JPH11306063A - High reliability database management system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a database management system high in reliability. SOLUTION: This system is provided with plural servers 110, 120 and 130 provided with storage units 112, 122 and 132 where the same databases are mutually stored and clients 210, 220 and 230 which demand execution of a structured query language(SQL) of the plural servers 110, 120 and 130. Each of the servers 110 to 130 returns the execution result of the SQL to the client and the clients 210 to 230 demand execution of the next SQL of the server when responses from all the servers are the same. When responses from more than one server are different from others, the clients 210 to 230 demands the execution of the SQL once again. Thus, reliability of a database system is improved and it is possible to maintain the database of all the servers 110, 120 and 130 in the same way.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a database management system, and more particularly to a database management system capable of improving reliability.

[0002]

2. Description of the Related Art Hitherto, a client / server type database management system capable of referring to and updating a database stored in a server from a plurality of clients has been used. As a server used in such a database management system, a high-speed processing speed and a high reliability are required, and therefore, an expensive large-sized computer is generally used.

In recent years, the performance of inexpensive processors for personal computers has been dramatically improved, and processing speeds equivalent to or larger than those of conventional large computers have been developed. Therefore, an inexpensive personal computer can be used as a server of a database management system.

[0004]

However, when such an inexpensive personal computer is used as a server of a database management system, if the same operation is performed, reproducible troubles that cause the same trouble every time will be hardened. Although it is possible to completely solve the problem by using hardware or software, problems such as abnormalities in the data in the storage medium due to static electricity or errors in checking the memory, such as errors in the environment, can be easily achieved. It cannot be reduced and cannot be completely prevented.
When the database becomes illegal contents due to such a problem, there is a problem that the database may be left unnoticed and become a serious obstacle. In order to reduce defects and improve reliability more than a certain level, it was very costly.

[0005] In order to improve the reliability of a database management system, a system in which a database is stored in a plurality of servers is known. Conventionally, the database is distributed to a plurality of servers to reduce the risk in the event of a failure, but it has not been possible to prevent the occurrence of the above-mentioned problems. It is conceivable to store the same database on multiple servers, but when multiple servers receive updates from multiple clients at the same time, the order of receiving commands from clients is different, and the same database is stored between multiple servers. There is a problem that the property may not be maintained. When communicating or exchanging data between servers to keep the contents of the database of each server the same, if one server stops due to an error, the other servers are affected and stopped There is a problem that the effect of improving the reliability is small because of the fear.

An object of the present invention is to provide a high-reliability database management system capable of solving the above-mentioned problems and greatly improving reliability.

[0007]

A high reliability database management system according to claim 1 of the present invention, a method for executing processing of a high reliability database according to claim 4 or claim 7 of the present invention.
According to the high reliability database program described in the server returns the processing result of the data processing command to the client, the client determines whether all of the processing results returned from the plurality of servers are the same, When at least one of the processing results returned from the plurality of servers is different from the processing result returned from another server, the client terminates the processing of the data processing instruction, returns to the state before execution, and then re-executes the data processing instruction. Requests to be executed are made to all of the multiple servers. Therefore, as long as the same trouble does not occur in all servers, the data processing command can be correctly executed. Therefore, when a system failure rate of one server is S, by using the n number of servers, the entire system failure of the entire server system can be substantially close to S ⁿ becomes 0.

According to a second aspect of the present invention, there is provided a high-reliability database management system, a high-reliability database processing method according to the fifth aspect, and a high-reliability database program according to the eighth aspect. If there is a server where the processing result of the data processing command requested by the server is not returned within a predetermined time, the processing by the data processing command is terminated, and after returning to the state before the execution, the request for the execution of the data processing command is transmitted to a plurality of servers. Since the process is re-executed for all, the client can be prevented from stopping for a long time waiting for a response from the server.

According to a third aspect of the present invention, there is provided a high reliability database management system, a high reliability database processing method according to the sixth aspect, and a high reliability database program according to the ninth aspect. When the re-execution of the processing command has reached the specified number of times, the processing by the transaction including the data processing command is terminated and the state before execution is returned, so that the client does not repeat the request to re-execute the data processing command indefinitely it can.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram showing a high reliability database management system of the present invention. The database management system (DBMS: DataBase Managem) of this embodiment
ent System) is composed of a client / server system.

The plurality of servers 110, 120, 130
Storage devices 112, 122, and 132 that store independent and identical databases, and processing units 111, 121, and 13 that perform reference and update processing on the databases.
1 is provided. The servers are not physically connected to each other, and the servers do not transmit and receive data. The plurality of clients 210, 220, and 230 are connected to each of the servers 110, 120, and 130 by a communication line so that data can be transmitted and received.

The servers 110, 120 and 130 and the clients 210, 220 and 230 are provided with a central processing unit (C).
PU), a main storage device (RAM), an auxiliary storage device (hard disk), an input device (keyboard, mouse, etc.), and an output device (monitor, printer, etc.)
And a computer program. This computer program is a floppy disk (FD),
It is provided by being recorded on a computer-readable storage medium such as a CD-ROM, a magneto-optical disk (MO), and is installed on a hard disk of the computer.
It is read and executed on the AM. Further, the program may be provided on a network such as the Internet, and the program may be recorded in a place remote from the computer to be executed.

The user of the database is the client 21
The input devices 0, 220, and 230 are operated to refer to and update the databases of the servers 110, 120, and 130. FIG. 2 shows the database 10
It is a schematic diagram which shows the structure of. In the database 10,
A plurality of tables 11 are included. In this embodiment, the table 11 is divided into pages 12 each having a fixed-length data structure. The page 12 includes a plurality of rows 13 serving as records of the database 10. The row 13 includes a plurality of columns (not shown) serving as the contents of the fields of the database 10. These tables 11, pages 12, rows 13, columns, and the like are referred to as resources to be processed by the database 10.

The period from when the client 210, 220, 230 logs in to the database of the server 110, 120, 130 until it logs out is called one processing session. One processing session is composed of one or more transactions, and a maximum of one transaction can be executed at a time. The transaction commits (co
It is the smallest logical execution unit that can be mmit or rollback. One transaction is composed of one or a plurality of SQL (Structured Query Language).
) And the like.

Taking a cash dispenser of a bank as an example, one processing session is from the start-up of a terminal in the morning to the end in the evening, and operations such as user's deposit and transfer are performed in one transaction. Corresponding. For example, in the case of transfer from one account to another account, it is necessary to perform a process to decrease the amount of one account and a process to increase the amount of the other account. (Commit), or neither (abort).

The client has a function of a user interface (UI), and accepts a data operation in a format that is easy for the user to understand, and can convert the data operation into SQL. When execution of a transaction is started by a user operation, the clients 210, 220,
230 requests each of the servers 110, 120, and 130 to execute SQL constituting a transaction.

As shown in FIG. 1, SQL commands issued from a plurality of clients are input queues 113 and 12 which are first-in first-out storage areas provided in each server.
3 and 133. Processing means 111, 121, 1
The SQL module 31 receives the SQL, converts it into an input / output operation for the physical storage devices 112, 122, and 132 while performing control such as optimization, concurrent execution control, failure recovery, and safety. SQLM), and sequentially reads out SQL commands from the input queues 113, 123, and 133, and executes processing in SQL units. A plurality of processing sessions can execute a transaction in parallel for one database.

The processing means 111, 121, and 131 of the servers 110, 120, and 130 copy the requested SQL processing target resources from the databases in the storage devices 112, 122, and 132 to a work area provided for each session. , The SQL processing is performed on the work area.
At the request of the client, the server can abort the processing performed by the SQL on the work area and return it to the state before execution (rollback), that is, invalidate the processing by the SQL.

Processing means 111, 12
The processing results of the SQL executed by the programs 1 and 131 are stored in the output queues 114, 124 and 134, and are sequentially returned to the clients that have requested the execution. On the client, SQ
All servers 110, 120, and 13 that have requested the execution of L
Compare the responses from 0.

If the SQL is for reference,
Each server returns the contents of the referenced resource as a processing result. The client compares the returned data itself and determines whether or not all the data match. If the SQL is for a column update, the client compares the data sent from each server to determine if all match.

If the SQL is for deletion,
The client compares the data transmitted from each server and determines whether or not all match. If the SQL is related to insertion, it is only necessary to know that each insertion request has been completed normally. If the client determines that the processing results returned from all the servers 110, 120, and 130 are the same, the client can request the server to execute the next SQL.

The server 110, 12 for one SQL
If any one of the processing results returned from 0, 130 is different, the client sends a request to roll back the processing performed by the SQL to all servers 110, 120, 13
0, and re-execute the SQL. The server rolls back the processing performed by the SQL, and then executes the SQL again. Therefore, the server 11
Even if a failure occurs in any of 0, 120, and 130, and the illegal processing is performed, if the correct processing is performed on another server, the client sends a message to all the servers 110, 120, and 130. SQL execution is requested again, and the process is repeated until the same result is obtained. As long as the same failure does not occur in all servers, correct processing can be performed. Therefore, when the system failure occurrence rate when one server is S and the number of servers is n, the entire server base system System failure rate is almost S
ⁿ becomes closer to 0, and the reliability can be greatly improved. One of the servers, for example, the server 110
Even if a failure occurs in the server 110, the server 110 is disconnected from the clients 210, 220, and 230, and a request to execute the SQL from the clients 210, 220, and 230 is made to the servers 120 and 130 so as to perform the setting. Thus, the processing of referring to and updating the database can be continued.

The input queue 11 is also provided by the server.
3, 123, and 133, the order of receiving SQL may be different. For example, in the server 110 and the server 120, the SQ of the processing session A by the client 210
L, SQ of processing session B by client 220
L are stored in the input queues 113 and 123 in order, and the server 130 may store the SQL in the processing session B and the SQL in the processing session A in the input queue 133 in this order. In this case, if the processing target resource of the processing session A overlaps with the processing target resource of the processing session B, the server 110 or 120 sends to the client 210 the SQL of the processing session A before executing the SQL of the processing session B. Is returned and the server 130
From client 210 to SQ of processing session B
The processing result of the SQL of the processing session A after the execution of L is returned, and the processing result may be different. In the present embodiment, in the above case, all servers 1
SQ of processing session A for 10, 120, 130
After the processing by L is rolled back, execution of SQL is requested again, and S
QL and SQL of processing session A are executed in this order. Therefore, all the servers 110, 120, 13
0, the contents of the database are the same, and the same processing result is returned to the client 210.

While one processing session is executing processing on a processing target resource, locking is performed so that another processing session cannot access it. When an attempt is made to execute an SQL process for a locked processing target resource, a wait process is performed until the lock on the processing target resource is released, and the SQL is executed after the lock is released. If the order in which SQLs are accepted differs from server to server, the order in which the resources to be processed are locked changes. Therefore, if the resources to be processed in SQL are not locked by one server but locked by another server, Returning the processing result from the client to the client may be delayed. For example, if there is a server that has not responded within a predetermined waiting time after receiving a response from one server for the SQL requested by the client, the client issues a request to roll back the processing performed by the SQL. All servers 11
0, 120, and 130, and request re-execution of the SQL. The above waiting time can be set by the user.

If the re-execution of SQL is repeated N _S times or more due to a server having no response within the predetermined waiting time, the transaction including the SQL is rolled back. The number N _{S of} re-executing the above SQL can be set by the user. When the transaction commits, the contents of the work area are recorded in the database, and when the transaction aborts, the contents of the database remain unchanged.

FIG. 3 is a flowchart showing a procedure for operating a database by the database management system of this embodiment. In step S101, execution of a transaction is instructed by the user operating the client 210, for example. In step S102, the plurality of servers 11 are executed so that the client 210 executes one of the SQLs constituting the transaction.
Request each of 0, 120 and 130. Step S
In 103, the servers 110, 120, and 130 execute the SQL requested by the client on the processing target resources copied to the work area. In step S104, the client 2 is sent from the server 110, 120, or 130.
10 to return the SQL processing result.

In step S105, the client 21
0 determines whether the processing results returned from the servers 110, 120, and 130 are all the same. Each server 1
If at least one of the processing results returned from 10, 120, and 130 is different, the process proceeds to step S106, and if the number of SQL rollbacks is smaller than a predetermined number, the SQL
Is rolled back, and the process returns to step S102 to execute SQL again. If the SQL rollback count is equal to or greater than the predetermined count in step S106, the transaction is rolled back in step S108, and the transaction is aborted. The number of rollbacks is set to 0 before SQL is first executed in step S102, and the number of rollbacks is added each time the rollback is performed in step 107. In step 105, regarding the SQL requested by the client 210, when there is no response from all the other servers within a predetermined waiting time after the response is first received from one server, it is the same as when the processing results are different. In step S106, the same process is performed.

If it is determined in step S105 that the processing results returned from the respective servers are all the same, the process proceeds to step S109, and if the SQL is the last SQL in the transaction, the transaction proceeds to step S111. And writes the processing result by SQL in the work area to the database, and terminates the execution of the transaction. In step S109, the last SQ
If it is determined that it is not L, the next SQL is executed in S110.
Is executed and the process returns to step S102, and the client requests execution of SQL.

In the above embodiment, a database management system including three servers in which databases having the same contents are recorded has been described. However, the number of servers may be two or four or more.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an outline of a high reliability database management system according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a structure of a database by the database management system according to the embodiment of the present invention.

FIG. 3 is a diagram showing a flowchart of a procedure for executing processing by the database management system according to the embodiment of the present invention.

[Explanation of symbols]

 110 server 111 processing means 112 storage device 113 input queue 114 output queue 120 server 121 processing means 122 storage device 123 input queue 124 output queue 130 server 131 processing means 132 storage device 133 input queue 134 output queue 210 client 220 client 230 client

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G06F 15/16 470 G06F 15/16 470R 17/30 15/40 330B

Claims (9)

[Claims] 1. A database management system comprising: a plurality of independent servers each having a storage device storing the same database; and one or more clients requesting the server to execute a data processing command for the database. Means for executing a data processing command requested by the client, means for terminating processing according to the data processing command and returning to a state before execution, and processing the result of the data processing command to the client. Means for requesting each of the plurality of servers to execute the same data processing command, and means for determining whether or not the processing results returned from all servers are the same. And at least one of the processing results returned from the plurality of servers is returned from another server. Means for performing a request for terminating the process according to the data processing command and returning to a state before execution and a request for re-executing the data processing command when all of the plurality of servers are different from the processed result. A highly reliable database management system comprising: 2. The client terminates the processing according to the data processing command when there is a server in which the processing result of the requested data processing command is not returned within a predetermined time.
2. The highly reliable database management system according to claim 1, further comprising means for making a request to return to a state before execution and a request to re-execute the data processing command to all of the plurality of servers. . 3. The data processing apparatus according to claim 1, further comprising: means for terminating the processing by the transaction including the data processing instruction when the re-execution of the data processing instruction reaches a predetermined number of times, and returning to a state before the execution. 3. The high reliability database management system according to any one of 2. 4. A data processing execution method for a database management system in which one or more clients request execution of a data processing instruction for the database to a plurality of independent servers each having a storage device storing the same database. A step in which the client requests each of the plurality of servers to execute the same data processing instruction; and a step in which the plurality of servers executes the data processing instruction requested by the client for each database. A step in which the plurality of servers return processing results of the data processing command to the client; anda step in which the client determines whether all of the processing results returned from the plurality of servers are the same. At least one of the processing results returned from multiple servers is from another server When the processing result is different from the transmitted processing result, all of the plurality of servers abort the processing according to the data processing instruction, and after returning to the state before execution, the client requests the plurality of servers to re-execute the data processing instruction. And performing a process for all of the servers. 5. When there is a server for which a processing result of a data processing command requested by the client is not returned within a predetermined time, all of the plurality of servers terminate processing by the data processing command and return to a state before execution. 5. The method according to claim 4, further comprising a step of, after the client, requesting the client to re-execute the data processing command to all of the plurality of servers. 6. The method according to claim 4, further comprising a step of terminating processing by a transaction including the data processing instruction when the re-execution of the data processing instruction has reached a predetermined number of times, and returning to a state before execution. 5. The method for executing processing of a high reliability database according to any one of 5. 7. A database management program wherein a client requests execution of a data processing command to a plurality of independent servers each storing the same database, wherein the client performs the same data processing on each of the plurality of servers. A step of requesting execution of a command, a step of the plurality of servers executing a data processing command requested by the client for each database, and a step of the plurality of servers processing the result of the data processing command to the client. A step of returning, a step of the client determining whether all of the processing results returned from the plurality of servers are the same, and at least one of the processing results returned from the plurality of servers is another server. If the result of the processing is different from the processing result returned from the Aborting the process according to the command and returning to the state before execution, and then performing a request for re-executing the data processing command to all of the plurality of servers. A computer-readable storage medium that stores a database program. 8. When there is a server in which the processing result of the data processing command requested by the client is not returned within a predetermined time, processing by the data processing command for all of the plurality of servers is terminated, and the state before execution is returned. 8. The computer-readable storage according to claim 7, further comprising a step of requesting all of the plurality of servers to re-execute the data processing instruction after the request. Medium. 9. The method according to claim 7, further comprising a step of terminating processing by a transaction including the data processing instruction when the re-execution of the data processing instruction has reached a predetermined number of times, and returning to a state before execution. A computer-readable storage medium storing the high-reliability database program according to any one of claims 8 to 10.