JP2002099465A - Cache control method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve the response time and throughput of a database system by efficiently using a hierarchical cache area. In a computer system having a hierarchical cache area, according to data access characteristics,
The cache area to be used is determined for each file.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a cache area prepared for realizing high-speed access to frequently accessed data on a computer system holding a large amount of data.

[0002]

2. Description of the Related Art The amount of data and the amount of processing handled by a backbone computer system and the like are increasing year by year.

In general, in a database system, in order to improve response performance and throughput, a work area is secured on a computer node and frequently accessed data is arranged in the area (hereinafter, referred to as caching). In order to reduce the number of accesses to the external storage device in which data is stored.

As one example, Japanese Patent Application Laid-Open No. H11-110
No. 270 can be mentioned. JP-A-11-11
In No. 0270, use the cache memory effectively,
Disclosed is a file management system and a file management method that can handle a large number of files.

[0005] Further, on an external storage device, Japanese Patent Laid-Open No.
000-172449 and JP-A-2000-181.
Data caching is performed using a semiconductor memory device called a disk cache device as disclosed in Japanese Patent Publication No. 798 to shorten the access time.

While measures have been devised to improve processing performance by reducing the input / output time, there has also emerged an embodiment in which data retrieval processing is performed in parallel using a plurality of computer nodes.

In such an embodiment, in order to speed up access to data shared between computer nodes, as described in Japanese Patent Laid-Open Publication No. Hei 5-88966, it is extended as a shared device between computer nodes. A method of caching data shared between computer nodes using a storage device is disclosed.

[0008]

However, in the case where one computer node uses a plurality of caches, the same data is redundantly staged in a plurality of cache areas, and the use efficiency of the cache area is reduced. There is a problem to make it.

For example, in a system provided with a cache arranged on a real storage device (hereinafter referred to as a memory cache) and a cache prepared by a disk device (hereinafter referred to as a disk cache), in particular, refer to Data that is frequently updated is more likely to be placed in each of the memory cache and the disk cache, which causes a decrease in the use efficiency of the cache area.

[0010] In such a case, re-referencing is high,
In addition, it is more efficient to arrange data in which the reference frequency is higher than the update frequency in the memory cache, and to arrange the data in which the above-mentioned reference update is frequently repeated, in the disk cache.

Further, in the case of performing data search processing in parallel using a plurality of computer nodes, the following problem arises in the use of the caching area.

First, a cache (hereinafter referred to as a memory cache) arranged on a real storage device is arranged on each computer node. Therefore, the same data
It may be located in multiple memory caches. Therefore, when data is updated on a certain computer node,
In order to guarantee data consistency, the computer node must perform a process of notifying other computer nodes of the update. If the updated data is stored in the memory cache of another computer node that has received the notification, a procedure for invalidating the data must be taken.

Therefore, as the number of computer nodes increases,
It is necessary when data update as described above occurs,
There is a problem that the overhead of the data update notification process and the data invalidation process increases.

On the other hand, in the case of a disk cache, it is prepared corresponding to an external storage device in which original data is stored. Therefore, data is not allocated to a plurality of caches. Therefore, there is no processing that must be executed in conjunction with updating of data.

However, there is a problem that the disk cache requires more processing time than the memory cache.
For example, for the input request of the database system,
After the operating system performs a procedural process for executing the actual input operation, the actual input operation is started,
If the target data exists in the disk cache during the process, a cache hit occurs for the first time,
You will be able to access it.

As described above, the memory cache and the disk cache have advantages and disadvantages. In addition, in a case where database processing is performed by combining a plurality of caches such as a memory cache and a disk cache, and a cache provided in an extended storage device, each cache independently controls data to be arranged on the cache. In such a case, there is a possibility that the same data is redundantly stored in a plurality of caches. Therefore, there is also a problem that the use efficiency of the cache is greatly reduced.

An object of the present invention is to improve the response time and the throughput of the database system by efficiently using the above-described hierarchical cache area.

[0018]

In order to solve the above problems, one computer node has two or more hierarchized cache areas, and stores data accessed by a program operating on the computer node. In the cache control method for allocating to each of the cache areas, the ratio between the step of registering the file identifier to which the data to be allocated to each of the cache areas belongs and the update processing of the reference processing of the file using each of the cache areas is set to the target value And a step of monitoring the number of reference requests and update requests for the data of the file arranged in each cache area for each file in the file unit. The ratio between the number of reference requests and the number of update requests is
Using an area storing data belonging to a file that does not satisfy the target value as an area for caching data other than the file.

In a computer system constituted by a plurality of computer nodes, the problem is solved by providing similar steps.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a configuration diagram showing the first embodiment.

Reference numeral 100 denotes a computer, and a central processing unit (C)
PU) 200 and a main storage device (MS) 300.

On the MS 100, a user program 40
0, MS cache monitor processing 500, MS cache monitor management table 600, MS cache processing 1
300 and an MS cache.

A disk controller 1700 for controlling the driving of the external storage device is connected to the computer 100,
The disk control device 1700 controls the operation of the disk 1800. The disk control device 1700 is provided with a disk cache 1750, which caches data every time an input / output operation of data is performed, thereby shortening the response time at the time of re-reference. The data arranged in the disk cache 1750 is stored in a FIFO (Fi
rst In First Out) or LRU
(Least Recently Used), and performs data staging and destaging.

The disk 1800 stores a file A1 accessed by the user program group 400 during operation.
Many files such as 810 and file B1820 are arranged.

When the user program group 400 issues an input / output request (GET / PUT) during operation, control passes to the MS cache processing 1300. MS cache processing 1
As disclosed in Japanese Patent Application Laid-Open No. H11-110270, an MS cache is prepared on the MS 300 and data is cached to reduce actual input / output operations. In the embodiment of the present invention, resident in the cache and release of resident can be performed in file units.

Each time an input / output request is received from the user program 400, the MS cache processing 1300 is executed.
Calls the monitoring process 500 for the MS cache. M
The S cache monitoring process 500 monitors the access status of the file from the user program 400, determines whether or not a predetermined criterion is satisfied, and staging of the data to the MS cache 1400 in file units. And destaging to the MS cache processing 1300. The MS cache process that has received the instruction performs staging and destaging to the MS cache in file units according to the instruction.

FIG. 2 is a configuration diagram of the monitor management table 600 for MS cache. The MS cache monitor management table 600 stores the name of the file whose data is to be cached in the MS cache 1400, the access status of each file, and the conditions for caching the data of each file.

Here, the name of the file for caching data and the conditions for caching data are defined in advance in system parameters of the computer system. When the system is started, an area for the MS cache monitor management table 600 is secured, and the file name defined in the system parameter and the caching condition are registered.

Next, the structure 600 of the monitor management table for MS cache will be described.

In the structure 600 of the monitor management table for MS cache, a valid flag 610, a file name 620, a reference count 630, an update count 640, and a threshold 650 are registered for each file whose data is to be cached on the MS cache 1400. Have been.

When the valid flag 610 is ON, it indicates that the data of the corresponding file can be arranged in the MS cache 1400. When the valid flag 620 is OFF, the data of the corresponding file is M
This indicates that it cannot be placed on the S cache 1400. It should be noted that all of the valid flags 610 are turned on when the system is started.

A field 620 stores a file name. 620 stores a file name of a candidate using the MS cache 1400. The fields for storing the access status of each file are 630 and 64.
0. 630 stores the total number of reference requests, and 640 stores the total number of update requests. Then, in 650, the corresponding file is MS
A condition (threshold) that can use the cache 1400 is stored. In the embodiment of the present invention, the reference ratio is stored. The reference rate can be obtained by reference frequency / (reference frequency + update frequency). When determining whether to perform caching, the number of references 630 and the number of references 64 are determined.
The reference rate is calculated from 0, and if it is larger than the corresponding threshold value, caching is performed, and if it is smaller, caching is stopped.

Using the MS cache monitor management table 600, how the MS cache monitor process 500 operates will be described with reference to FIG.

The MS cache monitor process 500 is called from the MS cache process 1300 each time the MS cache process 1300 that receives an input / output request from the user program 400 operates.

First, at 505, the file requested to be accessed is stored in the monitor management table 600 for MS cache.
Is searched using the file name 620 as a key. If it is registered, the process proceeds to 510, and if it is not registered, the process proceeds to 550 to end the process and return to the caller.

At 510, it is determined whether or not monitoring for determining whether to cache the file is performed. In this determination, the reference count 630 and the update count 6
Judgment is made based on whether or not the sum of 40 is a multiple of 10,000. If it is a multiple, go to 515; if not, go to 525.

At 515, it is determined whether or not the target file satisfies the conditions for caching. This determination is made based on the reference level as described above. If the reference degree is larger than the threshold value 650, it is determined that the condition for caching is satisfied, and the process proceeds to 520. on the other hand,
If the reference degree is smaller than the threshold value 650, it is determined that the condition for caching is not satisfied, and 530
Proceed to.

At 520, it is determined whether or not the valid flag 610 is ON. 5 when the valid flag is ON
Proceed at 25 and proceed to 535 if it is OFF.

At 525, the file access request is
If it is a reference, the number of references 630 is counted up, and if it is an update request, the number of updates 650 is counted up, the process proceeds to 550, and returns to the caller.

On the other hand, if it is determined in 515 that the conditions for caching are not satisfied, 53
At 0, the destaging process is performed. In the destaging process, the valid flag 610 corresponding to the file requested to be accessed is turned off, and the MS cache process 130
0 requests that the area that caches the data of the file be placed in an unused state. With this request, the region that has been attracted is used for caching data of another file. After completing this procedure, go to 525.

Further, at 520, the valid flag 610 is set to O
The case where it is determined to be FF will be described. This case indicates that the condition for caching the file is satisfied, but the data is not cached because the valid flag is OFF. So first. At 535, the reference count 630 and the update count 640 are cleared to zero to prepare for the next and subsequent monitoring. And
At 540, the valid flag is turned on to instruct the start of caching, and the process proceeds to 525.

Next, a second embodiment will be described with reference to FIGS.

In the second embodiment, a cache is provided in each of the main storage device, the extended storage device, and the disk control device.

The configuration of the system will be described with reference to FIG.

In this case, MS cache 1 of MS 300
400 is the first tier cache and ES1600
ES cache 1650 of the second hierarchy,
Disk cache 185 of the disk controller 1800
0 is the cache of the third hierarchy.

Hereinafter, differences from the first embodiment shown in FIG. 1 will be described.

An MS / ES cache process 1500 is prepared instead of the MS cache process 1300 in FIG. When the MS / ES cache processing 1500 receives a file input request from the user program 400,
It searches whether the corresponding data is stored in the S cache 1400, and if not, searches the ES cache 1650. When the corresponding data is stored in the MS cache 1400 or the ES cache 1650, the data is passed to the user program,
Reduce actual input operations. MS Cache 1400 and ES
If the corresponding data does not exist in both of the caches 1650, a real input command is issued and the disk 180 is deleted.
Input from 0.

On the other hand, when there is a data output request from the user program 400, first, the data is placed on the MS cache, and if the data is described in the MS cache monitor management table 600, the data is transferred to the MS cache. After placing the data on the disk 1400,
Output to 0. Monitor management table 6 for MS cache
Monitor management table for ES cache 10 instead of 00
00, the ES cache 1650
After that, the data is output to the disk 1800.

The MS / ES cache processing 1500
Each time the S cache 1400 is manipulated or searched for data, the MS cache monitor process 7
Call 00. Then, each time a data operation or data search is performed on the ES cache 1650, the ES cache monitor process 900 is called.

As in the first embodiment, the MS cache monitor process 700 dynamically controls data to be allocated to the MS cache 1400, and dynamically controls data to be allocated to the ES cache 1650. But
This is the ES cache monitor process 900. Then, a management table is prepared for each. The MS cache monitor process 700 uses the MS cache monitor management table 800, and the ES cache monitor process 9
00 is the ES cache monitor management table 1000
Use

Monitor management table 80 for MS cache
0 and the structure of the ES cache monitor management table 1000 are the same. This is the same as the MS cache monitor management table 600 described in the first embodiment.

When the system is started, these two tables are generated and the same file name is registered. However, the threshold is different between the MS cache 1400 and the ES cache 1650. Further, the valid flag for the same file is stored in the monitor management table 800 for the MS cache and the monitor management table 1000 for the ES cache.
Only one of them is turned ON. That is, in both the MS cache 1400 and the ES cache 1650,
No data in the same file is cached.

Next, the flow of the MS cache monitor process 700 will be described with reference to FIG.

First, in step 705, a search is performed using the file name as a key to determine whether the file requested to be accessed is registered in the monitor management table for MS cache. If it has been registered, the process proceeds to 710; if it has not been registered, the process proceeds to 750 to end the process and return to the caller.

At 710, it is determined whether or not monitoring for determining whether to cache the file is performed. In this determination, it is determined whether or not the sum of the reference count and the update count is a multiple of 10,000. If it is a multiple, go to 715; otherwise, go to 730.

At 715, as in the first embodiment, it is determined whether or not the target file satisfies the condition for sleeping. If satisfied, proceed to 720; if not, proceed to 730. At 720, it is checked whether or not the valid flag of the access target file in the MS cache monitor management table 800 is ON. ON
If yes, go to 725; if off, 740
Proceed to. In step 725, if the access request is a reference request, the number of references corresponding to the corresponding file name in the MS cache monitor management table 800 is updated. The update count corresponding to the file name to be updated is updated.

If it is determined at 715 that the caching condition is not satisfied, then at 730 the MS cache 1400
Destaging from. Specifically, the validity flag corresponding to the corresponding file name in the MS cache monitor management table 800 is turned off. And MS
For the / ES cache processing 1300, the MS cache 140 caching the data of the file
Requests that the area in 0 be unused. Then, at 735, a staging operation to the ES cache is performed. Specifically, the valid flag corresponding to the file in the ES cache monitor management table 1000 is set to O.
Set N and proceed to 725.

If it is determined in 720 that the valid flag corresponding to the file in the MS cache monitor management table 800 is OFF, the process proceeds to 740.
Then, the field of the number of references and the field of the number of updates corresponding to the file in the MS cache monitor management table 800 are cleared to zero.

Then, at 745, a staging operation to the MS cache is performed. Specifically, when the valid flag corresponding to the file in the ES cache monitor management table 1000 is ON, the valid flag is turned OFF, and M
For the S / ES cache processing 1300, the ES cache 16 caching the data of the file
Request that the area in 50 be unused. Then, the validity flag of the corresponding file in the MS cache monitor management table 800 is turned ON, and the process proceeds to 725.

Next, the flow of the ES cache monitor process 900 will be described with reference to FIG.

First, in step 705, a search is performed using the file name as a key to determine whether the file requested to be accessed is registered in the monitor management table for MS cache. If it has been registered, the process proceeds to 710; if it has not been registered, the process proceeds to 750 to end the process and return to the caller.

At 710, it is determined whether or not monitoring for determining whether to cache the file is performed. In this determination, it is determined whether or not the sum of the reference count and the update count is a multiple of 10,000. If it is a multiple, go to 715; otherwise, go to 730.

At 715, it is determined whether or not the target file satisfies the caching condition as in the first embodiment. If satisfied, proceed to 720; if not, proceed to 730. At 720, it is checked whether or not the valid flag of the access target file in the MS cache monitor management table 800 is ON.
If it is ON, proceed to 725; if it is OFF, 7
Proceed to 40. At 725, if the access request is a reference request, the MS cache monitor management table 800
In the case of an update request, the update count corresponding to the corresponding file name in the MS cache monitor management table 800 is updated.

If it is determined at 715 that the caching condition is not satisfied, then at 730 the MS cache 14
Destaging from 00. Specifically, the validity flag corresponding to the corresponding file name in the MS cache monitor management table 800 is turned off. And
For the MS / ES cache processing 1300, the MS cache 1 caching the data of the file
Request that the area in 400 be unused.
Then, at 735, a staging operation to the ES cache is performed. More specifically, the validity flag corresponding to the file in the ES cache monitor management table 1000 is turned ON, and the process proceeds to 725.

If it is determined in 720 that the valid flag corresponding to the file in the MS cache monitor management table 800 is OFF, the process proceeds to 740.
Then, the field of the number of references and the field of the number of updates corresponding to the file in the MS cache monitor management table 800 are cleared to zero.

Then, at 745, a staging operation to the MS cache is performed. Specifically, when the valid flag corresponding to the file in the ES cache monitor management table 1000 is ON, the valid flag is turned OFF, and M
For the S / ES cache processing 1300, the ES cache 16 caching the data of the file
Request that the area in 50 be unused. Then, the validity flag of the corresponding file in the MS cache monitor management table 800 is turned ON, and the process proceeds to 725.

Next, the flow of the ES cache monitor process 900 will be described with reference to FIG.

First, at 905, the file requested to be accessed is stored in the ES cache monitor management table 100.
0 is searched using the file name as a key. If registered, the process proceeds to 910; if not registered, the process proceeds to 950 to end the process and return to the caller.

At 910, it is determined whether or not monitoring for determining whether to cache the file is performed. In this determination, it is determined whether or not the sum of the reference count and the update count is a multiple of 10,000. If it is a multiple, go to 915; if not, go to 930.

At 915, it is determined whether or not the target file satisfies the caching condition as in the first embodiment. If satisfied, proceed to 920; otherwise, proceed to 930. At 920, it is checked whether or not the valid flag of the access target file in the ES cache monitor management table 1000 is ON. If it is ON, proceed to 925; if it is OFF, proceed to 935. At 925, if the access request is a reference request, the ES cache monitor management table 1
000, the update count corresponding to the corresponding file name in the ES cache monitor management table 1000 is updated.

If it is determined at 915 that the caching condition is not satisfied, the ES cache 16 is determined at 930.
Destaging from 50. Specifically, the validity flag corresponding to the corresponding file name in the ES cache monitor management table 1000 is turned off. Then, it requests the MS / ES cache processing 1300 to make the area in the ES cache 1650 that caches the data of the file into an unused state, and proceeds to 725.

If it is determined in 920 that the valid flag corresponding to the file in the monitor management table for MS cache 1000 is OFF, 935 is set.
Then, it is checked whether the valid flag corresponding to the file in the MS cache management table 800 is ON. If the valid flag is ON, MS
The cache 1400 indicates that this file has been cached. In this case, proceed to 925.
If the valid flag is OFF, the MS cache 14
Since 00 indicates that it is not cached,
To place in the ES cache, at 940, the ES
The reference count and update count fields corresponding to the file in the cache monitor management table 1400 are cleared to zero. Then, at 945, a procedure for staging to the ES cache 1650 is taken. Specifically, the valid flag corresponding to the file in the ES cache monitor management table 1400 is turned ON. After these procedures are completed, the process proceeds to 925.

Next, as a third embodiment, a case where the present invention is applied to a computer system having a cluster configuration will be described with reference to FIG.

FIG. 7 is composed of two computers 100 and 100-1.

The two computers share the ES 1600 and the disk 1800. In particular, disc 1800
Are shared via the disk controller 1700.
MS caches (1400 and 1400-1) are provided in the memories (300 and 300-1) on each computer, respectively, to cache data. Further, an ES cache 1650 is prepared for the shared ES 1600, and a disk cache 1750 is prepared for the disk control device 1700, which is shared and used by 100 and 100-1.

In this computer system configuration, the data consistency between the MS cache 1400 and the MS cache 1400-1 is determined by the MS / ES cache processing 15
00 and the MS / ES cache monitor process 1500-1 are guaranteed by using communication means between computers.

Next, the relationship between the computer 100 and the computer 100-1 will be described. These two computers are in a master-slave relationship. Computer 100 is the master and computer 1
00-1 is a slave. The slave computer 100-1 has an MS cache report process 1100 and an ES cache report process 1200.
Are provided.

MS Cache Report Processing 1100
Each time the MS / ES cache processing 1500-1 performs a data operation or a data search on the MS cache 1400-1 in response to a data access request, the MS / ES cache processing 1500-1
It is called from the ES cache processing 1500-1. Then, for the file registered in 800-1, the number of times of reference and the number of updates are counted, and the file is periodically reported to the MS cache monitor 700, which is the master. Also, M
The S cache monitor 700 issues a staging or destaging request to the MS cache to the MS / ES cache processing 1500-1 in response to a staging or destaging instruction to the MS cache in file units.

ES Cache Report Processing 1200
Indicates that the MS / ES cache processing 1500-1 executes the ES cache 1650-1 in response to a data access request.
Each time you perform data search or data search, MS
/ ES cache processing 1500-1.
Then, for the file registered in 1000-1,
The number of times of reference and the number of updates are counted, and the count is periodically reported to the ES cache monitor 700 which is the master.

On the other hand, in the master side MS cache monitor processing 700, the information reported from the slave side MS cache report processing 1100 is registered in the MS cache monitor management table 800. Similarly, the ES cache monitor process 900 registers the information reported from the ES cache report process 1200 in the ES cache monitor management table 1000.

As described above, the embodiment of the present invention has been described in which the MS cache, the ES cache, and the disk cache are hierarchized and controlled. However, it is also possible to hierarchize the MS caches arranged on the hierarchized computer nodes and control the same.

[0083]

According to the present invention, in a computer system having a hierarchical cache area, a cache area to be used can be determined for each file in accordance with data access characteristics. As a result, when updating data, suppression of inter-processor communication that occurs to ensure data consistency, priority placement of data with a high reference ratio in a cache area with a high access speed improves the throughput of the database system, and response performance. Improvement can be achieved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a system representing a first embodiment.

FIG. 2 is a structural diagram of an MS cache monitor management table;

FIG. 3 is a flowchart of an MS cache monitoring process according to the first embodiment;

FIG. 4 is a configuration diagram of a system representing a second embodiment.

FIG. 5 is a flowchart of an MS cache monitoring process according to the second embodiment;

FIG. 6 is a flowchart of an ES cache monitoring process according to the second embodiment;

FIG. 7 is a configuration diagram when the present invention is applied to a cluster configuration system.

[Explanation of symbols]

Reference numeral 100: computer, 200: CPU, 300: main storage device, 400: user pro program, 500: monitoring process for MS cache in the first embodiment, 600
... MS cache monitor management table in the first embodiment, 700... MS cache monitor processing in the second embodiment, 800... MS cache monitor management table in the second embodiment, 900.
S cache monitor management table, 1000: ES cache monitor management table, 1100: MS cache report processing, 1200: ES cache report processing, 1300: MS cache processing, 1400 ...
MS cache, 1500: MS / ES cache processing, 1600: extended storage device, 1650: ES cache, 1700: disk control device, 1750: disk cache, 1800: disk.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G06F 12/08 557 G06F 12/08 557 3/06 302 3/06 302A 12/00 514 12/00 514K 15 / 16 645 15/16 645 (72) Inventor Chieko Akiba 5030 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Software Development Division, Hitachi, Ltd. Hitachi, Ltd. System Development Laboratory (72) Inventor Masaya Ichikawa 1099 Ozenji, Aso-ku, Kawasaki City, Kanagawa Prefecture F-term in Hitachi, Ltd. System Development Laboratory F-term (reference) 5B005 JJ13 KK02 KK13 MM11 PP11 QQ04 UU26 UU32 UU33 UU41 VV03 5B045 DD12 DD18 5B065 BA01 CE12 CH01 5B082 FA12

Claims (1)

[Claims] 1. One computer node is composed of two hierarchical nodes.
Registering a file identifier to which data to be allocated to each cache area belongs, in a cache control method having at least one cache area and allocating data accessed by a program operating on the computer node to the cache area; A step of preliminarily setting a ratio of a reference process of a file that uses each cache area to an update process as a target value; and A step of monitoring the number of requests and update requests, and an area where data belonging to a file whose ratio of the number of reference requests and update requests selected by the monitoring step does not satisfy the target value is stored. To cache data other than the file. Cache control method characterized by comprising the steps of: utilizing as an area for.