JP2011028658A - Database device, cache device, database system, cache maintenance method and program thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the load of cache maintenance processing in a database system. <P>SOLUTION: The database device obtains the latest cache entry on a cache 231 by a cache track part of the cache device 200, and records it on a cache management table 1312. The database device refers to the cache management table 1312, upon update processing of the a base table 1311, to identify data on the base table 1311 which is affected by the update processing of the base table 1311 and exists on the cache 231. The database device transmits a destruction message for the cache entry of the identified data to the cache device 200. The cache device 200 destroys the cache entry on the cache 231 designated by the destruction message. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a cache maintenance technique for maintaining a cache entry of data in a database.

  Today, with the explosion of the Internet, many services are provided through the Internet. Examples of services provided through the Internet include online shopping, online banking, social networking service (SNS), and the like. In most cases, a system that provides these services includes a database (DB) that stores data such as user account information, product information, and posted articles by the user, and an application. This application issues a query to the database in accordance with the service, and creates a result to be presented to the user by using data returned from the database.

In these systems, if the number of accesses to the database increases significantly due to an increase in the number of users, etc., the database bandwidth and CPU (Central Processing Unit) resources may be exhausted, resulting in performance degradation and server down. . In these systems, even if the number of accesses does not increase, if the query to the database is complicated, it takes a long time to return the query result.

  Therefore, as a technique to solve the above-mentioned database processing load and reference performance problems, it was created by using this database query result in a storage area (cache) that can be accessed at high speed separately from the database. Data is being stored.

  Here, when acquiring data from the cache, the application checks whether the necessary data exists on the cache. If the data does not exist in the cache, the data associated with the request from the user is stored in the cache at the same time as obtaining the data from the database. Thereafter, when the same data is needed, the application reads this data from the cache and uses it. This eliminates the need to access the database, so that a system using a cache can make it possible to refer to data at high speed and reduce the number of accesses to the database to reduce the load on the database.

  On the other hand, when the cache is used, if update processing (registration, update, deletion) occurs in the database, inconsistency may occur between the data stored in the cache and the data stored in the database. For example, when referring to data updated in the database in the cache, the data stored in the cache is not updated, and thus the application refers to old data before update.

Conventionally, in order to solve this problem, a cache maintenance technique for maintaining cache consistency when a database is updated has been proposed.

  As this technique, one that discards the cache has been proposed (see, for example, Non-Patent Document 1). In the method described in Non-Patent Document 1, when an update that causes inconsistency in the cache is performed on the database, the database transmits a discard message to the cache, and inconsistency occurs in the cache. Data to be discarded is prevented, and data before update stored in the cache is prevented from being referred to.

  In addition, a re-inquiry method has also been proposed in which all data stored in the cache is replaced and kept up-to-date by making an inquiry to the database again after discarding the cache (see, for example, Non-Patent Document 2).

Greg Barish, Katia obraczka, “World Wide Web Caching: Trens and techniques”, IEEE Communications Magazine 2000.5 James Gwertzman, Margo Seltzer, “World Wide Web Cache Consistency”, USENIX technical Conference, 1996

  However, in any of the above-described techniques, the database has to send a discard message to the cache each time an update that causes inconsistency in the cache is performed on the database, which increases the processing load. In addition, the database seeks a cache to be a target of the discard message based on the update contents of the database and the database. For this reason, it is necessary for the database to identify a cache entry that does not actually exist in the cache and to transmit a cache entry discard message, and the processing load of cache maintenance is large.

  Therefore, an object of the present invention is to solve the above-described problems and reduce the load of the cache maintenance processing of the database.

  In order to solve the above-described problems, the present invention provides a database system having a cache device that stores a cache of data read from a database device, and a database device connected to the cache device via a network. When the database device data update process is performed, the database device transmits a cache discard message in the cache device via the network, and the base table for storing the data and the data stored in the base table, A cache management table indicating data having cache entries is stored in the cache. The database device includes an input / output unit that controls transmission / reception of various information to / from the cache device via the network, and when a base table update process occurs, the cache management table and the update process contents of the base table Referring to the above, among the data affected by the update process of the base table, data having a cache entry in the cache is specified. Next, the database device transmits a cache entry discard message for the specified data to the cache device. When cache update information is received in the cache device, the cache management table is updated based on the update information.

  When such a database table update process occurs, such a database apparatus identifies data having a cache entry on the cache among data affected by the update process. Then, the database device transmits a cache entry discard message for the specified data to the cache device. In other words, the database device transmits a discard message for the cache entry existing on the cache of the cache device, so that it is not necessary to specify a cache entry that does not actually exist on the cache. Further, a useless discard message is not transmitted. Therefore, it is possible to reduce the processing load of cache maintenance by the database device.

  According to the present invention, a cache device in a database system including a database device includes a cache track unit that monitors cache update processing and transmits cache update information to the database device via a network.

  In this way, when the cache of the cache device is updated, the database device can receive the update information from the cache device, so that the latest cache entry existing on the cache can be grasped.

  According to the present invention, there is provided a database system including at least one of the above-described database device and a cache device.

  By doing so, it is possible to realize a database system that reduces the processing load of cache maintenance by the database device.

  In the present invention, the cache maintenance method is a program for causing a database device, which is a computer, to execute.

  By doing so, it is possible to cause a general database device to execute the above-described cache maintenance method.

  According to the present invention, it is possible to reduce the load of cache maintenance in a database.

It is the figure which showed the structural example of the database system of this Embodiment. It is the figure which showed notionally the outline | summary of the database system of FIG. (A) is the figure which illustrated the base table of FIG. 1, (b) is the figure which illustrated the query for cache creation. It is the figure which illustrated the cache management table of FIG. It is the figure which illustrated the cache of FIG. It is the figure which showed the process sequence of the database apparatus of FIG. It is the figure which showed the detailed flow of the process (S330) at the time of base table update of FIG. FIG. 6 is a diagram for explaining an example of cache entry identification processing affected by the base table update processing of FIG. 1; FIG. 8 is a diagram showing a detailed flow of a base table narrowing-down process (S420) in FIG. 7; It is the figure which showed the example of the narrowing-down process of the base table of FIG. (A) is the figure which illustrated the inquiry of narrowing down the base table by the cache management table of FIG. 1, (b) is the figure which illustrated the narrowing-down result. It is the figure which showed the structural example of the database system of this Embodiment.

  Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described. First, the outline of the database system according to the present embodiment will be described with reference to FIG. The database system includes a database device 100, a cache device 200 including a cache 231, and a terminal device 300 that transmits a data update request or read request of the database device 100. The database device 100, the cache device 200, and the terminal device 300 are connected by a network 400 such as the Internet. The cache 231 of the cache device 200 stores data (cache entry) created using the read result from the terminal device 300 to the database device 100. When the terminal device 300 reads data from the cache 231, the terminal device 300 determines whether or not the data exists in the cache 231. If there is no data, the terminal device 300 reads data from the database device 100. Then, the cache device 200 stores data (cache entry) associated with the request from the terminal device 300 in the cache 231. Thereafter, if the request from the terminal device 300 is a request for the same data, the cache entry of the data is read from the cache 231 and used. Details of this database system will be described later.

  Next, an outline of the operation of such a database system will be described with reference to FIG. First, when the database apparatus 100 of the database system receives an update request for the base table 1311, (1) among the data of the base table 1311, the data having a cache entry on the cache 231 of the cache apparatus 200 is narrowed down. Here, data having a cache entry on the cache 231 is recorded in the cache management table 1312. Therefore, the database apparatus 100 can determine which data in the base table 1311 should be narrowed down by referring to the cache management table 1312. For example, if there is a record of key value = d, e, f in the cache management table 1312, based on this, the data in the base table 1311 may be narrowed down to data having this key value = d, e, f. I understand that.

  Next, (2) the database apparatus 100 refers to the contents of the update process of the base table 1311 and identifies data affected by the update process of the base table 1311. For example, if the content of the update process is that the data of “auther_uid = b” is inserted into the base table 1311, the data affected by the update process is data having to_uid = b of the base table 1311. Therefore, data having to_uid = b (data having from_uid = d, f) is specified from the data in the base table 1311 narrowed down in (1).

  (3) The database device 100 refers to the data specified in (2), creates a list of key values of cache entries to be discarded from the cache 231 (for example, key value = d, f), and cache device 200. Thereafter, the cache device 200 discards the cache entry shown in this list from the cache 231. For example, when the cache device 200 receives a list (discard message) indicating the key value = d, f from the database device 100, the cache device 200 discards the cache entry having the key value d, f from the cache 231.

  As described above, when the update process of the base table 1311 occurs, the database apparatus 100 identifies data having a cache entry on the cache 231 among the data affected by the update process, and discards the cache entry of this data. The message is transmitted to the cache device 200. That is, since the database apparatus 100 transmits a discard message for the cache entry existing on the cache 231 of the cache apparatus 200, it is not necessary to specify a cache entry that does not actually exist on the cache 231. In addition, a useless discard message is not transmitted. Therefore, it is possible to reduce the processing load of cache maintenance by the database device.

Next, returning to FIG. 1, the configuration of the database system will be described in detail.
<Database device>
The database apparatus 100 is realized by a computer that can communicate via the network 400, and includes an input / output unit 110, a storage unit 130, and a processing unit 120. The input / output unit 110 receives an input of an update request or read request for the base table 1311 of the database device 100 from the terminal device 300 or the like via the network 400, or transmits a cache entry discard message on the cache 231. It is an interface to do. The storage unit 130 includes a database unit 131 including a base table 1311 and a cache management table 1312. The processing unit 120 controls the entire database apparatus 100. In this case, after the update of the cache management table 1312 and the update process of the base table 1311, mainly the data affected by the update process is specified. A discard message for the cache entry of this data is transmitted to 200.

  The input / output unit 110 includes a communication interface and an input / output interface. The processing unit 120 is realized by a program execution process by a CPU (Central Processing Unit) included in the database apparatus 100, a dedicated circuit, or the like. Further, the storage unit 130 includes a storage medium such as a random access memory (RAM), a read only memory (ROM), a hard disk drive (HDD), and a flash memory. When the function of the processing unit 120 is realized by program execution processing, the storage unit 130 stores a program for realizing the function of the database device 100.

  The storage unit 130 includes the database unit 131 including the base table 1311 and the cache management table 1312 as described above.

  The base table 1311 is a table that stores one or more data. There may be a plurality of base tables 1311 such as a message table and a follower table shown in FIG. Note that the message table shown in FIG. 3A is a table indicating the authenticator_uid (creator) and body (body) of the message for each message_id. The follower table is a table indicating to_uid (message transmission destination user) for each from_uid (message transmission source user). For this base table 1311, the base table processing unit 121 creates, for example, a query shown in FIG. 3B as a cache creation query (query for creating a cache entry stored in the cache 231). . This cache creation query is a prepared query with [UID] as a parameter. From the message table and follower table, the from_uid of the follower table is [UID] (specified user ID) data, and the data Is a query that searches for the message_id of the data whose to_uid is the same uid as the author_uid of the message table. Note that the attribute of the base table 1311 specified by a parameter (for example, [UID]) is referred to as a parameter attribute. In the above example, from_uid of the follower table is a parameter attribute.

  The cache management table 1312 in FIG. 1 is information indicating cache entries existing on the cache 231 of the cache device 200. The cache management table 1312 is information indicating the key value of the cache entry existing on the cache 231 as shown in FIG. The cache management table 1312 is referred to when the cache entry specifying unit 123 (described later) narrows down data in the base table 1311.

  The processing unit 120 in FIG. 1 includes a base table processing unit 121, a cache management table updating unit 122, a cache entry specifying unit 123, and a cache maintenance unit 124.

  The base table processing unit 121 receives an update request (update inquiry) or a read request for data of the base table 1311 from the terminal device 300 or the like via the input / output unit 110. In response to these requests, the base table 1311 is updated or read. Then, the base table processing unit 121 transmits the execution result to the cache device 200, and the cache device 200 adds a cache entry on the cache 231. Note that the update request (update inquiry) is, for example, INSERT, UPDATE, DELETE, or the like for the base table 1311.

  The cache management table update unit 122 acquires information on the cache entry existing on the cache 231 by the cache track unit 223 (described later) of the cache device 200 and records this information in the cache management table 1312. That is, the cache management table 1312 is updated.

  The cache entry specifying unit 123 monitors the base table 1311. When update processing of the base table 1311 occurs, the update processing content (for example, the identification information of the updated base table 1311 and the record updated in the base table 1311) ) Is stored in a predetermined area of the storage unit 130. Then, with reference to the cache management table 1312 and the update processing content of the base table 1311, the cache entry related to the data to be updated is specified among the data stored in the cache 231. Specifically, the cache entry specifying unit 123 first refers to the cache management table 1312 and narrows down data (records) having a cache entry on the cache 231 among the data of the base table 1311. Then, the cache entry specifying unit 123 obtains the cache entry of the data affected by the update of the base table 1311 (for example, data having the same key value as the key value of the updated data) from the update processing contents of the base table 1311. Identify.

  The cache maintenance unit 124 transmits a discard message instructing the discard of the cache entry specified by the cache entry specifying unit 123 to the cache device 200. In addition, when the base table processing unit 121 updates or reads data in the base table 1311 in response to a request from the terminal device 300, the cache maintenance unit 124 instructs addition of a cache entry indicating the execution result. An additional message is transmitted to the cache device 200.

<Cache device>
The cache device 200 includes the cache 231 of the database device 100, and a new cache entry is added (set), a predetermined cache entry is discarded (expire), and read (get) is performed on the cache 231. . The cache device 200 is realized by a computer that can communicate via the network 400, and includes an input / output unit 210, a storage unit 230, and a processing unit 220.

  The input / output unit 210 receives an input of a data update or read request from the terminal device 300 or the like via the network 400, or receives a cache entry discard message or an additional message, a cache in / out result (from the database device 100) This is an interface for outputting the update processing result of the cache 231). The storage unit 230 stores a cache 231. The processing unit 220 controls the entire cache device 200, and here, mainly adds or deletes cache entries in the cache 231 in accordance with instructions from the database device 100. Further, the processing unit 220 monitors the cache entry on the cache 231 and transmits the monitoring result to the database device 100.

  The input / output unit 210 includes a communication interface and an input / output interface. The processing unit 220 is realized by a program execution process by a CPU provided in the cache device 200, a dedicated circuit, or the like. Furthermore, the storage unit 230 includes a storage medium such as a RAM or an HDD. The cache 231 is formed on the RAM of the storage unit 230, for example. When the function of the processing unit 220 of the cache device 200 is realized by program execution processing, the storage unit 230 stores a program for realizing the function of the processing unit 220.

  The storage unit 230 includes a cache 231 including one or more cache entries. A cache entry is a storage unit in the cache 231. For example, as shown in FIG. 5, the cache 231 indicates the value (value) of data read using the key value (key value used for the data read request of the base table 1311) for each key value. Information. Here, the value for one key value is one cache entry.

  The processing unit 220 includes a cache processing unit 221, a cache update unit 222, and a cache track unit 223.

  In response to a request from the terminal device 300 or the like, the cache processing unit 221 reads a cache entry in the cache 231 and executes a process or the like. Then, the result is returned to the request transmission source. If there is no cache entry for the target data of the request on the cache 231, a message to that effect is returned to the request source.

  The cache update unit 222 discards (expires) the cache entry on the cache 231 in accordance with the discard message from the database device 100. When an addition message is received from the database apparatus 100, a cache entry is added (set) on the cache 231 accordingly. Note that the cache updating unit 222 may discard some cache entries when the total capacity of the cache entries on the cache 231 exceeds a predetermined amount. As an algorithm at this time, for example, LRU (Least Recently Used) or MRU (Most Recently Used) is used. In the following description, adding a new cache entry on the cache 231 is referred to as cache-in, and discarding a cache entry on the cache 231 is referred to as cache-out. In addition, cash-in or cash-out is collectively referred to as cash-in / out.

  The cache track unit 223 monitors the cache 231 and transmits information on cache entries existing on the cache 231 to the database device 100. For example, when the cache 231 is updated, the cache entry information on the cache 231 after the update process is transmitted to the database device 100. When the cache management table update unit 122 of the database device 100 receives the information on the cache entry, the cache management table update unit 122 records the information in the cache management table 1312.

<Processing procedure>
Next, the processing procedure of the database apparatus 100 of FIG. 1 will be described using FIG. First, the database apparatus 100 waits until an update of the base table 1311 or a cache update (cache in / out) of the cache 231 of the cache apparatus 200 occurs (S310), and detects an update of the base table 1311 (S310). The processing at the time of updating the base table 1311 is executed (“Update of base table occurs” in S320) (S330). That is, when the base table processing unit 121 of the database apparatus 100 receives an update process request for the base table 1311 from the terminal apparatus 300 or the like, and performs an update process for the base table 1311 based on this request, the process of S330 is executed. Then, the process proceeds to S350.

  On the other hand, when the database apparatus 100 detects the occurrence of update processing (cache in / out) of the cache 231 of the cache apparatus 200 (“cache update occurs” in S320), the cache management table update unit 122 of the database apparatus 100 The cache management table 1312 is updated (S340). That is, the cache track unit 223 of the cache device 200 monitors the cache in / out of the cache 231 and, when detecting the occurrence of the cache in / out, notifies the database device 100 of the cache in / out result. The cache management table updating unit 122 of the database device 100 records the information of the cache entry existing on the cache 231 in the cache management table 1312 (see FIG. 4) based on the cache in / out result.

  Then, the database apparatus 100 ends the process when there is an input of a process end command or the like (Yes in S350), and returns to S310 if there is no input of the end command or the like (No in S350).

  Next, details of the process (S330) at the time of updating the base table in FIG. 6 will be described with reference to FIG. First, the base table processing unit 121 of the database apparatus 100 in FIG. 1 receives an update of the base table 1311 (S410). Then, the base table processing unit 121 updates the base table 1311 based on this. Here, the cache entry specifying unit 123 monitors the base table 1311, and updates the processing contents of the base table 1311 (for example, updated identification information and updated records of the base table 1311) in a predetermined area of the storage unit 130. To remember.

  Subsequently, the cache entry specifying unit 123 of the database device 100 narrows down records (data) from the base table 1311 using the cache management table 1312 (S420). That is, the cache management table 1312 is used to narrow records relating to cache entries existing on the cache 231 from the base table 1311. Details of the record narrowing process will be described later.

  Next, the cache entry specifying unit 123 specifies a cache entry affected by the update of the base table 1311 (S430). That is, the cache entry specifying unit 123 selects the cache entry affected by the update process of the base table 1311 based on the update process contents of the base table 1311 stored in the storage unit 130 and the narrowing result of the base table 1311 in S420. Identify.

  For example, as shown in FIG. 8A, when the record indicated by reference numeral 1001 is inserted into the message table and the narrowed-down follower table data is the data indicated by reference numeral 1002 in S420 of FIG. For example, the entry specifying unit 123 issues a cache discarding query as illustrated in FIG. This cache discarding query is a prepared query that instructs to select a key value from the from_uid value of a record having the to_uid = b with the to_uid = b of the narrowed follower table as a parameter. Here, from the follower table, since the value of from_uid of the record having the value of to_uid = b is “d, f”, “d, f” is obtained as the identification result of the cache entry to be discarded.

  Returning to the description of FIG. After the cache entry specifying unit 123 specifies the cache entry in S430, the cache maintenance unit 124 transmits the discard message specified in S430 to the cache device 200 (S440). The cache device 200 that has received the discard message discards the cache entry indicated by the discard message. If the update process of the base table 1311 has not been completed yet (No in S450), the process returns to S410. If the update process of the base table 1311 has been completed (Yes in S450), the process ends.

  By doing so, the database apparatus 100 can cause the cache apparatus 200 to discard the cache entries that are affected by the update of the base table 1311 among the cache entries existing on the cache 231 of the cache apparatus 200. .

  Here, the details of the process of S420 in FIG. 7 will be described with reference to FIG. First, the cache entry specifying unit 123 of the database apparatus 100 in FIG. 1 reads the cache management table 1312 (S1010). That is, a list of key values of cache entries existing on the cache 231 is read. Then, the cache entry specifying unit 123 selects the base table 1311 including the parameter attribute (S1020). For example, since the parameter attribute in the cache creation query shown in FIG. 3B is from_uid of the follower table, the cache management table 1312 selects the follower table. Then, the selected record of the base table 1311 is selected (SELECT) based on the contents of the cache management table 1312 (S1030). For example, when the cache entry specifying unit 123 uses the cache management table 1312 illustrated in FIG. 10 to narrow down records in the base table 1311 (follower table), the base table 1311 as illustrated in FIG. Issue an inquiry. That is, a follower table is selected, and an inquiry for narrowing down records having the same value as the key value recorded in the cache management table 1312 is issued using the from_uid of the follower table as a parameter attribute. Based on this inquiry, a record of from_uid = d, e, f is searched from the follower table, and a narrowing result as shown in FIG. 11B is obtained.

  Returning to the description of FIG. When the cache entry specifying unit 123 of the database device 100 finishes processing of all the base tables 1311 (Yes in S1040), the cache entry specifying unit 123 ends the processing of S420. On the other hand, if there is a base table 1311 that has not been processed yet (No in S1040), the process returns to S1010.

  In this way, the cache entry specifying unit 123 can narrow down records in the base table 1311 to records relating to cache entries existing on the cache 231.

  According to the database device 100 described above, a cache entry discard message that actually exists in the cache 231 among the cache entries of data affected by the update process of the base table 1311 can be transmitted to the cache device 200. . In other words, the database device 100 does not need to send more cache entry discard messages than necessary to the cache device 200, so that the cache maintenance load on the cache 231 can be reduced.

  Note that a plurality of cache devices 200 in the database system may be provided as shown in FIG. In this case, the database device 100 receives the identification information of the transmission source cache device 200 and the cache in / out result of the cache 231 of the cache device 200 from the cache track unit 223 of each cache device 200, and performs cache management. The table 1312 is updated. As a result, in the cache management table 1312, the cache device 200 in which each cache entry exists is recorded along with information on the cache entry existing in each cache 231. By referring to such a cache management table 1312, the database apparatus 100 can transmit a discard message to the cache apparatus 200 having the cache entry.

DESCRIPTION OF SYMBOLS 100 Database apparatus 110,210 Input / output part 120,220 Processing part 121 Base table processing part 122 Cache management table update part 123 Cache entry specification part 124 Cache maintenance part 130,230 Storage part 131 Database part 200 Cache apparatus 221 Cache processing part 222 Cache update unit 223 Cache track unit 231 Cache 300 Terminal device 400 Network 1311 Base table 1312 Cache management table

Claims (5)

In a database system having a cache device having a cache of data read from the database device, and the database device connected to the cache device via a network, data update processing of its own database device is performed A database device for sending a cache discard message in the cache device via the network,
A storage unit for storing a base table for storing the data, and a cache management table indicating data having a cache entry in the cache among the data stored in the base table;
An input / output unit that manages transmission and reception of various information to and from the cache device via the network;
When the update process of the base table occurs, a cache entry is stored in the cache among the data affected by the update process of the base table with reference to the cache management table and the update process content of the base table. A cache entry specifying unit for specifying existing data;
A cache maintenance unit that sends a cache entry discard message for the specified data to the cache device via the input / output unit;
A database device comprising: a cache management table update unit that updates the cache management table based on the update information when cache update information in the cache device is received via the input / output unit. A cache device in a database system comprising the database device according to claim 1,
A cache device, comprising: a cache track unit that monitors the cache update process and transmits the cache update information to the database device via the network.   A database system comprising the database device according to claim 1 and one or more cache devices according to claim 2. In a database system having a cache device having a cache of data read from the database device, and the database device connected to the cache device via a network, data update processing of its own database device is performed A cache discard message in the cache device via the network, and a base table for storing the data, and cache management indicating data having a cache entry in the cache among the data stored in the base table A database device including a storage unit for storing a table,
When the update process of the base table occurs, a cache entry is stored in the cache among the data affected by the update process of the base table with reference to the cache management table and the update process content of the base table. Identifying the existing data;
Sending a cache entry discard message for the specified data to the cache device;
A cache maintenance method for executing a step of updating the cache management table based on the update information when cache update information is received in the cache device.   The program for making the said database apparatus which is a computer perform the cache maintenance method of Claim 4.

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