JP6376947B2 - Virtual database system management apparatus, management method, and management program - Google Patents

Description

  The present invention generates a subquery to be executed in each database system in response to a query from a user in an environment where a plurality of database systems exist, and the remaining query is based on the result of each subquery. The present invention relates to a virtual database system management apparatus, a management method, and a management program that improve the efficiency of processing when the above processing is executed.

  A data virtualization system (or a multi-database system), for example, as shown in Patent Documents 1 to 4, each database is used to virtually show a plurality of database systems with different interfaces and data management methods as one database system. Data that the system has is logically integrated and managed, subquery statements are output to the database system corresponding to the given query statement, and the processing results of the subquery statements executed in each database system are collected centrally. , A system that outputs the result by integrating them into one according to a virtual schema (defining a process for converting an actual physical table into a logical table provided to a user).

  These data virtualization systems basically connect to multiple database systems and manage multiple databases as physical database models, while creating logical database models and associating them with physical database models. The physical database model is handled as one logical database model, and a query statement can be executed on the logical database model.

JP 09-091309 A Japanese Patent Laid-Open No. 10-307743 Special table 2013-508857 gazette Japanese Patent Application No. 2014-057080

In the above-described virtual database system, a subquery sentence that can be executed in each database system connected to the virtual database system is generated and issued for a query sentence given by a user, and the processing result of the subquery sentence is virtualized. The database system receives and executes the remaining processing of the query statement and returns the result to the user.
However, when executing the remaining processing of the query statement, depending on the result of the sub-query statement executed in each database system, the amount of data to be processed in the virtual database system becomes enormous and the processing time becomes long, or the resource is insufficient There is a problem that the process may not be completed and may end abnormally.

  The present invention has been proposed in view of the above circumstances, and in the environment of a virtual database system management apparatus in which a plurality of database systems exist, when generating a subquery for each database system from a query, It is an object of the present invention to provide a virtual database system management apparatus, a virtual database system management method, and a virtual database system management program that realize processing efficiency by arrangement and query statement conversion associated therewith.

  To achieve the above object, the present invention provides a virtual database system management apparatus in an environment that handles a plurality of database systems, by generating an execution plan in consideration of the execution result size of a subquery statement. Make query processing more efficient.

That is, claim 1 is characterized in that a virtual database system management apparatus to which a plurality of database systems are connected and data is output according to an inquiry from a user system has the following configuration.
A query statement generation unit that performs generation of a subquery statement and conversion of the query statement accompanying data rearrangement by the subquery statement in the database system unit.
An execution result estimation unit that estimates an execution result size of the subquery generated by the query statement generation unit.
The execution order of the subquery statement and the converted query statement based on the execution result size estimated by the execution result estimation unit and the subquery statement for the subquery statement generated by the query statement generation unit and the converted query statement Query input analysis unit that determines the data layout of the execution results.
A query execution unit that executes the subquery statement and the converted query statement based on the execution order determined by the query input analysis unit;
Further, physical database management information for managing entry numbers associated with the database system and logical database information to be queried from the user system are defined, and each entry number corresponding to the physical database management information is defined. A database management unit storing logical database management information for managing and linking
The query input analysis unit updates the logical database management information by determining the execution order of the subquery statements and the data arrangement of the execution results,
The query input analysis unit
In response to a query statement from the user system, a plurality of single database subquery statements that are closed in each database of each database system are generated, and an execution result size estimated from each single database subquery statement is determined in advance. A function to align them in an order distinguished by “sufficiently large” and “substantially equal” according to the determined criteria,
A plurality of database subquery statements that are closed by a plurality of databases of each of the database systems in the query statement when one or more “sufficiently large” exist in the alignment result of the execution result size,
When the execution result size estimated from the single database subquery statement is “sufficiently large” with respect to the execution result size estimated from the multiple database subquery statement,
A function for adding a table linked to an execution result of a single database subquery statement for a single database subquery statement whose execution result size is not sufficiently large to a database corresponding to a sufficiently large execution result size of the logical database management information; Prepared,
The inquiry execution unit
It is characterized in that it has a function of performing data rearrangement for adding a table that is an execution result of the single database subquery statement to the physical database management information based on the execution order determined by the query input analysis unit.

Claim 2 is the virtual database system management apparatus according to claim 1 ,
The “sufficiently large” is a case where the difference in the execution result size is two or more digits,
The “substantially equal” is characterized in that the difference in the execution result size is one digit or less.

Claim 3 is a virtual database system management method in which a plurality of database systems are connected and data is output in response to a query statement from a user system.
Physical database management information for managing entry numbers associated with the database system and logical database information to be queried from the user system are defined, and the corresponding entry numbers are linked to the physical database management information. A procedure for storing logical database management information to be attached and managed,
In response to a query statement from the user system, a plurality of single database subquery statements that are closed in each database of each database system are generated, and an execution result size estimated from each single database subquery statement is determined in advance. In the query statement when there is one or more “sufficiently large” in the alignment result of the execution result size, with the function of aligning in the order distinguished by “sufficiently large” and “approximately equal” according to the specified criteria A plurality of database subquery statements that are closed in a plurality of databases of each database system are generated, and an execution result size estimated from the single database subquery statement is equal to an execution result size estimated from the plurality of database subquery statements If the result size is sufficiently large, A table linked to the execution result of the single database subquery statement for the single database subquery statement is added to the database corresponding to the sufficiently large execution result size of the logical database management information, while the execution order of the subquery statements And a procedure for determining the data arrangement of the execution result and updating the logical database management information;
A procedure for performing data relocation to add a table that is an execution result of the single database subquery statement to the physical database management information based on the execution order determined by the query input analysis unit;
It is characterized by including.

A virtual database system management method according to a fourth aspect is characterized in that each procedure according to the third aspect is repeated until the unit of the database system becomes one.

Claim 5 builds each part according to claim 1 on a computer, estimates an intermediate data size at the time of executing a query statement, determines an appropriate data arrangement between database systems, and inquires according to the data arrangement It is a virtual database system management program that performs processing for generating an execution plan by changing a sentence.

  According to the present invention, when a subquery statement for each database system is generated from a query statement in a virtual database system management apparatus in an environment where a plurality of database systems exist, the execution result size (intermediate data size) of each subquery statement is generated. ) To determine the appropriate data placement between database systems, and change the query statement according to the data placement to generate an execution plan, improving the query statement processing efficiency in the virtual database system management device Can be made.

It is a block diagram which shows the structure of the virtual database system management apparatus of this invention. It is a flowchart figure which shows the process sequence in an inquiry input analysis part. It is a model figure which shows the data retention condition in a virtual database system (two database systems). 4 is a data diagram of an inquiry sentence Q. FIG. It is a data figure of subquery sentence Qa. It is a data figure of subquery sentence Qb. It is a data figure of subquery sentence Qab. It is a model figure which shows the data retention condition (at the time of TBL_Qb addition) in a virtual database system. It is a data diagram of a new query sentence Q. It is a model figure which shows the data holding condition (at the time of TBL_Qb addition and a logical table association) in a virtual database system. It is a model figure which shows the data retention condition in a virtual database system (three database systems). It is a data figure of subquery sentence Qa. It is a data figure of subquery sentence Qb. It is a data figure of subquery sentence Qc. It is a data figure of subquery sentence Qab. It is a model figure which shows the data retention condition (at the time of TBL_Qb addition) in a virtual database system. It is a data diagram of a new query sentence Q. It is a data figure of subquery sentence Qa. It is a data figure of subquery sentence Qc. It is a model figure which shows the data retention condition (TBL_Qa addition) in a virtual database system. It is a data diagram of a new query sentence Q.

An example of an embodiment of a virtual database system management apparatus of the present invention will be described with reference to the drawings.
The virtual database system is a system that enables execution of query contents by selecting a database system according to the query contents of the user in an environment where a plurality of database systems having the same data exist, as shown in FIG. The system includes a user system 1 on which a user posts an inquiry, a virtual data system management device 2, and one or more database systems 3 used by the virtual data system management device 2. The user system 1, the virtual data system management device 2, and the database system 3 are connected via a network. The virtual data system management device 2 is constructed on a computer by installing it by downloading software via a recording medium storing a virtual database system management program or the Internet.

The computer in which the virtual database system management apparatus is constructed includes a ROM that stores a basic program including an operating system (OS) and various basic devices, a hard disk drive (HDD) that stores various programs and data, A media drive device that reads programs and data from a storage medium such as a CD-ROM or DVD, a CPU that executes the programs, a RAM that provides a work area for the CPU, and an input / output interface (I / F) A general configuration mainly includes a pointing device such as a display, a keyboard and a mouse, and a parallel / serial I / F communicating with an external device.
In the virtual database system management apparatus 2 of the present embodiment, a virtual database system management program is input from a serial / parallel I / F or read by a media drive device and stored in advance in an HDD. The virtual database system management program is stored in a storage medium, read by the media drive device, and installed in the HDD.

  A virtual database system management device 2 constructed on a computer defines logical database information (database, table) to be accessed by a user in an environment where a plurality of database systems 3 exist, and each database Assign one or more database management systems, databases, and table sets in the system.

  The user system 1 transparently acquires query statement processing results for a plurality of database systems 3 by posting a query statement using an integrated data model provided by the virtual database system management device 2.

  The database system 3 includes a database 31 that actually stores data and a database management system 32 that provides processing for the data. The database system 3 provides processing for data on the database 31 via an interface of the database management system 32.

  The virtual database system management device 2 includes a database interface unit 21 connected to a plurality of database systems 3, a database management unit 22 that acquires and manages information of each database system 3 via the database interface unit 21, and a query statement generation A user interface unit 23 that inputs / outputs from / to the user system 1, a query input analysis unit 24 that analyzes a query statement from the user system 1, and a subquery statement from the query statement to each database system 3. A query statement generation unit 25 that performs generation, an execution result estimation unit 26 that estimates an execution result size of a subquery statement, an execution plan generation unit 27 that generates an execution plan of a series of subquery statements, and a subquery statement And an inquiry execution unit 28.

  The database management unit 22 defines a physical database management table 221 for managing entry numbers associated with the database 31 and logical database information to be accessed from the user system 1. For the data in the physical database management table 221, Information of each database system 3 is managed by providing a logical database management table 222 that links and manages corresponding entry numbers.

An example of linking between data in the physical database management table 221 and the logical database management table 222 is shown in FIG.
Two databases 31 (Da and Db) are connected to the virtual database system management apparatus 2, the database Da has a table lineitem, and the database Db has tables customer and orders.
In the physical database management table 221, entry numbers (P1 to P3) for association, database type (Da or Db), and table type (lineitem, customer, orders) in the database are managed as database information. . In the logical database management table 222, logical database information (database, table) to be accessed from the user system 1 is managed, and information managed by linking each corresponding entry number to the data of the physical database management table 221. Link items (P1 to P3) are set.

  The query input analysis unit 24 analyzes the syntax of the query sentence input via the user interface unit 23 and outputs the analysis result to the execution plan generation unit 27. Further, the query input analysis unit 24 determines the execution order of the sub-query sentence and the data arrangement of the execution result of the sub-query sentence with respect to the query sentence input from the user system 1 during the syntax analysis of the query sentence. Processing in the query input analysis unit 24 regarding determination of execution order and determination of data arrangement will be described later.

The query statement generation unit 25 is called from the query input analysis unit 24, generates a subquery statement (single database subquery statement) in units of database, and converts a query statement accompanying data rearrangement by the subquery statement.
The execution result estimation unit 26 is called from the query input analysis unit 24 and estimates the execution result size of a given subquery.
The execution plan generation unit 27 generates an execution plan for a series of query statements (query statements converted into sub-query statements) determined by the query input analysis unit 24.

  The query execution unit 28 executes the execution plan generated by the execution plan generation unit 27, executes the subquery statement via the database interface unit 21, and sends the execution result to the user system 1 via the user interface unit 23. Output.

  Next, in the virtual database system management apparatus 2, the detailed processing (virtual database system management method) in the query input analysis unit 24 for the query text input from the user system 1 via the user interface unit 23 is shown in the flowchart of FIG. Will be described with reference to FIG.

First, a query sentence input from the user system 1 is set as Q, a database system list constituting the query sentence Q is set as {Di}, and a query sentence list is set as {} (step 101). The database system list includes elements of the database 31 connected to the virtual database system management apparatus 2. The query statement list is initially an empty set.
It is determined whether or not the number i of elements in the database system list {Di} is greater than 1 (step 102).
If the number of elements i is greater than 1, for each element Di in the database system list {Di}, the query statement generator 25 generates a single database subquery statement Qi corresponding to Di in the query statement Q (step 103). “Corresponding to Di in Q” means a selection / projection / join operation that is closed to Di in the query sentence Q.

Next, the execution result size Si of Qi is estimated from the execution result estimation unit 26 for each element Qi of {Qi} (step 104). The execution result size need only be known and need not be exact.
The elements of the execution result size {Si} are aligned in the order of “>> (sufficiently large)” and “≈ (approximately equal)” (step 105). Therefore, A >> B means “A is sufficiently larger than B”, and A≈B means “A is almost equal to B (A >> B or B >> A is not)”.
Note that “>> (sufficiently large)” and “≈ (approximately equal)” are classified according to a predetermined criterion. For example, “>> (sufficiently large)” means that the execution result size is 1 MB or more and a difference of about two digits. For example, when one execution result size is 1 MB and the other execution result size is 100 MB, it is determined to be “sufficiently large”. If the execution result sizes are smaller than 1 MB or the difference in execution result size is one digit or less, the result is classified as “substantially equal”.
Depending on the execution result size, “>> (sufficiently large)” may mean a difference of about 3 digits, and “approximately equal” may mean a difference of 2 digits or less.

  As a result of arranging the execution result sizes Si of the elements Qi, it is determined whether or not one or more “>>” exists between Si (step 106).

If there are one or more “>>” in the Si alignment result, one of the top elements is selected as Sa. The following processes (1) to (3) are executed for all Sb satisfying Sa >> Sb (step 107).
(1) A plurality of database subqueries corresponding to the database Da and the database Db in the query sentence Q by the query sentence generation unit 25 (only for selection / projection / join operations closed to Da and Db in the query sentence Q) A sentence Qab is generated.
(2) The execution result estimation unit 26 estimates the execution result size Sab of the multiple database subquery statements Qab.
(3) If Sa >> Sab, “Qb → a” is added to the query statement list {}. “Qb → a” means that the execution result of the single database subquery Qb in the database Db is added to the database Da, and an item is added to the logical database management table 222 of the database management unit 22.

  The database Db for all elements in the query statement list is deleted from the database system list {Di}, and the query statement generator 25 generates a query statement corresponding to {Di} in the query statement Q (data relocation by subquery statement) Conversion of the inquiry sentence associated with the new inquiry sentence Q) (step 108). “Corresponding to {Di} in the query sentence Q” means that the query sentence Q is rewritten with only the elements of {Di}.

  If there is no “>>” in the Si alignment result in step 106, or if the number i of elements in {Di} is 1 in step 102, the query statement for each element Di in the database system list {Di} The generation unit 25 generates a subquery sentence Qi corresponding to Di in the query sentence Q and a query sentence Qv to be executed on the virtual database system after executing all the subquery sentences Qi and adds them to the query sentence list (step 109). ). However, when the number of elements of {Di} is 1, Qi = Q and only Q is added to the query statement list.

  In the following, specific processing in the query input analysis unit 24 in FIG. 1 is performed when there are two database systems 3, taking Q3 of the TPC-H benchmark (one of 22 types of TPC-H benchmarks) as an example. An example (embodiment 1) and an embodiment (embodiment 2) when there are three database systems 3 will be described.

Example 1
FIG. 3 shows the configuration of the physical database management table 221 and the logical database management table 222 of the database management unit 22 in the virtual database system management apparatus 2. FIG. 4 shows a query sentence Q input from the user system 1. The database system list is {Da, Db}, which is the type of database connected to the virtual database system management apparatus 2.

The single database subquery statements Qa and Qb for the database Da or the database Db in step 102 are respectively decomposed so that each database can be executed on the query statement Q of FIG.
Assume that the relationship of Sa >> Sb holds when the execution result sizes of the single database subquery statements Qa and Qb are estimated as Sa and Sb in step 103. When the relationship of Sa >> Sb is established, the execution result of the subquery sentence Qa is sufficiently larger than that of the subquery sentence Qb, which indicates that it can become a bottleneck in the processing of the virtual database system management apparatus 2.

The multi-database subquery sentence Qab corresponding to the databases Da and Db generated in step 107 is as shown in FIG. Assume that the relationship of Sa >> Sab holds when the execution result size of the subquery Qab is estimated to be Sab.
When the relationship of Sa >> Sab holds, the execution result size of the multiple database query statements that target the databases Da and Db is sufficiently smaller than the result of the single database query statement that targets only the database Da. The burden on the virtual database system management apparatus 2 can be greatly reduced by moving the result of the single database subquery sentence Qb to the database Da and executing the plurality of database subquery sentences Qab.

When the relationship of Sa >> Sab is satisfied, the query statement list is {Qb → a}, and the execution result “TBL_Qb” of the single database subquery statement Qb is added to the database Da. When “TBL_Qb” is added to the table, the result is as shown in FIG.
The database system list is updated from the query statement list to become {Da}, and the new query statement Q (Q1) is as shown in FIG. 9, and data is acquired only from the database Da.

  Returning to the beginning of the processing flow of FIG. 2 (step 102), since the elements of the database system list are not larger than 1, finally the query statement list is added with Q1 to become {Qb → a, Q1} (step 109). Then, the processing of the inquiry input analysis unit 24 is finished. The query statement list {Qb → a, Q1} is executed in the execution order according to the execution plan of executing Qb, adding this execution result to Da, and executing Q1.

  Based on the generated query statement list, the execution plan generation unit 27 formulates an execution plan and the query execution unit 28 executes the execution plan. The query execution unit 28 adds a table to the corresponding database system Da as shown in FIG. 10 and adds a physical database management table of the database management unit 22 when it is necessary to add a table such as “Qb → a”. 221 and the corresponding information in the logical database management table 222 are updated. The added table can be deleted when the execution of the query process is completed.

(Example 2)
Next, the processing outline in the query input analysis unit 24 in FIG. 1 will be described for a case where there are three database systems 3. As for the query sentence Q inputted from the user system 1, the same one shown in FIG. 4 as in the first embodiment is used.

FIG. 11 shows the configuration of the physical database management table 221 and the logical database management table 222 of the database management unit 22 in the virtual database system management apparatus 2. Let the database system list be {Da, Db, Dc}.
The single database sub-query statements Qa, Qb, and Qc for the database Da, Db, or Dc in step 102 are respectively decomposed for each database with respect to the query statement Q of FIG. 4 to become FIGS. 12, 13, and 14, respectively. .

Assume that the relationship Sa≈Sc >> Sb holds when the execution result size of the single database subquery Qa, Qb, or Qc is estimated to be Sa, Sb, Sc in step 103.
The multiple database subquery statement Qab in step 107 is as shown in FIG. 15, and when the execution result size of the multiple database subquery statement Qab is Sab, the relationship of Sa >> Sab is established.

The query statement list is {Qb → a}, and “TBL_Qb” is added to the database Da in the logical database management table 222 to add the execution result of the single database subquery Qb to the database Da, as shown in FIG. .
The database system list is updated from the query statement list, Db is deleted as {Da, Dc}, and the new query statement Q (Q1) is as shown in FIG.

Returning to the beginning of the processing flow of FIG. 2 (step 102), similarly, the single database subquery statements Qa and Qc for the databases Da and Dc are respectively shown in FIGS. 18 and 19, and the single database subquery statements Qa and Qc are executed. It is assumed that the relationship Sc >> Sa is satisfied when the result size is Sa and Sc.
The query statement list is {Qb → a, Qa → c}, and “TBL_Qa” is added to the database Dc of the logical database management table in order to add the execution result of the single database subquery Qa to the database Dc. It becomes like this.
The database system list is updated from the query statement list, Da is deleted {Dc}, and the new query statement Q (Q2) is as shown in FIG.

  Returning again to the beginning of the processing flow of FIG. 2 (step 102), since the elements of the database system list are not greater than 1, the query statement list finally adds the query statement Q2, {Qb → a, Qa → c , Q2}, and the processing of the query input analysis unit 24 is finished.

  As described above, with respect to the query statement Q, the query result in the database Db is moved to the database Da, the query result in the database Da is then moved to the database Dc, and finally the remaining query processing is executed in the database Dc. As a result, the amount of data transferred between the virtual database system management apparatus 2 and each database system 3 can be greatly reduced, and as a result, the processing time can be expected to be greatly reduced.

According to the above-described virtual database system management device, management method, and management program, when there are a plurality of database systems 3 and they are handled in an integrated manner, the virtual database system has become a bottleneck in the conventional virtual database system Part of the exchange of large amounts of data between the management apparatus 2 and each database system 3 can be eliminated.
As a result, the query processing in the virtual database system management apparatus 2 is made more efficient, and it is possible to avoid the situation where the process takes a long time or the situation where the process ends abnormally due to a lack of resources, and the query result can be obtained. It becomes possible.

  DESCRIPTION OF SYMBOLS 1 ... User system, 2 ... Virtual database system management apparatus, 3 ... Database system, 21 ... Database interface part, 22 ... Database management part, 23 ... User interface part, 24 ... Query input analysis part, 25 ... Query sentence generation part, 26 ... Execution result estimation unit, 27 ... Execution plan generation unit, 28 ... Query execution unit, 31 ... Database management system, 32 ... Database, 221 ... Physical database management table, 222 ... Logical database management table

Claims (5)

In a virtual database system management apparatus in which a plurality of database systems are connected and data is output according to an inquiry from a user system,
A query statement generation unit for generating a subquery statement in the database system unit and converting the query statement accompanying data relocation by the subquery statement;
An execution result estimation unit for estimating the execution result size of the subquery generated by the query statement generation unit;
The execution order of the subquery statement and the converted query statement based on the execution result size estimated by the execution result estimation unit and the subquery statement for the subquery statement generated by the query statement generation unit and the converted query statement A query input analyzer that determines the data placement of the execution results;
A query execution unit that executes the subquery and the converted query statement based on the execution order determined by the query input analysis unit;
Physical database management information for managing entry numbers associated with the database system and logical database information to be queried from the user system are defined, and the corresponding entry numbers are linked to the physical database management information. And a database management unit storing logical database management information to be managed,
The query input analysis unit updates the logical database management information by determining the execution order of the subquery statements and the data arrangement of the execution results,
The query input analysis unit
In response to a query statement from the user system, a plurality of single database subquery statements that are closed in each database of each database system are generated, and an execution result size estimated from each single database subquery statement is determined in advance. A function to align them in an order distinguished by “sufficiently large” and “substantially equal” according to the determined criteria,
A plurality of database subquery statements that are closed by a plurality of databases of each of the database systems in the query statement when one or more “sufficiently large” exist in the alignment result of the execution result size,
When the execution result size estimated from the single database subquery statement is “sufficiently large” with respect to the execution result size estimated from the multiple database subquery statement,
A function for adding a table linked to an execution result of a single database subquery statement for a single database subquery statement whose execution result size is not sufficiently large to a database corresponding to a sufficiently large execution result size of the logical database management information; Prepared,
The inquiry execution unit
A function of performing data relocation for adding a table, which is an execution result of the single database subquery statement, to the physical database management information based on an execution order determined by the query input analysis unit. A virtual database system management device. The “sufficiently large” is a case where the difference in the execution result size is two or more digits,
The “substantially equal” is a case where the difference in the execution result size is one digit or less.
The virtual database system management apparatus according to claim 1 . In a virtual database system management method in which a plurality of database systems are connected and data is output according to a query statement from a user system,
Physical database management information for managing entry numbers associated with the database system and logical database information to be queried from the user system are defined, and the corresponding entry numbers are linked to the physical database management information. A procedure for storing logical database management information to be attached and managed,
In response to a query statement from the user system, a plurality of single database subquery statements that are closed in each database of each database system are generated, and an execution result size estimated from each single database subquery statement is determined in advance. In the query statement when there is one or more “sufficiently large” in the alignment result of the execution result size, with the function of aligning in the order distinguished by “sufficiently large” and “approximately equal” according to the specified criteria A plurality of database subquery statements that are closed in a plurality of databases of each database system are generated, and an execution result size estimated from the single database subquery statement is equal to an execution result size estimated from the plurality of database subquery statements If the result size is sufficiently large, A table linked to the execution result of the single database subquery statement for the single database subquery statement is added to the database corresponding to the sufficiently large execution result size of the logical database management information, while the execution order of the subquery statements And a procedure for determining the data arrangement of the execution result and updating the logical database management information;
A procedure for performing data relocation to add a table that is an execution result of the single database subquery statement to the physical database management information based on the execution order determined by the query input analysis unit;
A virtual database system management method comprising: 4. A virtual database system management method in which each procedure according to claim 3 is repeatedly performed until the number of database system units becomes one.   Each part according to claim 1 is constructed on a computer, an intermediate data size is estimated at the time of executing a query statement, an appropriate data arrangement between database systems is determined, and the query sentence is changed according to the data arrangement A virtual database system management program that performs processing to generate an execution plan.