JP2008146516A - Data read-ahead processing method for recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quicken an access to a positionally discontinuous data arranged on a recorder. <P>SOLUTION: A retrieval system comprises a controller for controlling retrieval processing, and the recorder mounted with a read-ahead command for storing an assignment data in a cache memory built in the recorder. The controller indicates data read-ahead required in the next to the recorder, using the read-ahead command, during processing of the data, the recorder reads out the assigned data from a recording medium, to be stored into the cache memory, and the data is thereby read quickly from the recorder built in the recorder, without accessing the recording medium, when the controller reads the next data from the recorder. A hit rate of the cache memory is also enhanced to quicken the reading, by adding a priority and a protection flag to an area indicated and read by the read-ahead command to control efficiently the cache memory. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a processing program for storing data on a recording device and reading the data, and by causing the data to be read in advance on the internal cache memory of the recording device so that the time for reading data from the recording device can be shortened. And the recording apparatus.

  In a computer system, generally, a time required for reading and writing data between a recording device and a memory inside a computer is much longer than a time required for data processing inside the computer. In a computer system that continuously reads related data, the processing performance of the system can be improved by improving the efficiency of the data reading process.

  As a method for this, a method for efficiently using the cache memory in the recording device and shortening the response time to the read request, and a process of displaying or searching the read data in the computer system are performed. There is a method of reading data required later from the recording device in advance during the idle time.

  FIG. 1 is a block diagram showing the outline of this computer system, which is composed of a control device 10 that accepts a user's search instruction and controls the search, processing, and output of data, and a recording device 11 that stores data. The The control device 10 includes a data processing unit 101 that controls data operations such as data search and processing, and data input / output processing to the recording device, an input unit 102 that receives a search instruction from a user, and a data processing unit 101. An output unit 103 that outputs the generated information to the user, and a memory 104 that temporarily stores data read from the recording device 11, the recording device 11 includes a recording medium 111 that actually stores data, A cache memory 112 that holds data read from the recording medium 111 and an input / output control unit 113 that controls reading from the recording medium 111 and storage of data in the cache memory 112 are configured.

  FIG. 2 shows a data reading process in the recording apparatus 11 having a general cache function. The input / output control unit 113 confirms whether the designated data is stored in the cache memory 112 (step 201), and if not, reads it from the recording medium 111 (step 202) and holds it on the cache memory 112 (step 201). Step 203). This data is transferred to the requesting control system (step 204), and the reading process is completed (step 205). Here, the input / output control unit 113 uses not only the requested data but also the fact that the data that is positionally continuous with the last accessed data on the recording medium 111 is likely to be accessed in the near future. Data that is consecutive in position is also read from the recording medium 111 in advance (step 202) and stored in the cache memory 112 (step 203). Therefore, in the subsequent read request, when the acquisition target data is held in the cache memory 112, it is possible to respond to the read request at high speed without accessing the recording medium 111 (Steps 201, 204, and 205). For example, in a document management system or the like, a series of document data is physically continuously stored on the recording medium 111 to improve search performance by using the prefetching effect of the recording device 11.

  In a car navigation system, it is necessary to read out map data of a destination in accordance with the movement of the host vehicle in a route traveling with a destination set and display a map image without delay. However, since the map data having a two-dimensional extent cannot be continuously arranged on the recording medium 111 according to a route that cannot be predicted in advance, the prefetch effect of the recording device 11 cannot be used. Therefore, the control device 10 uses the idle time while the data processing unit 101 and the output unit 103 process and display the read data, and records in advance a data that may be required thereafter. 11 and stored in the memory 104. Since this process involves reading from the recording medium 111 (step 202), it takes a long time. However, when the data processing unit 101 needs the target data, access to the recording apparatus 11 becomes unnecessary, and the data can be quickly stored. Processing and display can be performed.

  In addition, there exists the following patent document 1 as a well-known technical document relevant to this invention.

JP 2003-263348 A

In a system that reads a plurality of related data from a recording device that does not have continuity of storage positions, as in the case of a car navigation system, the conventional prefetch cache function of the recording device is effective. I can't expect it. Therefore, a method of reading data on the recording device in advance to the memory on the control device side is used, but this method has the following problems.
(1) In the process of reading data that will be required in the future from the recording device in advance, there is a high possibility that the target data does not exist in the cache memory of the recording device and is read from the recording medium, and it is necessary to wait for its completion Therefore, sufficient free time is required for processing of the control device.
(2) Since the prefetched data from the recording device is held in the memory area of the control device until it is used, a part of the memory area is occupied during that time.

  An object of the present invention is to provide a data prefetching processing method that can efficiently perform prefetching of data having no continuity at storage positions after solving the above-mentioned problems.

  In order to achieve the above object, the data prefetch processing method of the present invention is a processing program that performs a read process of user request data, and a recording device including an internal cache mechanism, and a prefetch request from the processing program. And a means for reading prefetch request data from a recording medium into a cache memory inside the recording apparatus, and the processing program is a processing program for performing a read process of the request data. Means for receiving a prefetch request for a plurality of necessary data, means for instructing a prefetch to the recording device based on the accepted request, and means for processing the read data in parallel with the prefetch processing performed by the recording device A recording apparatus that pre-reads request data in accordance with a pre-read instruction from a processing program. When the pre-reading instruction is received, the reading process from the recording medium is started, and at the same time, a request acceptance completion report to the request source is sent, and the requested data is not returned to the request source, but from the recording medium. There are provided means for only reading to the internal cache memory of the recording apparatus and means for transferring the data already read on the cache memory to the request source in accordance with a read instruction from the processing program.

  According to the data prefetching processing method of the present invention, the following effects are obtained.

  The storage location on the recording medium is not continuous, as in the case where the data is managed separately in the index part and the data part, or the data is managed in the chain structure. In a system that stores data in an arrangement that has a low effect, the prefetch function by the recording device can be used.

  In the read processing of a plurality of data where the storage positions on the recording medium are not continuous, the processing time in the control device is not consumed by performing the pre-read processing in the recording device in parallel with the data processing in the control device. Pre-read processing is realized, and high-speed data access is possible.

  In the read processing of a plurality of data where the storage position on the recording medium has no continuity, prefetch processing is realized without using the memory area of the control device by holding the prefetch data in the cache memory inside the recording device, High-speed data access is possible.

  In the recording device, when data is read from the recording medium and stored in the cache memory according to the prefetch request instructed by the user, the data is read in the order specified by the user by optimally rearranging the reading order from the recording medium. Reading from the recording medium is completed faster than the method to be performed.

  In the recording device, the data read by the prefetch request instructed by the user is given a priority and is held longer than the other data area in the cache memory, or is held in the cache memory until it is actually read, The cache hit rate can be improved as compared with the normal cache management method.

  Hereinafter, an embodiment of a search system to which the present invention is applied will be described.

  FIG. 3 is a system configuration diagram showing an example of an embodiment of the present invention. This search system is composed of a recording device 31 that stores map data and a control device 30 that performs search and display processing for this data. This is a car navigation system. The control device 30 includes a data processing unit 301 that performs processing such as data search and processing, an input unit 302 that acquires user operation and GPS (Global Positioning System) position information, and an output that displays a map image. And a memory 304 that temporarily stores data.

  The recording device 31 includes a recording medium 311 storing map data, a cache memory 312, an input / output control unit 313, and a prefetch control unit 314. The interface between the control device 30 and the recording device 31 uses a recording device interface circuit if necessary. The input / output control unit 313 receives a general access command including a read command for reading data from the recording medium 311 and controls data input / output processing between the recording medium 311 and the cache memory 312. The prefetch control unit 314 receives a prefetch command for reading data from the recording medium 311 and storing the data in the cache memory 312, interacts with the input / output control unit 313, and performs data input / output processing between the recording medium 311 and the cache memory 312. To control.

  FIG. 4 shows the physical arrangement of map data stored in the recording medium 311 and the semantic relevance. The map data is managed by being divided into an index part 43 and a data part 44 and stored in the recording medium 311. The data unit 44 is composed of map section data obtained by dividing the map data into fixed size units. The map section data 421 to 427 representing the vicinity of the current position 41 semantically represent adjacent map information, but the physical arrangement on the recording medium 311 is not necessarily continuous.

  FIG. 5 shows a flow of search processing in the control device 30 of this system, and FIG. 6 shows a flow of data prefetch processing when the prefetch control unit 314 receives a prefetch command. Data read processing when the input / output control unit 313 receives a read command is the same as that in FIG.

  First, the data processing unit 301 searches for map information corresponding to the current position 41, reads the corresponding map section data 424 from the recording device 31, and stores it in the memory 304 (step 501). A map image is generated based on this data, and the output unit 303 performs display processing.

  The data processing unit 301 determines a map image to be read next in accordance with the input information of the input unit 302 (step 502). From the current position and the route information of the traveling direction, the next necessary data is predicted to be map sections 422 and 425. Here, the map section 425 is stored in the cache memory 312 by the pre-reading of the recording device 31 because the stored map section 424 and the storage position on the recording medium 311 are continuous. Since the storage position of the section 422 is remote, the possibility is low.

  The data processing unit 301 issues the prefetch command by designating the data of the map sections 422 and 425 to the recording device 31 while displaying the information within the range of the map section data 421 near the current position. (Step 503). As soon as the prefetch control unit 314 of the recording apparatus accepts the command, it notifies the request source of the completion of acceptance (step 601). Therefore, immediately after issuing the command, the data processing unit 301 can use the data in the vicinity of the current position stored in the memory 304 and continue the image generation and display processing (step 504).

  In parallel with the data processing unit 301 continuing the processing, the prefetch control unit 314 of the recording apparatus continues the prefetch command processing. It is confirmed whether the designated data is stored in the cache memory 312 (step 602). If not, the target data is read from the recording medium 311 (step 603) and stored in the cache memory 312 (step 604). At this time, only reading to the cache memory 312 is performed, and transfer to the request source is not performed.

  Here, for the pre-read commands issued continuously, the pre-read control unit 314 rearranges the requests in accordance with the physical arrangement of the requested data, optimizes access to the recording medium 311, and then performs actual reading. Process. The command issuer need not be aware of the arrangement of the target data and the command issue order when issuing the prefetch command.

  When the current position 41 changes and the data processing unit 301 needs the data of the map sections 422 and 225, the data processing unit 301 issues a read command to the recording device 31 and reads the target data from the recording device 31. And stored in the memory 304 (step 505). At this point, the pre-read command issued in advance has been processed, and the target data is stored in the cache memory 312 of the recording apparatus. Therefore, the input / output control unit 313 that has received the read command performs only data transfer from the cache memory 312 to the memory 304 of the control device without accessing the recording medium 311, and the command is completed in a short time. Thereby, the data processing unit 301 and the output unit 303 can display the map image accompanying the movement of the current position 41 without delay.

  In this way, by giving an instruction to store the designated data in the cache memory 312 to the recording device 31 in advance, the data processing in the control device 30 and the reading processing from the recording medium 311 in the recording device 31 are parallelized. Thus, it is possible to speed up access to data stored in a distributed manner on the recording medium 311. This read-ahead processing method is applicable not only to the data structure of index management but also to various systems that access data that is less effective with a simple read-ahead cache, such as chain management data, in which it is difficult to arrange read data linearly. be able to.

  FIG. 7 shows a process of storing data in the cache memory 312 built in the recording device 31 in the read process and the prefetch process. This is a process corresponding to step 203 of the read process and step 604 of the prefetch process.

  First, it is determined whether there is a free area in the cache memory 312 (step 701). If there is a free area, it is set as a data storage area (step 703). If there is no free space, the data with the lowest priority among the stored data is selected as the discard target, and the area is set as a new data storage area (step 702). Data is stored in the storage area on the cache memory 312 selected in this way (step 704).

  In general recording devices, priorities are set for stored data based on an algorithm that gives priority to data areas that are read frequently or data that has a new storage time, and discards low priority data when the cache is full. Process. In the present invention, the data area read using the prefetch command is set to a higher priority than the data on the other caches (steps 705 and 706), so that the discard target data is selected (step 702). ), Data read by the pre-read command is preferentially left over other data. As a result, it is possible to increase the probability that the data specified by the prefetch command is stored in the cache memory 312 when a normal read request is received.

  Also, a protection flag is set in the data area read using the prefetch command (step 707). When selecting the data to be discarded when the cache memory 312 is full (step 702), the pre-read command is issued (step 503) by not discarding the area where the protection flag is set. The data area can be prevented from being discarded from the cache memory 312 until the actual data read time (step 505). This protection flag is canceled when the corresponding data area is actually read from the cache. If the data with the protection flag set continues to be stored in the cache memory 312 without being read, when the ratio exceeds the threshold, the one with the lowest priority is selected and the setting is canceled.

  The management of the cache memory 312 based on the priority and the management of the cache memory 312 based on the protection flag can be applied individually or in combination.

  As described above, by improving the management method of the data area stored in the built-in cache memory 312 of the recording device 31, the use efficiency of the cache memory 312 can be improved by using the prefetch command of the present invention.

It is a schematic block diagram of the conventional search system. It is a flowchart which shows the data reading process in a recording device. 1 is a system configuration diagram showing an embodiment of the present invention. It is explanatory drawing of the specific example of arrangement | positioning of the data on a recording medium. It is a flowchart which shows the data processing of a search system. It is a flowchart which shows the data prefetch process in a recording device. It is a flowchart which shows the cache storage process in a recording device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 30 ... Control apparatus, 301 ... Data processing part, 302 ... Input part, 303 ... Output part, 304 ... Memory, 31 ... Recording apparatus, 311 ... Recording medium 311 ... Cache memory, 313 ... Input / output control part, 314 ... Prefetch control Department.

Claims (4)

  A recording apparatus having a processing program for reading user request data and an internal cache mechanism, a means for receiving a prefetch request from the processing program, and a cache memory in the recording apparatus for prefetch request data from the recording medium A data pre-reading processing method characterized by comprising:   In the data prefetching processing method according to claim 1, in the recording device, means for accepting a prefetch request for a plurality of data requiring prefetching instructed by a user, means for instructing a prefetch to the recording device based on the accepted request, A data prefetch processing program comprising means for processing read data in parallel with the prefetch processing.   In the data prefetching processing method according to claim 1, means for receiving a prefetching instruction from the processing program, and starting a reading process from the recording medium when the prefetching instruction is accepted, and simultaneously performing a request acceptance completion report to the request source; The requested data is not returned to the request source, but only means for reading from the recording medium to the internal cache memory of the recording apparatus, and the data already read on the cache memory by the read instruction from the processing program to the request source A recording apparatus comprising a transfer unit.   4. The recording apparatus according to claim 3, wherein means for rearranging the execution order of the requested data in order to optimize a process for reading the requested data from the recording medium, and a cache that is full from the recording medium in the recording apparatus. When reading and storing data in the memory, a means for preferentially leaving the data stored by the pre-read designation among the stored data, and for the data read into the internal cache memory of the recording device A recording apparatus control system comprising: means for suppressing normal cache prefetch control in an actual read request.

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