JPH04155548A - Log management and recovery processing system - Google Patents

Abstract

PURPOSE:To ensure a page operational sequence by a time sequential log data at the time of a recovering processing by writing out a log in a nonvolatile storage device to manage the log, in the sequence of the completion of a transaction, rearranging this log in the sequence of a logical time, and recovering the page of a data base in this sequence. CONSTITUTION:This system is equipped with a log managing part 16 which writes out a log 19 having the logical time in a log storing nonvolatile storage device 18 in order to manage the log, in the sequence of the completion of the transaction, at the time of the completion of the transaction, and a recovery processing part 20 which rearranges the log 19 which is written out in the log storing nonvolatile storage device 18 in the sequence of the logical time, and recovers a page 12' of a data base 10' in this sequence, at the time of the fault of a data base 10. Then, the log which is not managed as the time sequential data is preliminarily noted based on the logical time in the log at the time of the recovering processing. Thus, the page operational sequence by the time sequential log data at the time of the recovering processing can be ensured, without deteriorating the performance at the time of a usual task.

Description

[Detailed Description of the Invention] [Summary] A database management system having an exclusive control function on a record basis, which uses a logical time indicating the chronological order of updates.
This invention relates to a log management/recovery processing method in a system that recovers database pages in the event of a failure based on logical time by having database pages and logs.

The purpose of this invention is to guarantee the order of page operations based on time-series log data during recovery processing without deteriorating performance during normal business operations even when record-based transaction exclusion is used.

A log management means that writes and manages logs to a non-volatile storage device in the order of transaction completion when a transaction is completed, and a log management means that arranges the logs written to the non-volatile storage device in the order of logical time when the database is restored. and a recovery processing means for recovering the pages of the database in the order of the logs that have been changed and sorted.

[Industrial application field]

The present invention is a database management system having an exclusive control function on a record-by-record basis, and has a logical time indicating the chronological order of updates in the database and log, so that it can be used in the event of a failure. This invention relates to log management and recovery processing methods in a system that recovers pages of a database based on logical time.

Generally, database access through online real-time transactions requires responsive performance. Furthermore, when a failure occurs, it is necessary to restore the 5-database to the state before the failure occurred by using log data, etc. [Prior Art] In the event of a database failure, recovery is impossible.

This is done using the pre-update log/post-update log obtained when updating the database. For example, Japanese Patent Application Laid-Open No. 1983-1980
A system such as that shown in Publication No. 220438 (name of invention: two-log control system) is known. In this method, each page of the database has logical time information that independently indicates the update level, and when that page is updated, the information specifying the page and the logical time information are recorded in the log of f. (9) This enables accurate correspondence between the log and page state, and prevents fuzzy dumps.
Even in an environment that allows p), the number of logs required is far less than that of other conventional technologies.

Traditionally, in such database management systems. performs exclusive control at two different levels to prevent data inconsistency due to access conflicts between transactions, but when each page has a logical time,
Exclusive control of transactions was performed on a page-by-page basis.

FIG. 4 shows an example of the prior art.

It is assumed that transaction TRNI updates record A in page P in database 10, and transaction TRN2 updates record B in the same page P.

Transaction TRN1 first acquires exclusive transaction rights for page P. Once exclusive rights are acquired, record A is updated.

At that time, the pages of the database 1o, where the pre-update log/post-update log is collected in a buffer (not shown), are assigned a logical time (for example, the value of the number of updates) tl to indicate the chronological order of updates. Set.

When this transaction TRN 1 commits (com
mit), the log on the buffer is written to the log storage non-volatile storage device 18, which is constituted by a magnetic disk device, a memory with source backup, etc., and the exclusive control over page P is released.

Note that a commit is an update or addition made within a transaction at the end of the transaction because the processing request by the transaction has been completed.

This refers to confirming and validating data such as deletion.

On the other hand, transaction TRN2 issues an exclusive request for page P in order to update record B. At this time, if transaction TRN1 has already acquired the exclusive right, the processing of transaction TRN2 is different from the processing of transaction TRN1. The user is forced to wait until the exclusive right to page P is released.

When transaction TRNI releases exclusive access to page P and transaction TRN2 acquires the exclusive right, it updates record B and collects its log (Log-B). When transaction TRN2 is committed, log (Log-B) 19 is written to log storage nonvolatile storage device 18, and transaction exclusion of page P is released.

When it becomes necessary to restore the database 10 to the state before the failure due to a failure, the log I9 is read and the logical time El indicating the chronological order of updates is read.

According to t2, page P of the database 10 is restored.

When transaction exclusion is performed on a page-by-page basis, the order in which logs 19 are output is in the order of logical time, and when logs are stored in the write-once format, the order of logical time is There is no reversal.

[Problem to be solved by the invention]

If exclusive control between transactions is performed in large units, there is a high possibility that transactions will be waiting for exclusion release, and in the event of a conflict, processing of one transaction will be forced to wait for a long time. Therefore, one-layer exclusive control is performed, although the control becomes more complicated.

The idea is to perform exclusive control in as small a unit as possible. As the smallest unit of exclusive control.

Exclusive control on a record basis can be considered.

FIG. 5 is a diagram illustrating problems with the prior art when transactions are excluded on a record-by-record basis.

■ Transaction TRN 1 acquires exclusive transaction rights for record A in order to update record A, and updates record A in page P. At this time, the logical update time tl is stored in the page P.

■ On the other hand, transaction TRN2 is on the same page P
In order to update record B therein, exclusive transaction rights to record B are acquired and record B is updated. The logical time of update is.

t2 (however, t2>tl in this example).

Even if they are on the same page P, the records that are the unit of exclusion are different, so transactions TRN1 and TRN2 can run at the same time.

■ Transaction TRN2 completes its processing first, and the log (L.

g-B).

(2) Thereafter, transaction TRN1 writes a log (Log-A) at the time of commit.

In the above sequence, the order of updates and the order of writing the log 19 are reversed.

Due to the occurrence of a failure, the recovery processing unit 50
When attempting to restore page P, the restoration process is performed in the order of log 19, so if restoration is performed using log (Log-B), the logical time of page P becomes t2. A), but the logical time t1 is older than the logical time t2 of page P, so the log (
Log-A) is rejected.

In the case of a system that performs recovery processing using logs that have logical times in pages and logs, when page exclusion is assumed, logs generated for a certain page are
As shown in the figure, this is guaranteed as time-series data that corresponds to updates to that page.

However, when record-based exclusion is assumed, as shown in Figure 5, the order in which logs occur for a certain page is not necessarily guaranteed as time-series data corresponding to updates to that page. , Therefore, there is a problem that the page cannot be restored in the recovery process.

On the other hand, when writing logs when a transaction is committed, in order to guarantee the order in which the logs occur, instead of storing the logs in an append format, the logs are inserted in chronological order. There is a problem in that the overhead of the writing process becomes large and the processing efficiency during normal business operations decreases.

The present invention aims to solve the above problems, even when using record-based transaction exclusion.

The purpose is to guarantee the order of page operations using time-series log data during recovery processing without degrading performance during normal business operations.

[Means to solve the problem]

As shown in FIG. 1, in a database management system that performs exclusive control of transactions on a record-by-record basis, when a transaction is completed, a log 19 having a logical time is stored in a non-volatile memory for log storage in the order of completion of the transaction. A log management unit 16 that writes data to a storage device 18 and manages the log.

When a failure occurs in the database 10, the logs 19 written in the log storage nonvolatile storage device 21B are rearranged in logical time order, and pages 12 of the database 10' are stored in the rearranged order of the logs 19. '.

[Effect]

The present invention (i) serializes updates of in-page management information including logical times indicating the chronological order of updates; (ii) Logs that are not managed as 2-time series data are sorted in advance based on the logical time within the logs during recovery processing. According to this, the same recovery process as in page-based exclusion can be used without increasing the overhead at the end of a transaction.

〔Example〕

FIG. 1 shows an example of the configuration of the present invention, FIG. 2 shows an example of log collection and storage according to an embodiment of the invention, and FIG. 3 shows an example of processing by the recovery processing unit according to an embodiment of the invention. show.

In FIG. 1, 10 is a database, 11 is a page that is a unit of input/output in the database IO, 12 is a logical time storage area in which a logical time indicating the chronological order of updates for each page is stored, and 13 is a processing target The record that becomes
14 is a transaction processing unit that issues an access request to the database 10; 15 is an access control unit that controls access to the database 10; 16 is a log management unit that manages logs that are update history information; and 17 is a unit that temporarily stores collected logs. 18 is a log storage non-volatile storage device 819 consisting of a disk device or memory with power backup, a log containing information regarding logical time and updates, and 20 is a log buffer that is stored in the database 10 in the event of a failure. Represents a recovery processing unit that performs recovery.

Hereinafter, explanation will be given according to phases 1 to 1 shown in FIG.

■ The transaction processing unit I4 is the database 10
When updating the record 13 in the record 13, it acquires exclusive transaction rights for the record 13 and issues a record update request to the access control unit 15.

(2) The access control unit 15 updates the record 13 of the specified page 11. At this time, the logical time in the logical time storage area 12 in the page 11 is updated.

- When updating the record 13, request the log management unit 16 to collect the post-update log/pre-update log.

■ The log management unit 16 stores record 1 in the log buffer 17.
3. Accumulate post-update logs/pre-update logs for 3.

■ The processing of the transaction processing unit 14 has ended.

When committing (CO2-1t), the log management unit 16 is requested to write the log.

(2) The log management unit 16 reads the log related to the transaction processing unit 14 from the log buffer 17.

■ The read log is stored in the log storage non-volatile storage device 1.
Write it down at 8.

■ Due to main system failure or peripheral device failure.

When the database IO needs to be restored, the restoration processing unit 2
0 is called.

■ The recovery processing unit 20 uses the non-volatile storage device 1 for storing logs.
8 and sort the logs 19 according to the logical time of each log 19.

[Phase] Database 1 in the order of sorted log 19
Page 12' of 0' is restored.

FIG. 2 shows the transaction processing unit (TRN1) 14-
1 and transaction processing unit (TRN2) 14-2
shows an example in which different records (A, B) 13 in the same page 11 of the database 10 are processed. These can be processed in parallel as transactions by record exclusion. Transaction processing unit 1
4-1 inserts record A, and transaction process 'fMHz-2 updates record B to extend the record length.

After the transaction processing unit 14-1 acquires exclusive transaction rights for record A, the transaction processing unit 14-1
, and updates the logical time in the page from 1, for example, to to ti.

Then, the management information in the page 11 is changed and inserted into the record, and after the update, the page 11 is unlocked.

Also, record A is inserted into log L at logical time L1.

Collect g-A.

At the time of commit, the transaction processing unit 14-1 stores the collected log Log-A in the log storage nonvolatile storage device 18, and releases the transaction exclusion for record A.

After acquiring exclusive transaction rights for record B, the transaction processing unit 14-2 processes page 11.
, and updates the logical time in the page from 1, for example, tl to t2.

Then, the management information in page 11 is changed, and record length expansion processing for record B is performed. After that update.

Unlock page 11.

Also, update log L of record B at logical time t2.

Collect E-B.

At the time of commit, the transaction processing unit 14-2 stores the collected log Log-B in the log storage nonvolatile storage device 18, and releases the exclusion of the transaction for record B.

Logs are written to the log storage non-volatile storage device 18 in the order in which the logs 19 need to be written due to five commits, regardless of the order of operations on the pages 11. Therefore, when the processes are executed in the order of ■ to ■ shown in FIG.

The time series log data in the nonvolatile storage bag W18 for storing logs is different from the update order of the page 11. In this example, log Log-B is written out five times before log Log-A.

FIG. 3 shows an example of the processing of the recovery processing unit 20 shown in the first time.

Assume that after the update shown in FIG. 2, the database 10 becomes faulty and the recovery processing section 20 is called.

The recovery processing unit 20 reads the log 19 from the log storage non-volatile storage device 18 as shown in FIG. 3(a), and stores the log 19 in ascending order of logical time as shown in FIG. 3(b). Sort. Next, by the process shown in FIG. 3(C), pages 11 are restored in the order of the sorted logs 19. This process shown in FIG. This process is similar to the recovery process. The same applies to recovery of other pages.

As described above, by sorting time-series log data by logical time during recovery processing, the order of operations on pages can be guaranteed, and even record-by-record exclusion can be performed without deteriorating the overhead during commit. can be restored.

〔Effect of the invention〕

As described above, according to the second aspect of the present invention, performance deterioration in log management when using record-based transaction exclusion can be prevented, and recovery processing can be simplified.

[Brief explanation of drawings]

FIG. 1 shows a configuration example of the present invention. FIG. 2 is an example of log collection and storage according to an embodiment of the present invention. FIG. 3 is an example of processing by a recovery processing unit according to an embodiment of the present invention. Figure 4 is an example of the prior art. FIG. 5 shows a diagram illustrating problems with the prior art. In the figure, 10 is a database, 11 is a page, 12 is a logical time storage area, 13 is a record, 14 is a transaction processing unit, and 15 is an access control unit. 16 is a log management unit, 17 is a log buffer, 18 is a nonvolatile storage device for storing logs, 19 is a log, and 20 is a recovery processing unit.

Claims (1)

[Claims] A database management system having an exclusive control function on a record-by-record basis, wherein a logical time indicating the chronological order of updates is
In a log management/recovery processing method in a system that recovers database pages in the event of a failure based on logical time by storing them in database pages and logs, when a transaction is completed, the log is stored in the order of transaction completion. A log management means (16) for writing to a non-volatile storage device and managing it; and a log management means (16) that, when a database is restored, sorts the logs written to the non-volatile storage device in order of logical time, and writes the logs in the database in the order of the sorted logs. A log management/recovery processing method comprising a recovery processing means (20) for restoring a page of.