JPH0516058B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a database prefetch control device in an information processing device.

Preemption control is the process that will be processed in the near future.
Or, if there is any data that could lead to that possibility,
This is to transfer data from the secondary storage device to the main memory. Due to this preemption control, the apparent I/
O time is shortened, and job processing time can be shortened.

However, most database systems do not perform this preemption control. Prefetching control is usually expressed by software, and in order to detect data pages that are candidates for prefetching, processing unrelated to the original work is performed.
This is because the CPU overhead increases.

An object of the present invention, in order to eliminate the above-mentioned drawbacks, is to provide a processor exclusively for preemption control independent of the main processor and perform parallel processing, thereby reducing central processing unit overhead for processing unrelated to the original work. The object of the present invention is to realize a proactive control device that prevents the problem from occurring and is inexpensive.

Further, the preemption control device of the present invention is intended for a database record management system, and is different from a record management system for a general-purpose computer. For general-purpose computer systems, data and programs (code)
It is very difficult to predict the operating characteristics of memory management because it targets a mixture of , it attempts to save as much of what was previously accessed in main memory as possible in main memory and reuse it.

On the other hand, in the database system targeted by the present invention, only data is processed;
Since it is structured data with an index file, access characteristics can be easily predicted according to the structure of the index. Therefore, by making full use of its characteristics, we proactively perform proactive staging to reduce apparent I/O
This is an attempt to shorten the time.

According to the present invention, in a computer system that accesses a database via an index, there is provided an index record reference section that refers to an entry of an index record on a main storage device, and a page number storage section that stores a data page number existing on the main memory. and a prefetch page determination unit that checks the consistency between the page number of the database record indicated in the index record obtained by the towing record reference unit and the contents of the page number recording unit, and determines the address of the next index record. It consists of an address adder and a prefetch control unit that performs control for detecting prefetch candidates, and when a record search command is requested from a program, the index record address corresponding to the newly switched current record is used as the base point. In order to detect the data page number of the next record that does not exist on the recording device, it receives a data page prefetch candidate detection instruction from the central processing unit and performs parallel processing with the central processing unit to detect the index page that exists on the main recording device. The content of the index record is sequentially examined using the specified address of the index record as a base point, and the page number containing the data record included in the index record detects the first retrieved record whose page number does not match the content of the page number storage unit; A database prefetch control device is obtained, characterized in that the page number is returned to the central processing unit as a data page of a prefetch candidate.

The database prefetch control device of the present invention is intended for a database system that accesses a database via an index.

An index is created corresponding to a specific field (key field) of a record, and is a table that has pairs of field values and corresponding record addresses. This table is typically organized in ascending order according to field values. Each entry in the table (pair of field value and record address) will be referred to herein as a traction record.

By using this index, a conditional search (content search) regarding the value of a key field can be executed easily and quickly. That is, it can be easily predicted that in this unusual database system, there are many processes in which records are sequentially accessed according to an index.

The present invention uses this index to detect data page prefetch candidates.

FIG. 1 is a block diagram showing the positioning of the database prefetch control device of the present invention. As shown in the figure, the database prefetch control device 3 is connected to the central processing unit 1 and main storage device 2 of the computer.

The database prefetch control device 3 receives from the central processing unit 1 the address of the index page existing on the main storage device 2 and the in-page index record number. Then, using that address as a base, the index pages on the main storage device 2 are sequentially operated, the data page number indicated in the index record is checked, and it is checked whether the target data page exists on the main storage device 2, Detects the first index record number with a data page number that does not exist in main memory. and,
The data page number is returned to the central processing unit 1.
The central processing unit 1 regards the data page number as a candidate for pre-fetching and gives a data page pre-fetching instruction to the I/O processing unit 4.

An embodiment of the present invention will be described below with reference to FIG. FIG. 2 is a block diagram showing an example of the configuration of the database prefetch control device of the present invention. In the figure, a portion 3 surrounded by a broken line is a database prefetch control device. 1 indicates a central processing unit, and 2 indicates a main storage device.

The database prefetch control device 3 includes a prefetch control unit 5, a traction record reference unit 6 that extracts a page number of a prefetch candidate, an address adder 7, and a prefetch controller that determines whether a page number indicated in an index record can be a true prefetch page. A page determination unit 8, a page number storage unit 9 that stores the data page number on the main memory, a register 10 that indicates the address of the index record, and a register 11 that indicates the page number of the prefetch candidate.
Consists of. Reference numerals 15 to 31 indicate connection buses for each of the aforementioned processing mechanisms.

This operation will be explained next. In order to issue a request to the database prefetch control device 3 to determine the page to be prefetched, the central processing unit 1 sets the address of the index record, which will be the base point for searching for a prefetch candidate, in the index record address register 10 via the connection bus 17. do. Then, a preemption candidate detection signal is sent to the preemption control section 5 via the connection bus 16. The address of the index record is indicated by the leading address (IBP) of the index page existing on the main storage device 2 and the index record number within the index page (ILN).

Note that the pre-fetch page determination request is made in response to a record search command requested by the program, triggered by switching to a new record to be processed (referred to as the current record).

Also, using the address of the index record corresponding to the newly switched current record as a base point, the data page number of the next record that does not exist on the main memory is detected.

The prefetch control unit 5 passes control to the index record reference unit 6 via the connection bus 29. The index record reference section 6 uses the address register 10 as an input to calculate an address indicating the position of the data page number indicated in the index record. For ease of explanation, index records are fixed length of length ISZ, and of length
It is assumed to consist of a KSZ key field and a database record address. It is assumed that the database record address is composed of a page number PNO and an in-page record number LNO. The main memory data address RAD for obtaining the data page number (PNO) containing the above database record is given by the following formula.

When RAD=IBP+ISZ(ILN-1)+KSZRAD is determined,
Issue a request to retrieve data in the index page. The data (prefetch candidate page number) accessed from the main memory is set in the register 11.

Next, control is passed to the prefetch page determination unit 8 via the connection bus 30. The prefetch determination unit 8 checks whether or not all of the page numbers stored in the page number storage unit 9 match the values in the reference register 11. The page number storage unit 9 stores the page numbers of all data pages currently existing in the buffer pool on the main storage device 2. That is, if there is a page number that matches the value of register 11, it is confirmed that the database record (including the page) indicated in the index record exists on the buffer of main storage device 2, and it is selected from the data page prefetch candidates. It comes off. and,
Control is passed to address adder 7 to read the next index record. When it is confirmed that there is no value matching the value of register 11, connection bus 20
The prefetch control unit 5 is notified of the detection of the candidate page number. The preemption control unit 5 passes control to the central processing unit 1 via the connection bus 15. The central processing unit 1 receives the page number of the prefetch candidate via the connection bus 31 .

The address adder 7 controlled by the connection bus 21 increments the index record number (ILN) in the index page of the index record address in the register 10 by 1 in order to detect a prefetch candidate using the next index record as a clue. . If the value of ILN exceeds the number of index records within a page, the prefetch control unit 5 is notified via the connection bus 19 that no data page number to be prefetched is detected in the specified index page. If the number of index records within a page does not exceed the number, control is passed to the index record reference unit 6 via the bus line 24. The same process is repeated thereafter.

In addition, the data page in the buffer pool on main storage device 2 is replaced (replacement).
If this occurs, the central processing unit 1 sends the page number (old page number and new page number) to be replaced to the page number storage section 9 via the connection bus 18.

The page number storage unit 9 similarly performs page number replacement processing.

By providing the database prefetch control device as described above, the following effects can be brought about. First, compared to conventional database systems that employ preemption control, the processing load for preemption control that is not related to the original work can be removed from the central processing unit. Second, by operating the central processing unit and the preemption control device in parallel, it is possible to sufficiently reduce the apparent I/O time due to the preemption effect. That is,
In conventional systems, the processing of the central processing unit to perform preemption control increases, so the effect is calculated by subtracting the CPU processing time for preemption control from the apparent I/O time reduction that can be considered purely. Become something. In the present invention, the processing time of the central processing unit for preemption control is reduced by parallel operation.
It can be considered as

According to the present invention, it is possible to prevent the overhead of the central processing unit for processing unrelated to the original work, and to realize a preemptive control device at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the positioning of the present invention;
FIG. 2 is a block diagram of an embodiment of the database prefetch control device of the present invention. In the figure, 1...Central processing unit, 2...Main storage device, 3...Database prefetch control device, 4...
... I/O processing device, 5 ... Preemption control unit, 6 ...
...index record reference section, 7...address adder,
8... Prefetch page determination section, 9... Page number storage section, 10... Address register, 11... Data register.

Claims (1)

[Claims] 1. In a computer system that accesses a database via an index, a reference record reference section that references an entry of an index record on a main memory, a page number recording section that stores a data page number existing on the main memory, and the above-mentioned a pre-fetch page determination unit that checks the consistency between the page number of the database record indicated in the index record obtained from the index record reference unit and the content of the page number recording unit; and an address adder that determines the address of the next index record. and a prefetch control unit that performs control for detecting prefetch candidates.When a record search command is requested from a program, data is stored in the main memory based on the address of the index record corresponding to the newly switched current record. In order to detect the data page number of the next record that does not exist in the main memory, it receives an instruction from the central processing unit to detect a data page preemption candidate and performs parallel processing with the central processing unit. Using the address of the index record as a base point, the contents of the index record are sequentially examined, the first index record whose page number including the data record contained in the index record does not match the contents of the page number storage section, and the page number A database prefetch control device characterized in that the data page is returned to a central processing unit as a data page of a prefetch candidate.