JPH0713840A - Exclusive control method in parallel data access system - Google Patents

Abstract

PURPOSE:To suppress a deadlock to nearly the same degree with processing by a single processor by deciding one access request as a wait or access error when both access requests are in a combination of update and update, or update and reference. CONSTITUTION:Only when data storage areas 1a-1e to be accessed which are specified by access requests from two users overlap with one another at >=2 places as to data in one list format or file format, data to be accessed are locked before an access process request is sent to processors 3a-3e which access the data storage areas 1a-1e. Then one of them is decided as a wait or access error. Consequently, the number of the data areas 1a-1e that two users to >=2 of the data storage areas 1a-1e by the two users is no caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exclusive control method in a parallel data access system such as a database management system which uses a plurality of processors in parallel.

[0002]

2. Description of the Related Art Conventionally, as a database management system using a plurality of processors in parallel, as shown in FIG.
A data access unit 2 that corresponds to a plurality of disk devices provided with data storage areas 1a to 1n and stores and reads data in and from the respective data storage areas 1a to 1n.
A global exclusion control unit 5 that provides a plurality of processors 3a to 3n including a to 2n, connects the processors 3a to 3n with the network 3, and further performs exclusive control for access requests from a plurality of users in the network. Of the access request from the user, the data storage areas 1a to 1n are divided into a plurality of processes if the request can be accessed in parallel, and the processors 1a to 1n corresponding to the disk device to be accessed are analyzed. 1n through the network 4 and also the processors 1a-1n
A processor 8 having a dividing / merging unit 7 for merging and transmitting the access result by the user and a processor 10 having a dictionary management unit 9 for exclusive control are provided. Network 4
There is a system that is connected to the network and reads or writes data from the data storage areas 1a to 1n according to access requests from a plurality of users in the network.

FIG. 9 is a diagram showing a conventional configuration of an exclusive control management table 90 registered in the dictionary management unit 9, which is an exclusive mode used when updating data 1a to 1n in file units or table units. X, a sharing mode S used when referencing in file units or table units, a higher level when updating data in a hierarchical structure such as files and pages in them, records in pages, or rows in tables Intentional exclusion mode IX that intentionally locks a file or table, intentional reference mode IS that intentionally locks a higher-level file or table when referring to the file or table being referred to A shared intentional exclusive mode SIX is provided for use when updating a page or row within.

According to the management table 90, the shared mode S is locked when referring to the data in the data storage areas 1a to 1n, and the exclusive mode X is locked when updating the data. Then, the users who have locked the shared mode S allow the simultaneous execution, and the combination of the shared mode S and the exclusive mode X and the exclusive modes X does not allow the simultaneous execution. This prevents other users from referencing or updating the unauthorized data being updated, or preventing the referenced data from being unduly updated by another user.

Further, in a system for managing access data hierarchically, that is, for managing exclusion of data in two or more layers such as a file, a page in a file and a record in a page, a unit called an upper file. When accessing data with, the shared mode S or exclusive mode X is locked as described above. However, when accessing data in units of lower pages, if it is a reference, it is intended to the upper file first. Sharing mode IS
After locking the page with the shared mode S, if the page is updated, first lock the upper file with the intentional exclusive mode IX and then lock the page with the exclusive mode X.

The combination of the intentional shared mode IS or the intentional exclusive mode IX permits simultaneous execution, and the intentional shared mode IS and the exclusive mode X, and the intentional exclusive mode IX and the shared mode S or the exclusive mode X. Does not allow simultaneous execution. This allows a user to access data in the unit of a file (or table), even if all pages (or rows) in the file (or table) are not locked. Since exclusive control with other users who access in units can be realized, exclusive control between different layers can be efficiently performed.

When updating a part of pages or rows in the file or table currently being referred to, the page or row to be updated is subjected to the intentional exclusion mode IX to perform exclusive control of the area to be updated. .

Here, the file represents the largest unit of data access units, the page in the file represents a part of the unit, and the record in the page represents the smallest unit.

The table shows the largest unit of access to data used in the relational database and corresponds to the above file. Further, the pages in the table show some of the units, the rows in the page show some of the units, and the rows correspond to the above records.

For such an exclusive control method, refer to the DB2 Design & Development Guide (Ju2), page 101 to page 117 of the DB2 Design and Development Guide (June 1988).
ne, 1988) (Gabrielle Wiorkowski, David Kull) pp101-11
7).

FIG. 10 is a flowchart showing the processing of the division / merge unit 7 when exclusive control is performed by the exclusive control management table 90 as shown in FIG. 10, and FIG. 11 is a flowchart showing the processing of the global exclusive control unit 5. Is.
Hereinafter, the conventional exclusive control method will be described with reference to these flowcharts.

It is assumed that the disk devices 1a to 1n store, for example, one tabular table data in a divided manner.

First, when the processing division / merge unit 7 receives an access request from a user through the network 4, it analyzes the access request and uses the network 4 to extract table data from the dictionary management unit 9. Receives information about the storage location (steps S1 and S2),
Divide the access request into multiple processes that can be executed in parallel,
A lock request is issued to the global exclusive control unit 5 using the network 4 (step S3).

For example, when the access request from the user is divided into a reference request for the first page and a reference request for the second page in the table data stored in the data storage area 1a, the first page and the second page. Issue a lock request to lock the respective intentional sharing mode IS for each of the table data of.

In response to this lock request, the global exclusive control unit 5 determines whether or not the table data of the first page and the second page can be accessed according to the management table 90 of FIG. 9 (step S10 of FIG. 11). If access is possible, access is permitted (step S11 in FIG. 11),
The data access unit 2a of the processor 3a, to which the data storage area 1a is connected via the network 4, is controlled to lock the table data of the first page and the second page in the intentional sharing mode IS.

However, if another user is already accessing in the update mode X, the access is not permitted and the access request for the table data of the first page and the second page is completed by the other user. Or waits until the request is made or returns an error to the requesting user (step S12).

When it is accessible, the division / merge unit 7 reads out the table data of the first page and the second page from the data access unit 2a of the processor 3a to which the data storage area 1a is connected. Send the request (step S4).

In response to this read request, the data access unit 2a reads the table data of the first page and the second page and sends it back to the division / merge unit 7 through the network 4.

The dividing / merging unit 7 merges the sent table data of the first page and the second page, and transmits the table data to the user who has made the access request (step S5).

The broken line in FIG. 10 indicates that the case of other exclusive modes is omitted.

[0021]

However, in the above-mentioned conventional exclusive control method, no consideration is given to the case where one data access request is divided and processed in parallel by a plurality of processors. Under such a condition, the probability of waiting occurrence per unit time is high, and the maximum number of waitings that can occur in one request is not "1", but the number of divisions of processing, There is a problem that the probability of lock generation becomes high.

The high probability of deadlock means that when a deadlock occurs, it is necessary to cancel one of the requests and restore the processing performed on the data due to the request. Therefore, it causes a problem that the system performance is degraded.

An object of the present invention is to suppress deadlock, which tends to occur when one data access request is divided and processed in parallel by a plurality of processors, to the same extent as when a single processor is processed. It is to provide an exclusive control method in a parallel data access system that can be performed.

[0024]

In order to achieve the above object, the present invention provides a plurality of storage means for storing data in one table format or a file format in a divided manner, and the storage means according to an access request from a user. In a parallel data access system including a plurality of processors that access data stored in storage means in parallel, access target data specified by access requests from two users regarding one table format or file format data Only when two or more storage areas overlap, lock the data to be accessed before issuing an access processing request to the processor that accesses the data storage area. In the case of the reference combination, one of the access requests is made to wait or an access error. .

[0025]

In general, when there are two or more data storage areas to be locked and the order of locking them is opposite to each other, a deadlock occurs. When multiple data storage areas are accessed in parallel by multiple processors and locked, it is very difficult to match the order of locking those data storage areas among multiple users without losing parallelism. Is.

Therefore, when two or more data storage areas that are accessed in parallel for one table format or file format data overlap each other, the table format or the data storage area before the access processing request is issued to each processor. Lock the data in the file format and set one of them as a wait or access error.

As a result, the number of data storage areas that can be simultaneously accessed by two users is one or less, so that deadlock caused by accessing two or more data storage areas in parallel between two users does not occur. .

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to illustrated embodiments.

FIG. 1 is a schematic block diagram showing an embodiment of the present invention, in which one table 11 of data corresponds to each processor 3a.about.
The data is divided and stored in a plurality of data storage areas 1a to 1e managed by 3e. The detailed configuration of this embodiment is similar to that of FIG. However, the structure of the exclusive control management table of the dictionary management unit 9 is different.

In this embodiment, a plurality of processors 3a-3
In the system in which the access to the table 11 is performed in parallel by the data access units 2a to 2e of e, the exclusive mode is combined only when two or more data storage areas that are accessed in parallel with respect to one table 11 overlap each other. , The global exclusive control unit 5 performs the exclusive control that does not allow simultaneous execution between these users by the process division / merge unit 7.
The feature is that it is performed based on the request from.

That is, "USER4" and "USER"
7 ”, the data storage areas to be accessed overlap at two locations, the data storage areas 1b and 1c. So, if those accesses are updates, or updates and references,
Do not allow simultaneous execution of "USER4" and "USER7".

Similarly, "USER5" and "USER7"
Also, the data storage area to be accessed is the data storage area 1
Since it overlaps at 2 places of c and 1d, simultaneous access is not allowed between updates or in the case of update and reference.

However, in the other two user combinations,
Since the data storage areas to be accessed overlap at one place or less, simultaneous execution is permitted by using the conventional exclusive control.

FIG. 2 shows an example of the data structure stored in the data storage areas 1a to 1e, and the table 11 is divided and stored in a plurality of data storage areas 1a to 1e. This is to improve the performance of parallel processing in the parallel data access system.

The table 11 is composed of a plurality of rows 12, and in order to improve the simultaneous executability of a plurality of users, exclusive control is performed in units of rows 12 smaller than the table 11.

FIG. 3 shows the data structure of the control block in which the global exclusive control unit 5 manages the locked state. In order to manage the current state in which which user has locked which resource. use.

Therefore, the entry 13 of the control block has information such as the user identifier 130, the resource type 131, the resource identifier 132, and the lock mode 133. Further, it has pointers 134 and 135 for easily searching the lock information for each user and the lock information for each resource.

In this embodiment, in particular, the field 1 having the access area instruction information in the lock state management control block
36 is added.

FIG. 4 shows the contents of the exclusive control management table 14 which defines the relationship between the exclusive modes in this embodiment, and FIG. 5 shows the processing flow of the division / merge unit in FIG.
Shows a processing flow of the global exclusive control unit 5. Further, FIG. 7 shows a method of determining whether or not the access area instruction information 136 overlaps at two or more places.

The exclusive control method will be described below with reference to these drawings. However, description of the same parts as the conventional one will be omitted, and only different parts will be described.

First, the exclusive control management table 14 in this embodiment is provided with a conditional exclusive mode CX and a conditional shared mode CS as new exclusive modes.
In the case of accessing two or more data storage areas of No. 1, for the table 11, information 136 indicating the data storage area to be accessed in the table is specified, and the conditional exclusive mode CX (hereinafter, CX) is specified. Mode) or conditional shared mode CS (hereinafter, CS mode) is locked (steps S20 and S21).

Specifically, the five data storage areas 1a to 1
For example, when the data storage areas 1b and 1d are accessed in parallel, before the access processing request is issued to the processors 2b and 2d that access the data storage areas 1b and 1d, the data to be accessed is accessed. CX
Mode or CS mode is locked, and the bit corresponding to the data storage areas 1b and 1d is "010" of "010".
Access area instruction information 1 consisting of a bit string "10"
36 is designated, and this information 136 is transmitted to the global exclusive control unit 5.

Then, the global exclusive control unit 5 has already taken the lock when the newly applied lock is in the CX mode and the already applied lock is in the CX mode or the CS mode, and when the newly applied lock is in the CS mode. When the lock is in the CX mode, the access area instruction information 136 indicating the data storage areas to be accessed is compared,
It is determined whether or not there are two or more overlaps (steps S31 and S32).

As a result, if there are two or more overlaps, a wait or exclusive error is determined and only one access is permitted (step S34).

For example, the access request of "USER4" in FIG. 1 is divided by the dividing / merging unit 7 to be divided into the data storage area 1
It is divided to access b, 1c, and "USER
The access request "5" is divided by the division / merge unit 7 to access the data storage areas 1c, 1d, 1e, and the access request "USER7" is divided / merge unit 7.
The data storage areas 1b, 1c, and 1d are divided by.

Therefore, "USER4" and "USER7"
In and, the data storage area to be accessed overlaps at two locations of the data storage areas 1c and 1d as indicated by the symbol A, and similarly, as shown by the symbol B between “USER5” and “USER7”, The storage areas 1c and 1d overlap at two places.

Therefore, in such a case, simultaneous access is not permitted when the access content is between updates or between update and reference.

However, in the case where there is no overlap in two or more places and there is one place, the processing is performed as in the conventional case (step S3).
3).

In this case, it is determined whether or not the two access area designation information overlaps at two or more places, as shown in FIG. 7, as the logical sum of bit operations of these bit strings (corresponding logical sum of each bit). Can be performed (S61) and it is determined whether or not the number of bits whose value in the bit string of the logical sum is "1" is 2 or more.

To determine the number of bits having a value of "1", the number of bits having a value of "1" is checked by checking whether each value in the bit string is "1". Count. In order to check whether the value of a specific bit is "1", a bit string in which only the value of the bit corresponding to the specific bit is "1" and the values of other bits are "0" is used. It is sufficient to create a logical product of bit operations of the created bit string and the bit string to be examined.

However, in the example of FIG. 7, the bit string to be examined is sequentially shifted to the right by the number of bits for each value from "0" to (n-1) (S62) and the value "1".
The logical product of bit operations with and is obtained (S63), and the results of these logical products are added (S64) to obtain the number S of bits having a value of "1".

Here, n is the number of bits of the entire bit string. It should be noted that a system in which the exclusive control for the table 11 is not performed by the global exclusive control unit 5 but the local exclusive control inside each of the data access units 2a to 2e is an alternative, that is, when the table 11 needs to be locked, In the system in which the data access units 2a to 2e substitute the respective parts of the table divided into the storage areas 1a to 1e for exclusion, the process of step S3 is unnecessary, and the exclusive control of FIG. The management table 14 is CX
Only the mode and CS mode parts are required.

When the processes being executed in parallel leave one process and all the remaining processes are completed, the division / merging unit 7 of the process locks the lock in the CX mode or the CS mode with the IX mode or the IS mode. By changing (or canceling) the mode, concurrency in such cases can be improved.

When the processing division / merging unit 7 uses the network 4 to issue a processing request to each of the data access units 2a to 2e, the data access unit (2a to 2e) on which processor (2a to 2e) is to be processed. It is necessary to manage whether the request has been issued to the server or whether the processing end notification has been received, and it is possible to easily know the processing end status of each data access unit (2a to 2e) from the information.

In the above embodiment, an example in which tabular data is divided and stored has been described, but it goes without saying that file format data can be processed in the same manner.

[0056]

As described above, in the present invention,
An access processing request is issued to the processor accessing the data storage area only when the data storage areas to be accessed specified by the access requests from the two users for one table format or file format data overlap. Before issuing, it locks the data to be accessed, and if both access requests are updates or a combination of updates and references, one access request becomes a wait or an access error, so one data access request It is possible to suppress the deadlock that occurs when multiple processors are processed in parallel by multiple processors to the same level as when they are processed by a single processor, and it is possible to sufficiently improve the performance by parallelizing the processing. There is.

Further, since the simultaneous access is not allowed only for a combination having a particularly high probability of occurrence of deadlock, a simple transaction process and a complicated query or batch process coexist, and the simultaneous execution thereof is supported. In such a parallel data access system, there is also an effect that deadlock can be suppressed without degrading the performance of simple transaction processing.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a data structure of a data storage area.

FIG. 3 is a diagram showing a data structure of a lock state management control block.

FIG. 4 is a configuration diagram of an exclusive control management table according to the embodiment.

FIG. 5 is a flowchart showing a processing flow of a division / merge unit of processing according to the embodiment.

FIG. 6 is a flowchart showing a processing flow of a global exclusive control unit of the embodiment.

FIG. 7 is an explanatory diagram showing a method of determining whether or not access areas overlap at two or more places.

FIG. 8 is a system configuration diagram showing a configuration of a system to which the present invention is applied.

FIG. 9 is a configuration diagram of a conventional exclusive control management table.

FIG. 10 is a flowchart showing a processing flow of a conventional division / merge unit.

FIG. 11 is a flowchart showing a processing flow of a conventional global exclusive control unit.

[Explanation of symbols]

1a to 1n ... Data storage area, 2a to 2n ... Data access unit, 3a to 3n ... Processor, 4 ... Network,
5 ... Global exclusive control unit, 7 ... Process division / merge unit,
14 ... Exclusive control management table.

Claims (1)

[Claims] 1. A plurality of storage means for storing one tabular or file format data in a divided manner and a plurality of storage means for accessing data stored in the storage means in parallel in response to an access request from a user. An exclusive control method for access requests in a parallel data access system including a processor, wherein two or more data storage areas to be accessed specified by access requests from two users with respect to one table format or file format data are provided. Only when overlapping, lock the data to be accessed before issuing an access processing request to the processor that accesses the data storage area, and if both access requests are updates or a combination of updates and references, Parallel data, characterized by waiting for one access request or an access error Exclusive control method for data access system.