at the database before performing 304, 305 and 306.

[0074] Referring again to Figure 6, the process 400 is entered when an indoubt transaction is detected 115 and automatic failover and recovery of a failed database is performed. Unlike gating transactions that may get resolved in the next moment, an indoubt transaction is permanent until the transaction is rolled back or committed by hand or by some heuristic rules supported by the database. If the resolution is done with heuristic rules, the indoubt transaction will have been resolved as "committed" or "rolled back" and will not require database failover or recovery.
Consequently the process 400 is only entered when an indoubt transaction cannot be heuristically resolved and an immediate database failover is desirable. Under the automatic recovery process, the database is marked as "needing recovery" 401, with an alert sent out 402 by the sequencer 12. To help prevent further transaction loss, the sequencer 12 stops the generation of new transaction ID 403 and moves the indoubt transactions to the indoubt TX queue 404. While the database is marked "needing recovery" the sequencer 12 replaces it with one of the available databases in the group 405 and enables the transaction ID generation 406 such that normal global TX
queue processing can continue 200. The sequencer 12 then executes a user defined recovery procedure to recover the failed database 407. For example, if the database recovery fails, the recovery process is reentered 408, 407.

[0075] Referring to Figure 7, shown is a flow diagram illustrating the processing of committed transactions by the replication servers 3 and the management of transactions in the replication queue 15 according to the present invention.
Replication queues 15 are managed by the replication servers 3 started by the sequencer 12. One of the replication servers 3 receives batches of transactions from the sequencer 12. The process 500 is entered if a new batch of committed transactions arrives or at any time when queued transactions are to be applied to the databases.

[0076] If the process is entered because of new transactions 501, the batch of transactions is stored in the replication queue in memory 508, 509, or in replication disk queue 511 if the memory queue is full. Replication disk queue capacity is determined by the amount of disk space available. If the disk is above a TOR LAW\ 6386957\1 23 predetermined threshold or is full for example 510, an alert is sent 512 by the sequencer 12 and the database is marked unusable 513 because committed transactions cannot be queued up anymore.

[0077] If the process is entered in an attempt to apply transactions in the replication queue to the databases, the replication server first determines whether there is any unprocessed transaction in the replication queue in memory 502.
If the memory queue is empty but unprocessed transactions are found in the replication disk queue 503, they are moved from the disk queue to the memory queue in batches for execution 504, 505. Upon successful execution of all the transactions in the batch they are removed from the replication queue by the replication server and another batch of transactions are processed 501. If there are transactions in the replication disk queue 16, the processing continues until the disk queue is empty, at which time the replication server 3 waits for more transactions from the global TX queue 501.
During execution of the transactions in the replication queue 15, error may occur and the execution must be retried until the maximum number of retries is exceeded 507, then an alert is sent 512 with the database marked unusable 513. However, even though a database is marked unusable, the system continues to serve the application requests.
The marked database is inaccessible until the error condition is resolved. The replication server 3 stops when it is instructed by the sequencer during the apparatus shutdown process 118, 119 and 120 shown in Figure 4.

[0078] It will be evident to those skilled in the art that the system 10 and its corresponding components can take many forms, and that such forms are within the scope of the invention as claimed. For example, the transaction replicators 1 can be configured as a plurality of transaction replicators 1 in a replicator peer-to-peer (P2P) network, in which each database server 4 is assigned or otherwise coupled to at least one principal transaction replicator 1. The distributed nature of the replicator P2P
network can increase robustness in case of failure by replicating data over multiple peers (i.e. transaction replicators 1), and by enabling peers to find/store the data of the transactions without relying on a centralized index server. In the latter case, there may be no single point of failure in the system 10 when using the replicator network. For example, the application or application servers 7 can communicate with a selected one of the database servers 7, such that the replicator P2P network of TOR_LAW\ 6386957\1 24 transaction replicators 1 would communicate with one another for load balancing and/or failure mode purposes. One example would be one application server 7 sending the transaction request to one of the transaction replicators 1, which would then send the transaction request to another of the transaction replicators 1 of the replicator P2P network, which in turn would replicate and then communicate the replicated copies of the transactions to the respective database servers 4.

[0079] Further, it is recognized that the applications/ application servers 7 could be configured in an application P2P network such that two or more application computers could share their resources such as storage hard drives, CD-ROM
drives, and printers. Resources would then accessible from every computer on the application P2P network. Because P2P computers have their own hard drives that are accessible by all computers, each computer can act as both a client and a server in the application P2P networks (e.g. both as an application 7 and as a database 4).

networks are typically used for connecting nodes via largely ad hoc connections. Such P2P networks are useful for many purposes, such as but not limited to sharing content files, containing audio, video, data or anything in digital format is very common, and realtime data, such as Telephony traffic, is also passed using P2P technology.
The term "P2P network" can also mean grid computing. A pure P2P file transfer network does not have the notion of clients or servers, but only equal peer nodes that simultaneously function as both "clients" and "servers" to the other nodes on the network. This model of network arrangement differs from the client-server model where communication is usually to and from a central server or controller. It is recognized that there are three major types of P2P network, by way of example only, namely:
1) Pure P2P in which peers act as clients and server, there is no central server, and there is no central router;
2) Hybrid P2P which has a central server that keeps information on peers and responds to requests for that information, peers are responsible for hosting the information as the central server does not store files and for letting the central server know what files they want to share and for downloading its shareable resources to peers that request it, and route terminals are used as addresses which are referenced by a set of indices to obtain an absolute address; and 3) Mixed P2P which has both pure and hybrid characteristics.
TOR _LAW 6386957\1 25 Accordingly, it is recognized that in the application and replicator P2P
networks the applications/ application servers 7 and the transaction replicators 1 can operate as both clients and servers, depending upon whether they are the originator or receiver of the transaction request respectively. Further, it is recognized that both the application and replicator P2P networks can be used in the system 10 alone or in combination, as desired.
In view of the above, the spirit and scope of the appended claims should not be limited to the examples or the description of the preferred versions contained herein.
TOR_LAW\ 6386957\1 26 Annendix A
Time SQL Record Set Lock Dependency Action Sequence Ui {R, W} {Wx} n {Ry} 0 4:1 v {Wx } n {Rz} # (1) W -Ti U2 {Ry, Wy} { Wy} n IRO = 0 A {Wy} n {Rz} = cr. C

U3 {R, W} {Wz} n {Rx} = 0 A Ma n IRO = (1) C 2 Ui {R, W} {Wx} n (Ry1 0 cp v {Wx} n {11,1 0 cD W -T2 U4 {R, Wy} {Wy} n {Rx} = 0 A {W} n {itz} = 0 C 3 U5 {R, W} (Wz} n (R.) # cp v {Wz1 n {Ry} 0 cr. W -U1 {R, W} {WO n {Ry1 = cre A {Wx} n {Rz} = cD C

T3 U5 {Rz, Wz} {Wz} n {Rx} = ()A {Wz} n {Ry} = cre C

U6 {Ry, Wy} {Wy} n {Rx} 0 cD v {Wy} r) {Rz} 0 CD W -, U6 {R, W} {Wy} n {KJ = (13 A {Wy} n {Rz} = (I) C

T4 U7 { Rz, Wx} {Wx} n {Ry} # CD v {Wx } n {V # cD W -U8 {R, W} {Wz} n {Rx} = CD A {Wz} n {Ry} = ID C

U7 {Rz, Wx} {W} n {Ry} = 0 A {W} n {Rz} = cp C 8 T5 19 {R, W} {Wy} = (13 V ({Wy} n {Rx} = 0 A {Wy} n {Rz} = cr.) 110 {R., Wz} {Wz} = CD v ({Wz} n IRO =43 A {Wz} n {Rx} = 0) Sll {Rx, Wx} {Wx} = cD C -T6 U12 {Ry, Wy} {Wy} n {itx} # (Dv {Wy} n {Rz} 0 c13 W -U13 {R, W} {Wz} n {Rx} = (13 A {Wz} n IRO =43 C 11 Sii 1%, Wx} {Wx} = (13 C -T7 U12 {Ry, Wy} {Wy} n {R.} # 0 A {Wy} n {Rz} = 0:13 w -D14 {R, W} {Wz1 n {Rx} 0 .r. v {Wz} n {Ry} (1) W -U12 {R, W} {Wy} n {Rx} # 0 A MO n {Rz} = cr. W -T8 D14 {Rz, Wz} {Wz} n 1RJ= CD A {Wz} n IRO =4) C 12 D15 {Rx, Wx} {Wx} n {Ry} # 0 A {Wx} n {Rz} #.13 R -, U12 {R, W} {Wy} n {Rx} = (1) A {Wy} n {Rz} =c1) C

T9 116 Iltx, W.} {Wx} n {Ry} = cp A IWO n {Rz} = 0:1) C

U17 {R, W} {Wx} n {Rx} # (13 v {Wz} n {Ry} # cD W -T10 U17 {tz, Wz} {Wz} = 4) C 15 TOR_LAW\ 6386957\1 27 ,

Claims

What is Claimed:

1. A system for receiving and tracking a plurality of transactions and distributing the transactions to at least two replication queues over a network, the system comprising:
a first computer system comprising at least one controller, the at least one controller further comprising:
a global queue configured to store a number of the received transactions in a first predetermined order;
a sequencer coupled to the global queue configured to:
prepare a batch of transactions from the number of the received transactions;
distribute, in a second predetermined order that is different from the first predetermined order, said batch of transactions to each of said at least two replication queues; and remove from said batch of transactions a rolled back transaction prior to said batch of transactions being distributed; and an indoubt transaction queue in communication with the sequencer, the indoubt transaction queue configured to store the transactions identified as having unknown status by a database server during a system failure.

2. The system according to claim 1, wherein the sequencer is further configured to distribute said batch of transactions at a predetermined time interval.

3. The system according to claim 1, wherein the sequencer is further configured to distribute said batch of transactions when the number of the transactions within the global queue exceeds a predetermined value.

4. The system according to claim 1, wherein the sequencer is further configured to distribute said batch of transactions upon the earlier of:
a predetermined time interval; and the number of the transactions within the global queue exceeds a predetermined value.

5. The system according to claim 4, wherein each of the transactions comprises an update transaction and a unique transaction id assigned by the sequencer.

6. The system according to claim 5, further comprising a global disk queue in communication with the global queue configured to receive and store the transactions when the global queue is above a global threshold.

7. The system according to claim 6, wherein each of said at least two replication queues have a corresponding replication disk queue configured to receive and store the transactions from the global queue when the corresponding replication queue is above a replication threshold.

8. The system according to claim 7, wherein the global queue is further configured to receive the transactions from the global disk queue when the global disk queue is other than empty, and the global queue is further configured to receive the transactions from at least one application server when the global disk queue is empty.

9. The system according to claim 5, wherein the update transaction comprises at least one of a read, insert, update or delete request for at least one database in communication with at least one of said at least two replication queues.

10. The system according to claim 5, further comprising a resent transaction queue configured to store a transaction that repeats a request for the transaction id.

11. The system according to claim 1, wherein the global queue is further configured to receive the received transactions from a network entity selected from the group comprising: an application, and an application server.

12. The system according to claim 1, wherein the global queue is a searchable first-in first-out pipe.

13. The system according to claim 12, wherein the sequencer is further configured to assure the order of transactions in the global queue remain consistent with their execution order at a database server coupled to at least one of the replication queues.

14. The system according to claim 12, wherein the global queue is further configured to store an indexed and randomly accessible data set.

15. The system according to claim 1, wherein the global queue and sequencer are hosted on a network entity selected from the group comprising: a central control server and a peer-to-peer node.

16. A system for receiving a plurality of transactions from at least one application server comprising a processor, distributing the transactions to at least two replication queues, and applying the transactions to a plurality of databases, the system comprising:
a director coupled to each of said at least one application server configured to capture a plurality of database calls therefrom as the plurality of transactions; and a controller configured to receive each of the plurality of transactions, the controller further configured to:
store the transactions within a global queue in a predetermined order, generate a batch of transactions from the plurality of transactions stored in the global queue for each of said at least two replication queues, remove a rolled back transaction from said batch of transactions, thereafter, transmit in the predetermined order said batch of transactions to each of said at least two replication queues; and store a transaction of the plurality of transactions identified as having unknown status by a database server during a system failure in an indoubt transaction queue.

17. The system according to claim 16, further comprising at least two replication servers comprising said at least two replication queues, wherein each of said at least two replication servers is coupled to each of the databases, and the director is further configured to route each of the transactions to one or more of the databases relative to workload and transaction throughput of the one or more databases.

18. The system according to claim 17, further comprising a backup controller configured to receive the transactions from said at least one application server upon failure of the controller, the backup controller comprising a backup global queue, wherein the backup global queue is synchronized with the controller and the backup global queue is a copy of the global queue.

19. A method for receiving and tracking a plurality of transactions and distributing the transactions to at least two replication queues over a network, the method comprising:
storing a number of the received transactions in a first predetermined order in a global queue;
creating a batch of transactions from the transactions for each of said at least two replication queues;
removing a rolled back transaction from said batch of transactions;
thereafter distributing in a second predetermined order said batch of transactions to each of said at least two replication queues; wherein distributing said batch of transactions comprises assuring the order of transactions in the global queue remain consistent with their execution order at a database server coupled to at least one of the replication queues; and storing a transaction of the plurality of transactions within an indoubt transaction queue during a system failure.

20. The method according to claim 19, wherein the distributing of said batch of transactions occurs at a predetermined time interval.

21. The method according to claim 19, wherein the distributing of said batch of transactions occurs when the number of the transactions within the global queue exceeds a predetermined number.

22. The method according to claim 19, wherein the distributing of said batch of transactions occurs upon the earlier of: a predetermined time interval; and the number of the transactions within the global queue exceeds a predetermined number.

23. The method according to claim 22, further comprising assigning an update transaction and a unique transaction id to each of the transactions.

24. The method according to claim 23, further comprising receiving and storing the transactions within a global disk queue when the global queue storage capacity reaches a global threshold.

25. The method according to claim 24, further comprising:
determining whether the global disk queue is other than empty; and receiving the transaction from the global disk queue rather than receiving the transactions from at least one application server when the global disk queue is other than empty.

26. The method according to claim 23, wherein the update transaction comprises at least one of a read, insert, update or delete request for at least one database in communication with at least one of said at least two replication queues.

27. The method according to claim 22, further comprising:
determining when at least one of said at least two replication queues are above a replication threshold, each of said at least two replication queues having a corresponding replication disk queue;
storing a number of the transactions within said corresponding replication disk queue based upon the determination; and sending an alert to notify when said at least two replication queues and said corresponding replication disk queue capacity reach a preselected threshold.

28. The method according to claim 27, further comprising:
redirecting the transactions to at least one of said at least two replication queues being below said preselected threshold, based on receiving the alert.

29. A system for receiving and tracking a plurality of transactions and distributing the transactions to at least two replication queues over a network, the system comprising:
a first computer system comprising at least one controller, the at least one controller further comprising:
a global queue configured to store a number of the received transactions in a first predetermined order; and a sequencer coupled to the global queue configured to:
prepare a batch of transactions from the number of the received transactions;

distribute, in a second predetermined order that is different from the first predetermined order, said batch of transactions to each of said at least two replication queues when the number of the transactions within the global queue exceeds a predetermined value; and remove from said batch of transactions a rolled back transaction prior to said batch of transactions being distributed.

30. A system for receiving and tracking a plurality of transactions and distributing the transactions to at least two replication queues over a network, the system comprising:
a first computer system comprising at least one controller, the at least one controller further comprising:
a global queue configured to store a number of the received transactions in a first predetermined order; and a sequencer coupled to the global queue configured to:
prepare a batch of transactions from the number of the received transactions;
distribute, in a second predetermined order that is different from the first predetermined order, said batch of transactions to each of said at least two replication queues; and remove from said batch of transactions a rolled back transaction prior to said batch of transactions being distributed;
wherein the sequencer is further configured to distribute said batch of transactions upon the earlier of: a predetermined time interval; and the number of the transactions within the global queue exceeds a predetermined value.

31. A system for receiving a plurality of transactions from at least one application server comprising a processor, distributing the transactions to at least two replication queues, and applying the transactions to a plurality of databases, the system comprising:
a director coupled to each of said at least one application server configured to capture a plurality of database calls therefrom as the plurality of transactions;

a controller configured to receive each of the plurality of transactions, the controller further configured to:
store the transactions within a global queue in a predetermined order, generate a batch of transactions from the plurality of transactions stored in the global queue for each of said at least two replication queues, remove a rolled back transaction from said batch of transactions, and thereafter, transmit in the predetermined order said batch of transactions to each of said at least two replication queues; and a backup controller configured to receive the transactions from said at least one application sever upon failure of the controller, the backup controller comprising a backup global queue, wherein the backup global queue is synchronized with the controller and the backup global queue is a copy of the global queue.

32. A method for receiving and tracking a plurality of transactions and distributing the transactions to at least two replication queues over a network, the method comprising:
storing a number of the received transactions in a first predetermined order in a global queue;
creating a batch of transactions from the transactions for each of said at least two replication queues;
removing a rolled back transaction from said batch of transactions; and thereafter distributing in a second predetermined order said batch of transactions to each of said at least two replication queues when the number of the transactions within the global queue exceeds a predetermined number; wherein distributing said batch of transactions comprises assuring the order of transactions in the global queue remain consistent with their execution order at a database server coupled to at least one of the replication queues.

33. A method for receiving and tracking a plurality of transactions and distributing the transactions to at least two replication queues over a network, the method comprising:
storing a number of the received transactions in a first predetermined order in a global queue;
creating a batch of transactions from the transactions for each of said at least two replication queues;

removing a rolled back transaction from said batch of transactions; and thereafter distributing in a second predetermined order said batch of transactions to each of said at least two replication queues; wherein distributing said batch of transactions comprises assuring the order of transactions in the global queue remain consistent with their execution order at a database server coupled to at least one of the replication queues;
wherein the distributing of said batch of transactions occurs upon the earlier of: a predetermined time interval; and the number of the transactions within the global queue exceeds a predetermined number.

34. A method for receiving and tracking a plurality of transactions and distributing the transactions to at least two replication queues over a network, the method comprising:
storing a number of the received transactions in a first predetermined order in a global queue;
creating a batch of transactions from the transactions for each of said at least two replication queues;
removing a rolled back transaction from said batch of transactions;
thereafter distributing in a second predetermined order said batch of transactions to each of said at least two replication queues; wherein distributing said batch of transactions comprises assuring the order of transactions in the global queue remain consistent with their execution order at a database server coupled to at least one of the replication queues;
storing one or more of the received transactions within a global disk queue when the global queue storage capacity reaches a global threshold; and determining whether the global disk queue is other than empty; and receiving the one or more of the received transactions from the global disk queue rather than receiving the transactions from at least one application server when the global disk queue is other than empty.

35. A method for receiving and tracking a plurality of transactions and distributing the transactions to at least two replication queues over a network, the method comprising:
storing a number of the received transactions in a first predetermined order in a global queue;
creating a batch of transactions from the transactions for each of said at least two replication queues;
removing a rolled back transaction from said batch of transactions;

thereafter distributing in a second predetermined order said batch of transactions to each of said at least two replication queues; wherein distributing said batch of transactions comprises assuring the order of transactions in the global queue remain consistent with their execution order at a database server coupled to at least one of the replication queues;
determining when at least one of said at least two replication queues are above a replication threshold, each of said at least two replication queues having a corresponding replication disk queue;
storing a number of the transactions within said corresponding replication disk queue based upon the determination; and sending an alert to notify when said at least two replication queues and said corresponding replication disk queue capacity reach a preselected threshold.