JPH01277943A - Recovery system for dead lock - Google Patents

Abstract

PURPOSE:To perform the recovery processing even at the time of the occurrence of dead lock by saving contents of the data part of a user program and file currency in a save medium by a check point settling means and discriminating whether dead lock occurs or not at the time of issue of a data operation instruction from the program. CONSTITUTION:When a check point settling instruction 9 is issued from a user program 1, a check point settling means 3 in a data base monitor 2 is operated to reflect update log information stored in an external journal file 6 on a data base file 5. The return address for the occurrence of dead lock (the instruction address next to the settling instruction 9), the size of a data part 7 of the program 1, and file currency of all data bases of the program 1 are stored in the first record of the file 6 as roll back information, and contents of the data part 7 are divided and are used as another roll back information and are stored in the second record of the file, and hereafter, the similar processing is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a deadlock recovery method for performing recovery processing when a deadlock occurs in a checkpoint-based indirect update type database system.

[Conventional technology]

Conventionally, the update history information of update-related database operation commands for the database is stored in a temporary storage file such as a journal file, and the contents of the temporary storage file are reflected in the database file at checkpoint-1, an indirect update type using the checkpoint method. In database systems, in order to deal with deadlocks, when establishing a checkpoint, the contents of the data section of the user program and all file currencies held by the user program (information indicating which record in the file the user program is trying to refer to) are checked. The process of saving data, the process of determining whether a deadlock has occurred when executing an update-related database operation command, and the process of saving the contents of the data section and file currency that were saved above when a deadlock occurs to the user program. A process for restoring the state of the user program to the state when the latest checkpoint was established, and a process for causing re-execution from the latest checkpoint are embedded in the user program.

[Problem to be solved by the invention]

Conventionally, as described above, it is necessary to embed various processes for performing the recovery process into the user program, which increases the amount of coding in the user program, placing a burden on the user and easily causing bugs.

An object of the present invention is to provide a deadlock recovery method that can perform recovery processing when a deadlock occurs without imposing a burden on the user.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a checkpoint-based indirect update type database system, in which the user program updates the user program in response to issuance of a checkpoint establishment command from the user program. A checkpoint indicator means for saving information regarding the contents of the data section, file currency, and the address of the checkpoint establishment instruction to a saving medium, and executing the instruction in response to the issuance of a database operation instruction from the user program. At the same time, it is determined whether or not a deadlock has occurred, and by determining that a deadlock has occurred, the contents of the data section saved in the save medium and the file currency are returned to the user program, and the file currency is returned to the user program. A database access means is provided for transferring control to the next instruction of the checkpoint establishment instruction issued just before based on information regarding the address of the checkpoint establishment instruction.

[For production]

When a checkpoint establishment command is issued from the user program, the checkpoint establishment means saves the contents of the data section of the user program and the file currency to the save medium, and also saves information regarding the address of the issued checkpoint establishment command. Save to evacuation medium. When a database operation command is issued from a user program, the database access means processes the command and determines whether a deadlock has occurred.
By determining that a deadlock has occurred, the contents of the data section saved on the save medium and the file currency are returned to the user program, returning the user program to the state it was in when the previous checkpoint establishment instruction was executed, and then the save Control is transferred to the next instruction of the immediately preceding checkpoint establishment instruction in accordance with information regarding the address of the checkpoint establishment instruction saved in the medium.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, in which a user program 1, a database monitor 2, a database file 5 that actually stores database data,
It includes a journal file 6 that stores update history information of update-related database operation commands for the database. The user program 1 is composed of a data section 7 and an instruction section 8, and the instruction section 8 has a checkpoint establishment instruction 9 and a database operation instruction 10 embedded therein. The database monitor 2 is a part of the operating system and manages the overall operation of the database, and includes checkpoint establishment means 3 for processing checkpoint establishment commands and database access means 4 for processing database operation commands. Contains.

Next, the operation of this embodiment will be explained.

The checkpoint establishment means 3 issues a checkpoint command 9 from the user program 1, reflects the update history information stored in the journal file 6 in the database file 5, and then returns the return address when a deadlock occurs. (Address of the next instruction after checkpoint establishment instruction 9).

The size of the data section 7 of the user program 1 and the file currency of all databases held by the user program 1 are stored as roll bank information A in the record format shown in FIG. Furthermore, the contents of the data section 7 are divided into predetermined sizes, and each part is stored as rollback information B in order from the second record of the journal file 6 in the record format shown in FIG. In addition, in Figure 2+al,
The record identification section 21 stores information indicating that the record is for rollback information A, and the return address section 22 stores checkpoint establishment command 9.
The address of the next instruction is stored in the size field 23 in the data field 7.
Information f1 indicating the size of is stored in the file currency section 24-1.
~24-n store file currencies of files F1 to Fn (not shown) stored in the database file 5, respectively, and record identification section 31 stores the file currency of files F1 to Fn (not shown) stored in the database file 5. Information indicating that the record is for back information B is stored, and the contents of the data section 7 are stored in the memory image section 32.

When the database access means 4 receives the database operation command 10 from the user program 1, it performs the following process shown in the flowchart of FIG.

The database access means 4, in box Bl,
First, the original processing of the database operation command 100, that is, the processing of accessing the database file 5, is performed.
At this time, if the database operation instruction 10 is an update-related instruction, the database access means 4 writes update history information in the journal file 6 in the record format shown in FIG. 2 (C1) in box B1. This update history information writing process is performed every time a database operation command is issued, and the update history corresponding to the update-based database operation command IO executed first after the checkpoint establishment command 9 is executed. The information is written to the record next to rollback information B, and update history information is written in order every time an update-related database operation command is issued. The section 41 stores information indicating that the record is a record regarding update history information, and the information section 42 stores update history information.

Next, the database access means 4 selects the next box B2.
Checks whether the database system is in a deadlock state or not, and if it is determined that it is not in a deadlock state, returns control to the instruction following database access instruction 10. Box B3) If so, the processes in boxes 84 to B8 are performed. In box B4, the database access means 4 performs the process of positioning the journal file 6 at the 1st code, that is, the process of setting the processing start record of the journal file 6 at the 1st code, Box B5 replaces the contents of each file currency in user program 1 with the contents of file currency sections 24-1 to 24-n stored in the 1st code of journal file 6, and box B6 replaces the contents of each file currency in user program 1 The contents of the data section 7 are replaced with the contents of the memory image section 32 stored after the second record of the journal file 6. As a result, the state of the user program 1 is returned to the state at the time the checkpoint establishment instruction 9 was issued. In this way, when the state of the user program 1 is returned to the state at the time of issuing the checkpoint establishment instruction 9, the database access means 4 returns to the box B.
In step 7, the update history information stored in the journal file 6 is deleted, and in the next box B8, control is transferred to the command at the address stored in the return address section 22 of the journal file 6. As a result, the process is re-executed from the instruction following the checkpoint establishment instruction 9.

〔Effect of the invention〕

As described above, the present invention enables a user to -
a checkpoint establishment means for saving information regarding the contents of the data section of the program, the file currency, and the address of the checkpoint establishment instruction to a save medium; and determining whether a deadlock has occurred during execution of the database operation instruction; By determining that a deadlock has occurred, the information stored in the evacuation medium is returned to the user program to return the state of the user program to the state at the time the checkpoint establishment command was issued, and then the checkpoint stored in the evacuation medium is restored. This system is equipped with a database access means that transfers control to the next instruction after the checkpoint establishment instruction according to the information regarding the address of the point establishment instruction. Since there is no need to code the process of saving the information or the process of restoring the saved information, there is an effect that the def-lock recovery process can be performed reliably without putting a burden on the user.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a diagram showing the record format of the journal file 6, and FIG. 3 is a flowchart showing an example of processing by the database access means 4. In the figure, 1...user program, 2...database monitor, 3...checkpoint establishment means,
4...Database access means, 5...Data header file, 6...Journal file, 7...
Data section, 8... Instruction section, 9... Checkpoint establishment instruction, 10... Database operation instruction.

Claims (1)

[Claims] In a checkpoint-based indirect update type database system, in response to issuance of a checkpoint establishment command from a user program, the contents of the data section of the user program, the file currency, and the checkpoint establishment a checkpoint establishing means for saving information regarding the address of the instruction to a saving medium; responsive to the issuance of a database operation instruction from a user program, executing the instruction and determining whether a deadlock has occurred; By determining that a deadlock has occurred, the contents of the data section saved in the save medium and the file currency are returned to the user program, and the checkpoint establishment command issued just before is returned to the user program based on the information regarding the address of the checkpoint establishment instruction. and database access means for transferring control to an instruction following the checkpoint establishment instruction.