JPH09305473A - Caching system for retrieval system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a caching system which can retrieve information efficiency fast without requiring large memory capacity. SOLUTION: Information used in the process of narrowing-down retrieval, e.g. book list information, document list information, book/document detail information, thumbnail information, etc., are in hierarchical structure. At the stage wherein, for example, book list information of one upper layer is retrieved, information on a document list in a low layer of a book in the book list is retrieved in the background and also cached. While a conventional cache system stores obtained target information in a cache memory after the target information which is narrowed down to finally is displayed, this background caching makes precedent retrieval information in the layer below the upper layer in the background once the upper layer is retrieved and caches the information, so efficiency and speedy retrieval can be made.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a caching system for efficiently operating an image retrieval system.

[0002]

2. Description of the Related Art In an image search system consisting of a file server and a client connected on a network, there is known a technique for increasing the search speed by performing caching. For example, JP-A-6-19980
The technology described in Japanese Patent Publication, in order to search the image information at a practical speed, by storing the image information once searched in the memory of the client, when the same image information is searched again, We have realized an image search system that can search at a practical speed without sending a transfer request to a file server.

[0003]

The caching in the conventional image retrieval system as described above is performed when a document is browsed after being narrowed down to a specific document as a result of the retrieval, or whether the document is a target document. The image information is browsed in order to do so, but if the document to be searched is managed in a hierarchical structure such as a book (Book) and the documents (Document) that compose it, the user wants to search for the document. Before browsing the image information to narrow down the image, first search by book name or document name, and further narrow down to reach the final target document while referring to detailed information and thumbnails (reduced image information) of each book or document. It is a common practice to take steps such as.

Therefore, when a large number of terminals on the network perform a search, not only large-capacity image information but also list information of documents included in the book (part 43 in FIG. 4).
(Refer to FIG. 5), detailed information of each (refer to FIG. 5), and thumbnail information (refer to FIG. 6) are also transferred, which increases traffic on the network. Therefore, just by caching the image information once searched as in the conventional technique (Japanese Patent Laid-Open No. 6-19980), it is not always possible to carry out the entire search process at a practical speed. . Moreover, although cache of image information is effective for avoiding increase of traffic on the network, effective erasing means from the memory has not been considered. When high resolution and color image information will be handled in the future, there will be a problem that the client will have to prepare a large amount of memory unless effective means of erasing cache information is considered. To do.

An object of the present invention is to solve such a problem of the prior art. That is, the present invention
An object of the present invention is to provide a cache system that can efficiently and quickly search information in a search system that caches the search target information that has been displayed once when the client searches. Another object of the present invention is to provide a cache system that does not require a large capacity memory for the cache.

[0006]

According to the caching method of the present invention, in a search system consisting of a file server and a client connected on a network, when searching, not only the information of the search object that has been displayed once but also that search object is displayed. It has a cache means as a basic configuration which also caches information related to the search target information used in the process of narrowing down the information search. In the prior art, the cache is only the information to be searched, for example, the image information of the image in the image search system. However, the present invention uses the cache means to use the information, such as a book, in the process of narrowing down the search target information Since the list, document list, book / document detailed information, thumbnail information, etc. are also cached, it is possible to reduce traffic on the network and perform quicker search.

Further, in the present invention, in the caching method having the basic structure, the information related to the information to be searched has a hierarchical structure, and the cache means is capable of searching an upper layer of the hierarchical structure. When performed, it has a background cache function of previously searching in the background and caching the information about the lower layer belonging to the upper layer obtained as a search result. Information used in the process of narrowing down, such as book list information, document list information, book / document detailed information, and thumbnail information, has a hierarchical structure. Search results for information in the upper layer, for example, search information for lower layers based on the search result for book list information, for example, by repeatedly searching for document list information held by a book, finally narrowing down to search target information, for example, image information. . In the process, when the book list information of a certain upper layer is searched, the information of the document list which is the lower layer of the book in the book list is searched and cached in the background. With the conventional cache method, after the target information finally obtained is displayed, the obtained target information is stored in the cache memory. However, in the background cache of the present invention, the upper layer is used. Since the information of the lower layer is searched in advance in the background and cached when the search is performed, efficient and quick search can be performed.

Further, in each of the above inventions, setting means for setting a cache priority for each information to be cached may be provided, and the information to be cached may be determined according to the set priority. For example, as shown in the cache level setting unit 71 of FIG.
If the information to be cached includes “image information”, “document list”, “detailed information”, “thumbnail”, etc., a priority is set for each piece of information. By doing so, important information can be preferentially cached and the cache memory with a limited capacity can be effectively used.

Further, the background cache means may be configured to set a threshold value for performing background cache for each type of cache information and determine whether to perform background cache based on the threshold value. it can. For example, as shown in the background cache setting unit 73 in FIG. 7, the number of documents in the book is set as a threshold when the document list is background cached, and the number of documents in the book is set when the background thumbnail thumbnail of the book is cached. A threshold value is set, and the number of pages in the document is set as the threshold value when the thumbnail of the document is cached. When the threshold value is exceeded, the information is cached. As a result, information that has a large effect of being cached is selectively cached in the background.

Further, according to the present invention, in each of the above inventions, there is provided means for setting a standard for selecting information to be erased when erasing the cache information from the memory, and the cache means is provided in accordance with the set standard. A configuration having a function of erasing cache information can be adopted. As a standard for selecting the erasure target information, there are attributes of the target information such as the number of times of reference and reference time, or a priority set for each attribute. According to the present invention, the cache information to be erased is selected based on the criteria set in this way, so that the memory can be effectively used.

In the basic structure of the present invention, the information related to the search target information includes document list information of books, detailed information of books and documents, and thumbnail information, and the cache means is a target. It can be configured to clear cached information from memory when a book or document is cleared from the list. When you execute a search, the search results displayed on the list of books or documents will be cleared. The clearing can be used as a trigger to determine the cache information to be erased, and it is possible to realize an effective memory erasing means that has not been available in the past.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows an example of a schematic configuration of the entire image retrieval system according to the present invention. This image retrieval system includes at least one client 21, a file server 22, and a print server 23 as shown in FIG.
Are constituted by a network connected by a communication line 24. Network is Ethernet, AT
M, wireless, etc. are conceivable, but any of them can be applied. The file server 22 manages image data files and searches for image files in response to a request from the client 21. The print server 23 manages image printing according to a request.

FIG. 1 shows an example of the configuration of a client device having the features of the present invention in the image retrieval system of FIG. The client device creates an input section 11 such as a keyboard or a mouse for inputting a search instruction, a display section 12 for displaying necessary information, and a search execution instruction input by the input section 11 to create search information. And a cache related information setting unit 14 for setting cache related information such as cache level, deletion level, background cache, and deletion by list clear
A memory 15 for storing necessary information such as cache information and setting contents of cache-related information, and a search instruction section 13
The search execution unit 16 which receives the search instruction information from the memory 15 and searches the cache information in the memory 15 and the search request to the file server when the cache is not cached, the file server 22 and the print server 2.
3, a communication control unit 17 that communicates with each other via a network, a cache execution unit 18 including a background cache execution unit 181 that performs processing for cache in the background, and an internal bus 19.

FIG. 3 shows an example of the internal structure of the cache area of the memory 15 shown in FIG. The cache area includes an image information cache area 31, a document list cache area 32, a detailed information cache area 33, and a thumbnail cache area 34. The image information cache area 31 holds a large number of cached image information and unit information 35 including attribute information thereof. The unit information 35 is “information of corresponding book / document”, which is individual information such as an ID number indicating correspondence of which book / document information, and the number of times the cache information is displayed on the display (display unit). Is the "reference count",
Information such as "reference date and time", which is the latest date and time when the cache information was displayed on the display, and "list display" indicating whether the book or document linked to the cache information is currently displayed on the list. It consists of In the prior art, the cache area caches only the image information that has been displayed once, but in the present embodiment, the document list information of the book, the detailed information of the book and the document, and the thumbnail information are also cached in the memory. It is configured.

FIG. 4 shows an example of a search screen displayed on the display unit 12. The search screen includes search condition instructions, search execution instructions, thumbnail information display instructions, detailed information display instructions, and the like. An input unit 41 having an input unit, and a search information display unit 42 for displaying a search result according to the instruction of each display.
Consists of In the example of FIG. 4, a list of books and documents is displayed.

FIG. 5 shows an example of the document detailed information display screen displayed on the display unit 12, and each detailed information of the document as illustrated is displayed. This example shows the information that appears on the display screen when the document “I can do something like this” is selected on the search screen in FIG. 4 and an instruction to display detailed information is given.
With this detailed information, it becomes easy to determine whether or not the information is obtained by the search.

FIG. 6 shows an example of a thumbnail display screen 61 for displaying thumbnails of image information contained in the document displayed on the display unit 12, and a plurality of pages of reduced image information are simultaneously displayed on this display screen. Is displayed. This allows the user to roughly estimate the content of the document, which is useful for searching.

FIG. 7 shows an example of the cache-related information setting screen displayed on the display unit 12 provided by the client, and the user sets the cache-related information through this interface. The setting screen includes a cache level setting unit 71, a deletion level setting unit 72, a background cache setting unit 73, and other setting units 74 to 77.

The cache level can be set or not depending on whether or not the "Set cache level" button 711 in the cache level setting section 71 is checked. When setting the cache level, each cache information, that is, "Image information""Documentcolumn""Detailedinformation""Thumbnail"
Priority is set for each item. Information having a lower priority is targeted for erasure earlier when the memory is full.

A button 721 for "setting the erasing level" in the erasing level setting section 72 is a setting button for setting / not setting the erasing level corresponding to each cache information. When setting the erasing level, the erasing priority is set for each attribute information of each cache information file, that is, "reference count", "is list displayed", "reference time" and the like. From the attribute information having a low priority, it becomes the erasure judgment standard when the memory is full.

Background cache setting unit 73
The button of "perform background cache" in is a setting button for executing / not executing the background cache function. When executing the background cache function, a threshold for executing / not executing the background cache is set in each target cache information. For example, in the case where the search result displays a book list, only the books having the number of documents equal to or more than the threshold value are targeted for the background cache.

The setting button 74 for "clear cache information by clearing from list" uses the function of deleting the corresponding cache information when the list display of books and documents is cleared from the display screen. Whether or not to set.

The operation of the search system of the embodiment of the present invention configured as above will be described. FIG. 8 shows FIG.
3 is a flowchart showing the operation of the message processing unit 10 of the device. In order to perform a search, a search screen as illustrated in FIG. 4 is displayed on the display unit 12, and the user inputs cache-related information and search conditions by using the search screen and the input unit 11 such as a keyboard and a mouse. And perform a search execution instruction. The cache-related information setting means 14 is the input unit 1
The input information from 1 is stored in the memory 15 as setting information. That is, the cache-related information setting means 14 displays an interface for setting cache-related information as shown in FIG. 7 on the display unit 12, and the user can set the cache level and the deletion level and the priority, and the background cache. And setting of threshold value, various settings such as setting as to whether or not cache information is deleted by clearing from the list, etc. are performed as necessary.

Further, a search screen as shown in FIG. 4 is displayed on the display unit 12, and the user uses the search condition input unit 41 to
"Classification name", "Book name", "Document name", "Created date", "Author name" and other desired attributes of the search target are input as necessary, and "Thumbnail display"
When "display detailed information" is required, it is also specified. Then, by designating the "search execution" button, the information of these input search conditions is obtained by the search instruction unit 1.
Incorporated by 3. Then, the search instruction unit 13 notifies the search execution unit 16 of the input search condition information (step S801).

Receiving it, the search execution unit 16 determines the cache type (image information / document list / thumbnail information, etc.) from the search condition information (step S80).
2). According to the determination, the search execution unit 16 further searches whether the information on the search condition of the corresponding cache type is stored in the memory (step S803). And
It is checked whether the information matching the search condition information is in the cache area of the memory (step S804). If the corresponding information is stored in the memory, the memory 1
The information is read from 5 and displayed on the display 12 (step S806). After that, the reference count of the cache information, the reference date and time, and each sub information in the list display are updated (step S807).

Further, when the information of the search condition of the corresponding cache type is not stored in the memory, first, the sub-information during the list display of the cache information linked to the contents displayed so far is updated. After that, the search execution unit 16 accesses the file server 22 via the communication control unit 17 and executes the search (step S80).
9). Then, the search result is displayed on the display (step S810). Then, the image information of the search result is stored in the memory 15 (step S811). Further, the reference count, the reference date and time, and each piece of sub-information being displayed in the list are also stored in the memory 15 (step S812).

According to the caching method of the embodiment described above, not only the image information once displayed, but also the document list information held by the book, the detailed information held by the book or the document, and the thumbnail information are stored in the respective memory types. The cache area is cached accordingly. As described above, the document to be searched is, for example, a book (Book) and its constituent documents (Do).
If the document is managed in a hierarchical structure such as document), the user first searches by the book name or document name before browsing the image information to narrow down the documents to be searched, and further narrows down each book or The conventional method is to take a procedure of reaching the final target document while referring to the detailed information and thumbnail of the document. At that time, although only the image information was cached, the caching of information other than the image information was not performed as in the above-described embodiments of the present invention.
In the present embodiment, the caching of various information, which has not been performed conventionally, can be performed, so that the traffic on the network can be reduced and the search can be performed more quickly.

Next, the background cache execution unit 181 searches in the background in advance the document list information of the book excluding the image information, the detailed information of the book or the document, and the thumbnail information before being displayed on the display. It is for caching. FIG. 9 is a flowchart of the background cache process, which is a process that enters the part of the flowchart of FIG. The background cache execution unit 181 checks whether or not the background cache function is set after the update and storage of each cache information is completed by the processing of FIG. 8 (step 901). If not set, the process ends without doing anything. If the background cache is set, the search result is received from the search execution unit 16 that has performed the search with the previous search condition (step S90).
2) It is determined whether the search result is a book list display (step S903).

When the search result is the book list display, the threshold value of the number of documents in the book when the document list information in the book is background cached is read from the memory (step S904). The read threshold value is compared with the number of documents included in the book read as the search result when the search is performed first (step S905). If the number of documents is greater than or equal to the threshold value, the document list cache area 32 already in the memory 15
Is stored in the memory (step S90).
6). Only when the file is not stored in the memory 15, the file server 22 is accessed in the background via the communication control unit 17, and the document list information of the book that the number of documents is not less than the threshold value and is not cached is executed. (Step S907), the search result is stored in the document list cache area 32 of the memory 15.
(Step S908). As described above, by the processing from step S903 to step S908,
When the book list is searched, the background cache for the document list that is the lower hierarchy is selectively performed. The threshold, which is the criterion for selecting a new cache in this example, is determined appropriately based on the fact that the more documents in the book, the greater the effect of caching in the background. is there.

Next, the threshold value of the number of documents in the book when the thumbnail information in the book is background cached is read from the memory 15 (step S90).
9). The read threshold value is compared with the number of documents included in the book read as the search result when the search is performed first (step S910). If the number of documents is equal to or larger than the threshold, it is determined whether or not the document is already stored in the thumbnail cache area 34 in the memory 15 (step S911). If it is not stored in the thumbnail cache area 34 in the memory 15, the file server 22 is accessed through the communication control unit 17 in the background, and the number of documents is equal to or larger than the threshold value, and the book is not cached yet. The thumbnail information search is executed (step S912), and the search result is stored in the memory 15
It is stored in the thumbnail cache area 34 (step S913). In the processing from step S909 to step S913 described above, after the cache processing of the document list is performed, the thumbnail information (for example, the first document of the first document in the book) that is in the lower hierarchy of the document is held. Background cache for page thumbnail information) is selectively performed.

After the background cache processing of the thumbnail information held by the book and when the search result is the document list display, the thumbnail information in the document is background cached from the memory 15. Therefore, first, the threshold value for background caching of the thumbnail information represented by the number of pages of the document is read (step S914).
The read threshold value is compared with the number of pages of the document read as the search result when the search is performed first (step S915). If the number of pages in the document is equal to or larger than the threshold value, it is determined whether or not the page is already stored in the thumbnail cache area 34 in the memory 15 (step S
916). When the number of pages is equal to or larger than the threshold and is not stored in the thumbnail cache area in the memory 15, the file server 22 is accessed through the communication control unit 17 in the background to search the thumbnail information of the document. The search result is executed (step S917), and the search result is stored in the thumbnail cache area 34 of the memory (step S918). If there are multiple search results,
The above process is repeated.

As described above, when the documents are managed in a hierarchical structure, the user can narrow down the documents to be retrieved by
Considering the case where the search is performed by the book name or document name, and then the final target document is reached while referring to the detailed information or thumbnail information of each book or document to further narrow it down, the background explained in FIG. 9 is considered. In the cache process, the lower layer data to be searched next can be searched and cached in advance, so that efficient and quick search can be performed.

Next, FIG. 10 is a flowchart showing a process for efficiently erasing the cached information, and this process is a process executed by the search execution unit 16 in the part of the flowchart of FIG. The information set from the memory 15 by the button 74 “Clear from list and delete cache information” on the setting screen of FIG. 7 is stored in the memory 15. Memory 1
5, it is determined whether or not it is set to be erased (step S1001), and if it is set to be erased, the cache information related to the target book or document that has been displayed up to that point is erased (step S1001). S1002). When you execute a search on the client, the search results displayed on the list of books or documents will be cleared. The clearing can be used as a trigger to determine the cache information to be erased, and it is possible to realize an effective memory erasing means that has not been available in the past.

FIG. 11 shows a flow chart of a specific example of the processing of storing the search result in the memory in step S811 of FIG. When storing various cache information (search results) in the memory, the search execution unit 16 or the background cache execution unit 181 first compares the information to be stored with the remaining amount of the memory and checks whether the storage is possible (step S1101). ~ S1102). If it can be stored, it is stored in the memory (step S1108).

If the remaining amount is too small to store the data, it is first read from the memory whether the cache level is set (step S1103). The cache level is set by checking the "Set cache level" button 711 of the cache level setting section 71 as shown in the cache related information setting screen of FIG. Remembered in. At that time, priority is assigned to each cache information such as image information, document list, detailed information, thumbnails (1 to 1).
4) is set. When cache information with a lower priority has a smaller amount of remaining memory, it is targeted for deletion earlier.

If the cache level has been set, then what is the lowest priority cache information than the memory is read (step S1104), and it is determined whether or not there is corresponding cache information (step S1).
105). If there is corresponding cache information, the cache information is deleted (step S1106). After the erasure, it is determined whether the remaining capacity of the memory can store the cache information (step S1107), and if the result of the determination indicates that the cache information can be stored, the storage in the memory is executed (step S1108). When it is determined that the remaining amount of memory cannot store the cache information, the process returns to step S1105 and it is determined whether there is information that can be erased again. If there is no erasable information and the currently erased information does not have the highest priority, the information with the next lowest priority is read from the memory (steps S1109 to S1110).
If there is information to be erased, it is erased (steps S1105 to S1).
106). This operation is repeated until the area where the cache information can be stored in the memory becomes empty or there is no information to be erased, that is, the area cannot be secured even if the highest priority information is erased. If there is no information to delete, do not cache. If the cache level is not set, the corresponding information is sequentially deleted regardless of the type of cache information (steps S1111 to S1112).

As in the process of FIG. 11, the user can set the priority for each type of cache information, and the storage of the cache information is controlled by the set priority, which is efficient and effective. Utilization of memory can be realized.

FIG. 12 is a flow chart showing an example of details of the processing of step S1106 or step S1112 of FIG. If there is more than one piece of information to be erased, it is necessary to select and erase it by some method. One method is to erase the oldest information in order, but as shown in FIG. There is also a way to erase. When erasing certain cache information from the memory 15, the search execution unit 16 or the background cache execution unit 181 first reads from the memory 15 whether the cache information deletion level is set (step S1).
201). The erasure level is set to the erasure level setting section 72 as shown in the cache related information setting screen of FIG.
The setting is made by checking the "Set erase level" button 721 of, and the setting is made in the memory 15
Is stored. At that time, the priority (1 to 3) is set to the attribute of the cache information file, for example, the number of times of reference, whether a list is being displayed, or reference date and time. The deletion information is targeted from the attribute information having a low priority.

If the erase level is not set, the oldest cache information is erased regardless of the determined type or the type (step S120).
2). If the erase level has been set, the memory 15
What is the attribute type with the lowest priority is read (step S1203), and it is determined whether or not there is corresponding cache information. If there is, cache information of that attribute is erased and the process ends (step S1205). If there is no cache information to be erased and the attribute currently being erased does not have the highest priority, the attribute with the next lowest priority is read from some memory and it is determined whether or not there is corresponding cache information. ~ S1207, S1
204). This operation is repeated until information to be deleted is found or even if the attribute having the highest priority is checked, there is no information to be deleted. If there is no information to be deleted, the process ends. Since the user can set the priority of whether or not to erase each type of cache information, efficient and effective utilization of the memory can be realized.

[0040]

INDUSTRIAL APPLICABILITY According to the present invention, information used in the process of a narrowed search when searching the information to be searched by the cache means, for example, a book list, a document list, a book /
Since detailed information of documents, thumbnail information, and the like are also cached, traffic on the network can be reduced and search can be performed more quickly.

According to the background cache of the present invention, when the upper layer is searched, the information of the lower layer is searched in advance in the background and cached, which is efficient and quick. Search is possible.

Further, according to the configuration of the present invention, which is provided with the setting means for setting the priority of caching for each information to be cached, important information can be preferentially cached, and a limited capacity is required. The cache memory can be used effectively.

Further, according to the configuration of the background cache means of the present invention, which determines whether or not to perform the background cache based on the threshold value, the information which has a great effect of being cached is selectively backed up. It will be cached in the ground, which enables efficient searches.

Further, according to the configuration of the present invention in which the means for setting the standard for erasing the cache information from the memory is provided, the cache information to be erased is selected based on the set standard, so that the memory is effectively utilized. be able to.

Further, according to the configuration of the present invention, the cache information related to the search result displayed on the list of the book list or the document list is cleared when the search result is cleared. An effective memory erasing means can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a client device having the features of the present invention in an image search system;

FIG. 2 is a diagram showing a schematic configuration example of an entire image search system according to the present invention,

FIG. 3 is a diagram showing an example of an internal structure of a cache area of the memory in FIG.

FIG. 4 is a diagram showing an example of a search screen displayed on the display unit of the client,

FIG. 5 is a diagram showing an example of a document detailed information display screen displayed on the display unit,

FIG. 6 is a diagram showing an example of a thumbnail display screen displaying thumbnails of image information included in a document displayed on the display unit of the client;

FIG. 7 is a diagram showing an example of a cache related information setting screen displayed on the display unit of the client;

8 is a flowchart showing the operation of the processing unit 10 of the apparatus shown in FIG.

FIG. 9 is a flowchart of background cache processing,

FIG. 10 is a flow chart showing a process for efficiently erasing cached information, which is part of the flow chart of FIG.

FIG. 11 is a flowchart of a specific example of a process of storing a search result in the memory in step S811 of FIG.

FIG. 12 is a flowchart showing an example of details of processing in step S1106 or step S1112 in FIG.

[Explanation of symbols]

11 ... Input part, 12 ... Display part, 13 ... Search instruction part, 14
... cache-related information setting unit, 15 ... memory, 16 ... search executing unit, 17 ... communication control unit, 18 ... cache executing unit, 181 ... background cache executing unit.

Claims (6)

[Claims] 1. In a search system comprising a file server and a client connected to a network, when performing a search, not only the search target information that has been displayed once, but also the search target information used in the process of narrowing down the search A caching method characterized in that a cache means for caching information related to search target information is also provided. 2. The information related to the search target information has a hierarchical structure, and the cache unit belongs to an upper layer obtained as a search result when an upper layer of the hierarchical structure is searched. 2. The caching method according to claim 1, further comprising a background cache function of previously searching and caching information regarding lower layers in the background. 3. The setting means for setting the priority of caching is provided, and the caching means has a function of determining the information to be cached according to the set priority. The described caching method. 4. A means for setting a threshold value for performing background cache for each type of cache information, and the background cache means for determining whether or not to perform background cache based on the threshold value. The caching method according to claim 2, further comprising: 5. A means for setting a criterion for selecting information to be erased when erasing the cache information from the memory is provided, and the cache means has a function of erasing the cache information according to the set criterion. The caching method according to any one of claims 1 to 4, wherein: 6. The information related to the search target information includes document list information held by a book, detailed information held by the book and the document, and thumbnail information, and the cache means clears the target book or document from the list. The caching method according to any one of claims 1 to 4, wherein the caching method has a function of erasing corresponding cache information from the memory in the event of a failure.