JP2976896B2 - Remote file cache device - Google Patents

Remote file cache device

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Publication number
JP2976896B2
JP2976896B2 JP8217972A JP21797296A JP2976896B2 JP 2976896 B2 JP2976896 B2 JP 2976896B2 JP 8217972 A JP8217972 A JP 8217972A JP 21797296 A JP21797296 A JP 21797296A JP 2976896 B2 JP2976896 B2 JP 2976896B2
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Japan
Prior art keywords
file
time
management information
expected value
remote
Prior art date
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Expired - Lifetime
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JP8217972A
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Japanese (ja)
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JPH1049422A (en
Inventor
直樹 柴多
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日本電気株式会社
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Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a remote file caching apparatus for caching a remote file obtained through a network in a local file storage unit for later access.

[0002]

2. Description of the Related Art A client that obtains and uses a remote file from a server or the like via a network, for example, the World Wide Web (World Wide Web)
When a client such as b) accesses a remote file via the network every time it is needed, the problem is that the remote file cannot be obtained quickly when the transfer speed of the network is low or the load on the server is heavy. Occurs. For this reason, a remote file cache is often provided on the client side to avoid these problems.

[0003] For example, in Netscape Navigator, a typical browser of the World Wide Web, a remote file once accessed is copied to a local disk of a host on which the browser is running. Has a cache function to store.

[0004] As for the World Wide Web,
For example, it is described in detail in the April 1996 issue of the magazine "Open Design" (CQ Publishing Company). Regarding the Netscape cache function, refer to the online document "NETSCAPE NAVI" attached to the software.
GATOR FEATURES FAQ ".

[0005] Japanese Patent Application Laid-Open No. Hei 4-2198 discloses a technique describing a technique related to a network cache system.
No. 39 is published.

[0006]

By the way, in the cache device, when the cache capacity is reached, a method of discarding the contents of the cache, which file in the cache is discarded in order to store a new file. is important. This is because the subsequent access speed may greatly change depending on the method.

In view of the prior art from the viewpoint of discarding the contents of the cache, the above-mentioned Netscape adopts a method of discarding old ones based only on the access time without considering the access frequency. 4
Japanese Patent Application Laid-Open No. 219839 presupposes that a frequently accessed file is cached. These are all based on the cache technology of the main memory in the computer, and do not take into account the characteristics of the remote file obtained via the network. Remote files can vary in size, and generally large remote files take a lot of time to transfer, so even remote files that are infrequently accessed and have not been accessed recently can be cached. If the data is erased, it takes a long time to obtain the data again, and the subsequent access speed may decrease.

Accordingly, an object of the present invention is to provide more efficient caching by controlling the discarding of cache contents when the cache capacity is reached, taking into account the time required for remote file transfer. It is to be.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a remote file caching apparatus for caching a remote file obtained through a network in a local file storage unit for later access, which is expected to be a file management information holding unit. It has a value calculation unit and an access control unit.

The file management information holding unit stores file management information relating to each file stored in the file storage unit, for example, information specifying the host and file storing the file, file size, caching time, The number of hits after caching, the latest update time of the file notified from the file storage source at the time of file acquisition, the last update time, and information on the storage location in the file storage unit are recorded.

The expected value calculation section is based on the individual file management information recorded in the file management information holding section, the time required for file transfer, the number of cache hits per unit time, and the number of file updates per unit time. In consideration of the above, for each individual file, an expected value indicating how much file transfer time can be saved by leaving the file in the file storage unit is calculated.

Such an expected value can be obtained by the following formula: time required for file transfer × (the number of cache hits per unit time−the number of file updates per unit time) (1).

The time required for file transfer in equation (1) can be obtained by the following equation: file size / transfer speed. Here, the size of the file is recorded in the file management information. If the transfer speed is constant regardless of the type of network, one preset value can be used. Of course, it is also possible to use different values preset for each network.

The elapsed time from when the file acquisition request is issued to when the file is actually received may be set as the time required for the file transfer in the equation (1). In this case, the access control unit measures an elapsed time from when the file acquisition request is issued to when the file is actually received, and records the elapsed time as a part of the file management information.

Further, the number of cache hits per unit time in the equation (1) is obtained by dividing the number of cache hits since cache by the elapsed time since the cache, that is, the number of cache hits / ( (Current time-cache time)... (3)

Furthermore, the number of file updates per unit time in equation (1) can be approximately determined from the last two update times. That is, it can be approximated by 1 / (latest update time−immediate update time) (4).

Therefore, the above equation (1) can be approximated as the following equation (5).

[0018]

(Equation 1)

According to the above formula (1) or (5),
The less frequently updated, the longer the time required for transfer, and the more frequently accessed remote files, the greater the expected transfer time. Therefore, compare this value when discarding,
By discarding the file from the smaller one, it is possible to leave a file that saves a large amount of time.

[0020] From the above, the access control unit calculates the expected value calculated by the expected value calculation unit when the free space required for storing the remote file obtained through the network does not exist in the file storage unit. A file having a small value is preferentially erased to secure free space, and the acquired remote file is stored in the file storage unit.

In a preferred embodiment of the present invention, the apparatus further comprises a sorting unit for sorting the file management information in ascending or descending order of the expected value calculated by the expected value calculating unit. Is preferentially erased from the file corresponding to the upper file management information of the sort result, and in the case of descending sort, preferentially erased from the file corresponding to the lower file management information of the sort result.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, one embodiment of a remote file caching apparatus according to the present invention is a network interface unit 1, a file storage unit 2, a file management information holding unit 3, an expected value calculation unit 4, a sort unit 5, It comprises an access control section 6 and a remote file access request means 7. These can be realized by hardware such as a personal computer and a workstation, and control software.

The network interface 1 is a section for exchanging packets with an external network (not shown). Examples of the network to be connected include an ATM network and a LAN using Ethernet. In addition to the mode of connection to a single network, there is a mode of connection to a plurality of different types of networks.

The file storage unit 2 is a storage medium for storing files to be cached, and corresponds to a storage device mainly including a hard disk in a personal computer or a workstation.

The file management information holding unit 3 holds file management information on files cached in the file storage unit 2. At the time of actual mounting, it can be constructed on the same hard disk as the file storage unit 2.

FIG. 2 shows a configuration example of individual file management information held in the file management information holding unit 3. As shown in the figure, the file management information relating to one file includes a host name 21 and a file path 22 which are information for specifying the host and the file that store the file.
, The port name 23 in the TCP / IP connection, the number of cache hits 24, the file size 25, the latest update time 26, the immediately preceding update time 27, the cached time 28, And a file path 29 which is information on the storage location. Here, the latest update time 26 means the latest update time of the file notified at the time of acquisition of the file from the file storage source (time when the file was created at the transfer source). It means the time of the immediately preceding update. When the file is updated at the file storage source after the cache and the latest file content is cached again as described later, the update time 27 recorded immediately before the update time 27 is the last update time 27. Is set. However, when caching is performed for the first time, the latest update time 26
, An appropriate value, for example, the time at which the system started operating is recorded at the immediately preceding update time 27.

FIG. 3 is a diagram showing a specific configuration example of each file management information. In FIG. 3, each line is one file management information. For example, the file management information on the first line includes a host name (www) and a file path (/index.htm) in order from the first field.
l), port name (http) for TCP / IP connection, number of cache hits (1), file size (35)
8), the latest update time of the file (79155554)
0), the time at which the file was updated immediately before the former (0; this 0 indicates a value set because there is no record of the last latest update time 26), and the time at which the file was cached (82928
6336), the file path (\
TEMP\cache\md14. htm).

Referring again to FIG. 1, the expected value calculation unit 4
Indicates the time required for file transfer, the network transfer speed, the number of cache hits per unit time, and the number of file updates per unit time, based on the individual file management information recorded in the file management information holding unit 3. Considering this, an expected value indicating how much file transfer time can be saved by leaving the file in the file storage unit 2 for each individual file is calculated by the above-described equation (1) or its approximate equation. This is a means for calculating by a certain equation (5). Here, when using equation (5), the file size, the number of cache hits, the cache time, the latest update time, and the last update time use the values recorded in the file management information, and the current time is the internal time. Obtained from the timer. The following values can be used as the transfer speed of the network.

(1) Use a constant transfer rate regardless of the type of network. In this case, the value to be used is set in the expected value calculation unit 4 in advance. (2) ATM network, LAN by Ethernet
In an environment where a network is mixed, different transfer rates are used for each network. Also in this case, the value of the transfer speed used for each network is set in the expected value calculation unit 4 in advance. The network to be used can be recognized by the network address of the accessing host.

Next, when the sorting unit 5 is started from the access control unit 6, the file management information holding unit 3
Is transmitted to the expected value calculation unit 4 to calculate the expected value, the file management information is sorted by the calculated expected value in ascending order, and the sorted file management information is stored in the file management information. This is a means for writing back to the unit 3. Note that instead of sorting in ascending order, sorting may be performed in descending order.

The access control section 6 is a section for processing a request for accessing a remote file. The access control unit 6 checks whether or not the latest content of the requested remote file is cached in the file storage unit 2. If cached, the remote control unit 6 notifies the requesting source. The latest file contents are obtained through the network interface unit 1 and notified to the request source, and the file storage unit 2
Caching. And during this caching,
If the free space required to store the remote file acquired this time does not exist in the file storage unit 2, the file with the smaller expected value calculated by the expected value calculator 4 is preferentially erased to secure the free space. . Free space management uses existing technology. For example, the free space variable P initialized to the value 0 at the initial point when no file is stored in the file storage unit 2 is stored in the file management information storage unit 3.
The access control unit 6 subtracts the file size from P each time one file is cached, and adds the file size to P each time one file is deleted. In this method, if the file size to be stored is compared with P, it is checked whether there is enough free space to store the current file.

The remote file access request means 7
This is a means for inputting an external access request when caching a remote file using the apparatus of this embodiment. In this case, together with the access request, information for identifying the host on the network and information for identifying the file are received. For example, the World Wide Web (WW
W), etc. (Uniform Res)
source Locator) is an example of a notation of information that can identify such a host and a file.

FIG. 4 shows an example of the URL. UR in this example
L, the file / test.host of the host whose IP address is 123.45.76.89. txt.
Although an IP address is assumed here, the essential part of the present invention is not limited to TCP / IP.

Next, the operation of the thus configured remote file cache device of the present embodiment will be described.

In the remote file access request means 7,
For example, when a remote file access request specifying a host and a file as shown in FIG. 4 is given,
This is transmitted to the access control unit 6, and the access control unit 6 starts processing.

FIG. 5 is a flowchart showing a processing example of the access control unit 6. When the access control unit 6 detects an access request from the remote file access request means 7 in step S1, first,
It is checked whether or not the corresponding file management information exists in the file management information holding unit 3 (step S2). That is, for example, if the access request of FIG. 4 is given,
The host name 21 and the file path 22 in the file management information composed of the information as shown in FIG. 2 correspond to the IP address 123.45.76.8 of the host shown in FIG.
9, file / test. It is checked whether or not file management information matching txt exists.

If the corresponding file management information does not exist in the file management information holding unit 3, the corresponding file is not cached in the file storage unit 2. A file to be executed is requested (step S3). For example, HTTP (Hyper Te
For example, in the case of a file request through an xt Transfer Protocol (xt Transfer Protocol) connection, an HTTP request shown in FIG. This HTTP request is sent to the file / test. txt.

Next, when a file cannot be normally acquired due to a communication error or the like (N in step S4).
O), this process ends, the process returns to step S1, and waits for the next and subsequent remote file access requests. If the file can be acquired normally (YES in step S4),
MIME (Mul
tipurpose Internet Mail E
(xtensions) header, necessary information such as file size and file update time is obtained (step S).
5). If there is enough free space in the file storage unit 2 to store the transferred file (YES in step S6), the file management information for the file as described in FIGS. The created file is recorded in the file management information holding unit 3 and the transferred file body is recorded in the file storage unit 2 (step S).
7). In the file management information recorded at this time, the number of hits 24 of the cache in FIG. 2 is set to an initial value, the cached time 28 is set to the current time, and the file size 2
5 is set to the size of the file acquired in step S5, and the latest update time 26 is set to the update time acquired in step S5. Also, when the data is transferred for the first time, the immediately preceding update time is not known.
Sets an appropriate value, for example, the time (0) when the system starts operating. Next, the access control unit 6 notifies the request source of the location of the cached file (step S8), and returns to step S1 to wait for the next remote file access request. The location of the cache file may be, for example, a file path or an open file handle.

On the other hand, if there is not enough free space in the file storage unit 2 to store the transferred file (NO in step S6), the access control unit 6
Secures a sufficient free space in the file storage unit 2 to store the file in the following manner.

First, the access control unit 6 starts the sorting unit 5 (step S9). When the sorting unit 5 is activated, it starts processing as shown in FIG. 7, for example. First, all file management information is read from the file management information holding unit 3 (step S21). Next, one of the file management information is passed to the expected value calculation unit 4 to calculate the expected value (step S22).

In the expected value calculation unit 4, the cache hit count 24, FIG.
Based on the file size 25, the latest update time 26, the immediately preceding update time 27, the cached time 28, the current time obtained from the internal timer, and the preset transfer rate, the expected value is calculated by, for example, the above equation (5). The calculated expected value is added to the head of the passed file management information and returned to the sorting unit 5.

The sorting section 5 receives the file management information to which the expected value is added from the expected value calculating section 4 and stores it internally (step 23). Then, it is checked whether or not unprocessed file management information remains (step 24). If so, the processing of steps S22 and S23 is repeated for the unprocessed file management information. When the calculation of the expected values for all the file management information is completed, the internally stored file management information is sorted in ascending order of the expected values (step S25), and the sorted file management information is stored in the file management information. The data is written back to the unit 3 (step S26). Thus, the processing of the sorting unit 5 is completed, and the control is returned to the access control unit 6.

The access control unit 6 includes a sorting unit 5
Is completed, the highest-order file management information of the file management information holding unit 3 in which the sorted file management information is recorded (that is, the one with the smallest expected value) is deleted from the file management information holding unit 3. At the same time, the file body corresponding to the file management information is deleted from the file storage unit 2 (step S10). When the sorting unit 5 sorts in descending order, the file management information is deleted from the lowest order file management information and the corresponding file body. Through the above processing, the free space of the file storage unit 2 is increased by the size of the deleted file body.

Next, the access control unit 6 checks again whether or not enough free space necessary for storing the file to be transferred this time has been secured in the file storage unit 2 (step S11). If so, the process returns to step S10 to delete the file again. The file to be deleted at this time is a file having the next smaller expected value than the previously deleted file. The above process is repeated until a sufficient free space necessary for storing the file is secured. When the necessary and sufficient free space is secured, the file management information for the file to be transferred this time is created and recorded in the file management information holding unit 3 and the file body is recorded in the file storage unit 2 (step S7). ), And notifies the requester of the location of the cache file (step S8).

In step S2, if the file management information of the corresponding file exists in the file management information holding unit 3 (the file is stored in the file storage unit 2).
In the case where the file is cached, the access control unit 6 sends the file to the corresponding host via the network interface unit 1 to check whether the cached file has the latest content. Request information (step S1
2). For example, in the case of an HTTP file information request, an HTTP request as shown in FIG. 8 is transmitted to the server. This HTTP request is sent to the file / test. txt header information is requested.

Next, when the process is not completed normally due to a communication error or the like (NO in step S13), the current process is completed, and the process returns to step S1 to wait for a subsequent remote file access request. If the process is normally completed (YES in step S13), the update time of the file included in the transmitted MIME information is obtained (step S13).
14), the obtained update time is compared with the latest update time 26 shown in FIG. 2 in the file management information of the file confirmed to exist in step S2 (S1).
5).

If the update time transmitted this time is later than the latest update time 26 recorded in the file management information, the file has been updated at the transfer source after the caching, and the file currently cached is I can not use it. Therefore, the access control unit 6 temporarily saves the current file management information inside, deletes the file management information from the file management information holding unit 3, and deletes the corresponding file body from the file storage unit 2, Returning to step S3, the host requests the host to transfer the file as in the case described above. Subsequent processing proceeds in substantially the same manner as in the case described above. However, in the file management information recorded in step S7, at the update time 27 immediately before FIG. The latest update time 26 is set.

On the other hand, in the comparison of the update time in step S15, if the update time of the file transferred this time matches the latest update time 26 recorded in the file management information, the file is cached. Since the file has the latest contents, the file is not transferred, and the number of cache hits in the file management information is 24.
Is incremented by 1 (step S17), the process proceeds to step S8, the position of the file in the file storage unit 2 is returned to the request source, and the process returns to step S1 to wait for the next remote file access request.

In the above embodiment, the time required for the file transfer when obtaining the expected value is calculated using the file size and the preset transfer speed. However, the present invention is not limited to such an example, and the elapsed time from the time when the access control unit 6 requests the server to transfer the file through the network interface unit 1 to the time when the file is completely received is used as the file transfer. It may be used as necessary time. In the case of such an embodiment, “time required for file transfer” is added to the components of the file management information shown in FIG. 2, and the time measured by the access control unit 6 is used as a part of the file management information. Be recorded. Then, the expected value calculation unit 4 calculates the expected value with reference to it.

[0051]

As described above, in the remote file caching apparatus according to the present invention, by taking into account the time required for file transfer, how much file transfer time can be saved by caching afterwards. , The file in the cache is discarded using the expected value indicating that the remote file is cached more efficiently than when the file is discarded only based on the last access time or the number of cache hits.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a remote file cache device according to the present invention.

FIG. 2 is a diagram illustrating a configuration example of individual file management information held in a file management information holding unit.

FIG. 3 is a diagram illustrating a specific configuration example of individual file management information held in a file management information holding unit.

FIG. 4 is a diagram showing an example of a host specification in an IP address format specified by an access request and a file specification thereon.

FIG. 5 is a flowchart illustrating a processing example of an access control unit.

FIG. 6 is a diagram illustrating an example of a command for requesting a file through an HTTP connection.

FIG. 7 is a flowchart illustrating a processing example of a sorting unit.

FIG. 8 is a diagram illustrating an example of a command for requesting only information about a file through an HTTP connection.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Network interface part 2 ... File storage part 3 ... File management information holding part 4 ... Expected value calculation part 5 ... Sorting part 6 ... Access control part 7 ... Remote file access request means

Claims (7)

(57) [Claims]
1. A remote file cache device for caching a remote file obtained through a network in a local file storage unit for later access, wherein file management for individual files stored in the file storage unit is performed. A file management information holding unit for recording information, and referring to the file management information stored in the file management information holding unit, the time required for file transfer, the number of cache hits per unit time, and the number of files per unit time. An expected value calculating unit for calculating an expected value indicating how much file transfer time can be saved by keeping the file in the file storage unit for each file in consideration of the number of updates; To store remote files obtained through If there is no free space required in the file storage unit, the expected value calculated by the expected value calculation unit is preferentially erased from the smaller files to secure free space,
An access control unit for storing the acquired remote file in the file storage unit.
2. The method according to claim 1, wherein the expected value calculation unit includes:
2. The remote file cache device according to claim 1, wherein a value given by (time required for file transfer) ((number of cache hits per unit time-number of file updates per unit time)) is set as the expected value.
3. A sort unit for sorting the file management information in ascending or descending order of the expected value calculated by the expected value calculating unit, wherein the access control unit, in the case of the ascending sort, a higher-ranking file of the sort result 3. The remote control according to claim 2, wherein a file corresponding to the management information is preferentially deleted, and in the case of descending sort, a file corresponding to the file management information lower in the sorting result is preferentially deleted. File caching device.
4. The expected value calculation unit calculates a time required for file transfer by using a file size / transfer speed using a file size recorded in file management information and a preset transfer speed. 4. The remote file cache device according to claim 3, having a configuration.
5. The apparatus according to claim 1, wherein the expected value calculation unit uses a file transfer time measured when each file is acquired and recorded in file management information as a time required for file transfer. 4. The remote file cache device according to claim 3, wherein:
6. The expected value calculation unit uses the number of cache hits per unit time as the number of cache hits and the cache time recorded in the file management information, and calculates the number of cache hits / (current time−cache time). The remote file cache device according to claim 4, wherein the remote file cache device has a configuration that approximates the time.
7. The expected value calculation unit calculates the number of file updates per unit time using the latest update time recorded in the file management information and the immediately preceding update time, by using 1 / (the latest update time−the immediately preceding update time). The remote file cache device according to claim 4, wherein the remote file cache device has a configuration approximated by (update time).
JP8217972A 1996-07-31 1996-07-31 Remote file cache device Expired - Lifetime JP2976896B2 (en)

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Cited By (1)

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WO2004109552A2 (en) 2003-06-03 2004-12-16 Access Co., Ltd. Method for browsing contents using page storing file

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JP3844588B2 (en) 1998-03-05 2006-11-15 富士通株式会社 Information management system, local computer, and computer-readable recording medium recording information acquisition program
JP3424907B2 (en) 1998-07-02 2003-07-07 日本電気株式会社 Network content cache device
CN1328892C (en) * 1999-11-01 2007-07-25 松下电器产业株式会社 Method and apparatus for information transmission
JP4505977B2 (en) * 2000-11-10 2010-07-21 ソニー株式会社 Data storage device and method, and recording medium
JP2008269657A (en) * 2008-08-11 2008-11-06 Murata Mach Ltd Content data providing device and network system
KR101139754B1 (en) * 2009-07-23 2012-04-26 주식회사 아라기술 Method, system and computer-readable recording medium for providing information to dispersed users using data cache based on mirroring
JP5567967B2 (en) * 2010-09-30 2014-08-06 インターナショナル・ビジネス・マシーンズ・コーポレーションInternational Business Machines Corporation Cache control method, system and program in database
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WO2004109552A2 (en) 2003-06-03 2004-12-16 Access Co., Ltd. Method for browsing contents using page storing file

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