JP2018173802A - Storage system, data sorting method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a storage system capable of improving reading performance, a data sorting method, and a program.SOLUTION: The data generated by dividing one parent data into a plurality of data is called child data. A storage system: sequentially stores child data in a file of a storage device with parent data different to each other as a division source; stores the position read lastly from the file by file read processing in the storage device according to the execution of file read processing; and subjects the child file stored after the position readout to sort processing for sorting child data in the file.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a storage system, and more particularly to a re-store process performed in the storage system.

  For example, some storage systems, such as backup storage, execute a process of rearranging or re-storing the stored stream data so as to be continuously arranged in order to improve read performance.

  When the load on the storage system is high, it takes time to complete the sort process. For this reason, if the storage system continues to be heavily loaded, a large amount of sort processing may remain. In such a case, if a read process is executed in the storage system, a large amount of unprocessed data exists in the storage area of the storage system, so the read process takes longer than usual.

  Patent document 1 is given as a thing relevant to this invention. Patent Document 1 discloses that data having the same stream ID is continuously arranged when the stream data is written from the buffer memory to the data storage device in order to improve the reading performance of the data written in a plurality of streams.

  The data exceeding the buffer memory is fragmented and becomes, for example, a data arrangement state as shown in FIG. F1 to F12 represent data storage areas, in which data written by the user is stored in order from the top. ST1 to ST3 are stream IDs that are assigned to distinguish a plurality of pieces of backup target data. In FIG. 9, each represents different data written by the user. From this state, in order to further improve the data reading performance, the process of sorting data having the same stream ID is referred to as a re-storing process.

Japanese Patent No. 5413948

  Generally, the re-storing process is performed when system resources are available. When there is a load from the outside, it waits for execution of the re-storing process. When the system load is high, the read process may be executed before the re-store process.

In the storage system storing data as shown in FIG. 9, it is assumed that a read process occurs as shown in FIG. In the example of FIG. 10, the re-storing process is executed from the head of each of the data storage folders F1 to F12, and the process up to POS _{P is} completed. On the other hand, the reading process proceeds to POS _R. Data is stored up to POS _E and is waiting for a re-store process.

In this situation, POS _R precedes POS _P. From this situation, it is not normal for POS _P to overtake POS _R and reverse the progress. For this reason, subsequent read processing is always performed on data that has not yet been re-stored. As a result, the read performance of the storage system is adversely affected.

  The present invention has been made in view of such a situation, and a problem to be solved by the present invention is to provide a storage system, a data sort method, and a program capable of improving read performance. .

  In order to solve the above-mentioned problems, the present invention, as one aspect thereof, in the case where data generated by dividing one parent data into a plurality of pieces is called child data, the child data having different parent data as a division source is ordered. Means for storing in a file in the storage device, means for storing in the storage device the position read last from the file by the read processing in response to execution of the file read processing, and storing the child data in the file There is provided a storage system comprising means for performing a sorting process for sorting on the child files stored after the position.

  Further, according to another aspect of the present invention, when data generated by dividing one parent data into a plurality of pieces is called child data, child data having different parent data as a division source is sequentially stored in the storage device. A step of storing in a file; a step of storing in a storage device a position read last from the file by the reading process in accordance with execution of the reading process of the file; a sorting process for sorting the child data in the file; A method for sorting data in a file stored in a storage system, including the step of performing the process on the child file stored after the location.

  Further, according to another aspect of the present invention, when data generated by dividing one parent data into a plurality of pieces is called child data, child data having different parent data as a division source is sequentially stored in the storage device. Means for storing in a file; means for storing in a storage device the position read last from the file by the read process in accordance with execution of the file read process; and a sort process for sorting the child data in the file A program for causing a computer to realize means for the child file stored after the location is provided.

  According to the present invention, it is possible to improve the read performance of the storage system.

1 is a block diagram of a storage system 1 according to a first embodiment of the present invention. It is a figure for demonstrating the relationship between parent data D1, D2, D3 and each child data. 4 is a diagram for explaining an example of initial arrangement of child data in a file F stored in a storage device 31 of the storage system 1. FIG. In the storage system 1 is a diagram for describing re-storing process (sorting) to be executed after reading to the position POS _R reads the file F. 6 is a diagram for explaining an example of data arrangement in a file F after executing a re-storing process in the storage system 1. FIG. It is a block diagram of the storage system 10 which concerns on 2nd Embodiment of this invention. 4 is a flowchart for explaining the operation of the storage system 10. The value of the termination / restart position POS _P of restoring process, after updating the value of the position POS _R of the read pre pointer is a diagram for explaining the progress of the reading process and re-storing process. It is a figure which shows the example of a data arrangement | positioning in a memory | storage device when three stream data ST1, ST2, ST3 are stored in the storage system of patent document 1. FIG. FIG. 10 is a diagram for explaining the progress of a read process and a restore process when the storage system of Patent Document 1 is in a state where data is stored in the arrangement of FIG. 9.

[First Embodiment]
The storage system 1 according to the first embodiment of the present invention will be described. Referring to FIG. 1, the storage system 1 includes a storage device 31, a divided storage control unit 25, a read information storage unit 33, and a storage location management unit 26.

  The distributed storage control unit 25 writes the data input to the storage system 1 in the storage device 31. At this time, the distributed storage control unit 25 divides one data into a plurality of data and writes the data.

  The relationship between the data before and after the division will be described. Here, data before division is called parent data, and data after division is called child data. Referring to FIG. 2, the parent data D1 includes child data d1-1, d1-2,..., D1-L (L is a natural number). Each child data is obtained by dividing the parent data D1 by a predetermined size in the input order. Similarly, the parent data D2 includes child data d2-1, d2-2,..., D2-M (M is a natural number), and the parent data D3 includes child data d3-1, d3-2,. N is a natural number).

  Consider a case where a plurality of data is input to the storage system 1 in parallel. The distributed storage control unit 25 writes in the storage device 31 according to the input order. At this time, the data is written in the storage device 31 according to the input order in the child data unit, not in the input order in the parent data unit. Immediately after the writing, the child data is arranged as shown in FIG. 3, for example. As shown in FIG. 3, the distributed storage control unit 25 writes the file F in the file F according to the input order of the child data from the head to the end of the file F.

Now, the reading process is generated for the file F of FIG. 3, as shown in FIG. 4, and reads the file F from the head to position POS _R in order. In this case, the storage position management unit 26, in response to execution of the file reading process, the reading process is last read stored in the position POS _R reads completion information storage unit 33 from the file.

  At this time, the distributed storage control unit 25 performs a sorting process for sorting the child data in the file, that is, a re-storing process on the child file stored after the position stored in the read information storage unit 33. . The re-storing process is for improving the reading speed of the file F by arranging the arrangement of the child files in the file F.

An example of the data arrangement in the file F after the re-storage process is shown in FIG. In this example, position POS _R after, firstly, each child data are arranged together by dividing original parent data. Child data d1-9 and d1-10 with parent data D1 as the division source are stored in succession, and then child data d2-6 and d2-7 with parent data D2 as the division source are stored in succession. Finally, child data d3-5, d3-6,..., D3-9 having the parent data D3 as a division source are successively stored. Further, the child data having the same parent data as the division source is arranged in an order corresponding to the input order.

Thus storage, when the reading process has occurred, storing the last read position POS _R, by executing the re-storing process to the data stored at that location after, the reading position POS _R after It is possible to speed up the reading process of the data that has been read.

[Second Embodiment]
A storage system 10 according to the second embodiment of the present invention will be described. Referring to FIG. 6, the storage system 10 includes a data processing device 20 and a data storage device 30. The storage system 10 is a system constituted by a single computer or a plurality of computers. The data processing device 20 and the data storage device 30 may be configured by a single computer, or the data processing device 20 and the data storage device 30 may be configured as separate computers. Furthermore, each of the data processing device 20 and the data storage device 30 may be configured by a plurality of computers.

  The storage system 10 is a content address storage system. In the content address storage system, data is divided and made redundant, distributed and stored in a plurality of storage devices. In the content address storage system, the storage location where the data is stored is specified by a unique content address set according to the content of the stored data.

  The data processing device 20 controls data storage and reading operations with respect to the data storage device 30. The data storage device 30 is a device that includes a storage medium that stores data. When the data processing device 20 and the data storage device 30 are each configured as a single computer, it is conceivable that the data processing device 20 and the data storage device 30 are each configured by, for example, a server computer device.

  The data processing device 20 includes a stream ID (Identifier) assigning unit 21, a block generation unit 22, a duplication check unit 23, a fragment generation unit 24, a distributed storage control unit 25, and a storage location management unit 26. The data storage device 30 includes a plurality of storage devices 31, a storage position information storage unit 32, and a read information storage unit 33.

  When receiving the input of the target data A that is a group of data, the stream ID assigning unit 21 assigns a stream ID that is identification information for distinguishing the target data A. For example, stream ID = ST1 is assigned to the target data A, and stream ID = ST2 is assigned to the target data B (not shown).

  When receiving the input of the target data A, the block generation unit 22 divides the target data A into block data D having a predetermined capacity (for example, 64 KB).

  Further, the block generation unit 22 calculates a unique hash value H (content identification information) representing the content of the block data D based on the data content of the block data D. For example, the hash value H is calculated from the data content of the block data D using a preset hash function.

  Furthermore, the block generation unit 22 inherits and assigns the stream ID assigned to the target data A to each block data D generated by dividing the target data A.

  The duplication check unit 23 uses the hash value H of the block data D of the target data A to check whether the block data D is already stored in the storage device 31.

  Specifically, first, the block data D that has already been stored has its hash value H and a content address CA representing the storage position associated with each other and registered in an MFI (Main Fragment Index) file. Therefore, when the hash value H of the block data D calculated before storage is present in the MFI file, the duplication check unit 23 can determine that the block data D having the same content has already been stored.

  In this case, the content address CA associated with the hash value H in the MFI that matches the hash value H of the block data D before storage is acquired from the MFI file. Then, this content address CA is returned as the content address CA of the block data D relating to the storage request.

  As a result, the already stored data referred to by the content address CA is used as the block data D requested to be stored, and the block data D related to the storage request need not be stored.

  The fragment generation unit 24 compresses the block data D determined not to be stored yet by the duplication check unit 23 and divides it into a plurality of fragment data having a predetermined capacity. For example, the data is divided into nine fragment data corresponding to the codes D1 to D9.

  In addition, the fragment generation unit 24 generates redundant data so that the original block data can be restored even if some of the divided fragment data is missing. The fragment generation unit 24 adds the generated redundant data to the fragment data to generate one data set.

  For example, the fragment generation unit 24 adds three redundant data corresponding to the codes D10 to D12 to the nine fragment data D1 to D9 to generate one data set. That is, the fragment generation unit 24 generates a data set corresponding to the block data D that the duplication check unit 23 determines to be unstored. Hereinafter, both of data generated by compressing and dividing block data D such as fragment data D1 to D9 and data generated for realizing redundancy such as redundant data D10 to D12 are generically referred to. Sometimes called fragment data. The fragment data D1 to D12 are preferably created so as to have the same capacity.

  Further, the fragment generation unit 24 applies to all the generated fragment data D1 to D12 the block data D that is the original of the fragment data, that is, the stream ID assigned to the block data D restored from the fragment data D1 to D12. Are given respectively.

  The distributed storage control unit 25 stores each fragment data constituting the data set generated by the fragment generation unit 24 in a distributed manner in each storage area formed in the storage device 31.

  For example, the storage system 10 provides 12 storage devices as the plurality of storage devices 31 and prepares a data storage file F for each storage device. At this time, the storage system 10 has 12 data storage files F1 to F12 as data storage areas. The distributed storage control unit 25 stores one of the fragment data D1 to D12 in each of these twelve data storage files F1 to F12. That is, the distributed storage control unit 25 stores the fragment data D1 in the data storage file F1 of one storage device 31, and stores the fragment data D2 in the data storage file F2 of another storage device 31. A plurality of fragment data constituting the same data set are stored in data storage files of different storage devices.

  Further, when storing the fragment data of the same data set in different storage devices 31, the distributed storage control unit 25 stores them at the same position in each data storage file.

  For example, as in the above-described example, the storage system 10 includes 12 storage devices 31, each storage device 31 has data storage files F1 to F12, and a data set corresponding to a certain block data D includes 12 data sets It is assumed that the data consists of fragment data D1 to D12. When the distributed storage control unit 25 stores the fragment data D1 in the data storage file F1, it is assumed that it is stored in the U bit (U is a natural number) from the head of the data storage file F1. At this time, the distributed storage control unit 25 also stores the U-bit from the top of the data storage file F2 when storing the fragment data D2 in the data storage file F2. The same applies to the storage of the other fragment data D3 to D12.

  When storing a plurality of target data simultaneously in the storage system 10, the distributed storage control unit 25 may store data sets derived from different target data alternately in the data storage file. For example, it is assumed that the storage system 10 receives input of three target data at the same time. It is assumed that the stream ID assigning unit 21 assigns ST1, ST2, and ST3 as stream IDs in order to these three target data. At this time, the data storage folders F1 to F12 store fragment data as shown in FIG. 7, for example.

  In FIG. 7, fragment data derived from the same target data are given the same shading. In other words, the fragment data of stream ID = ST1 is shaded with diagonal lines from the upper right to the lower left. The fragment data of stream ID = ST2 is given a grid-like shade. The fragment data of stream ID = ST3 is hatched in an oblique lattice pattern.

  Further, the distributed storage control unit 25 distinguishes the fragment data D1 to D12 for each stream ID and temporarily stores them in different buffer memories before storing them in the data storage files F1 to F12. Thereafter, the fragment data D1 to D12 in the buffer memory are stored in the data storage files F1 to F12.

  In addition, as described above, the distributed storage control unit 25 not only stores fragment data in the data storage file but also continuously stores fragment data with the same stream ID for already stored fragment data. It also has a function of changing the storage position afterwards so that it is arranged. For example, when the resources of the storage system 10 itself are vacant over a predetermined value, the storage positions of the fragment data stored in the data storage files F1 to F12 are moved so that the same stream IDs continue. Specifically, the storage position of all fragment data stored in the same storage position (horizontal row) of each data storage file F1 to F12 is changed for each data set 40 composed of the fragment data. can do. Thereby, it is possible to change from a state in which data sets having different stream IDs are alternately stored to a state in which data having the same stream ID are continuously stored.

  In addition, the distributed storage control unit 25 gives the same identification information (WriteRecordSeqNum) to each fragment data D1 to D12 constituting the data set 40 in order to identify that the same data set 40 is constituted. And stored in the data storage files F1 to F12, respectively. Then, the distributed storage control unit 25 checks the identification information at an arbitrary timing such as when the resources of the storage system 10 are available. Thereby, it can be checked whether each fragment data which comprises the same data set 40 is stored in the same storage position in each data storage file F1-F12. Therefore, the distributed storage control unit 25 determines that each fragment data stored in the same storage position in each data storage file F1 to F12 does not include the same identification information (WriteRecordSeqNum). The storage position is corrected so that the data is stored in the same storage position, and the data is stored again.

  Further, the distributed storage control unit 25 performs a process of reading data currently stored in the storage device 31.

  As described above, the storage location management unit 26 stores the fragment data D1 to D12 stored in the storage device 31, that is, the content address indicating the storage location of the block data D restored by the fragment data D1 to D12. Generate and manage CA. Specifically, a part of the hash value H (short hash) calculated based on the contents of the stored block data D (for example, the top 8B (bytes) of the hash value H), information indicating the logical storage position, Are combined to generate a content address CA. Then, the content address CA is returned to the file system in the storage system 10. Then, the file system manages the identification information such as the file name of the target data in association with the content address CA.

  Further, the storage location management unit 26 associates the content address CA of the block data D with the hash value H of the block data D, and each storage node 10B manages it with the MFI file. As described above, the content address CA is stored in the storage position information storage unit 32 in association with information for specifying the file, the hash value H, and the like.

  Furthermore, the storage location management unit 26 performs control to read the target data stored as described above. For example, when a read request is made by designating a specific file to the storage system 10, first, based on the file system, a short hash and a logical position that are part of a hash value corresponding to the file related to the read request A content address CA consisting of the above information is designated. Then, the storage location management unit 26 checks whether or not the content address CA is registered in the MFI file. If it is not registered, the requested data is not stored and an error is returned.

  On the other hand, if the content address CA related to the read request is registered, the storage location specified by the content address CA is specified, and each fragment data stored in the specified storage location is read out. As read data. At this time, if the data storage files F1 to F12 in which each fragment is stored and the storage position of one fragment data in the data storage file are known, the storage position of other fragment data is specified from the same storage position. be able to.

  Then, the storage location management unit 26 restores the block data D from each fragment data read in response to the read request. Furthermore, the storage location management unit 25 concatenates a plurality of restored block data D, restores them to a group of data such as file A, and returns them to the reading source.

  The data storage device 30 includes a plurality of storage devices 31, a storage position information storage unit 32, and a read information storage unit 33.

  Each storage device 31 is a storage device that stores data to be stored in the storage system 10. The storage device used as the storage device 31 is, for example, a hard disk drive or an SSD (Solid State Drive).

  The storage position information storage unit 32 is a storage device that stores the storage position of the stored data. A storage device used as the storage location information storage unit 32 is, for example, a hard disk drive or an SSD.

The read information storage unit 33 stores a read pointer POS _R that is position information indicating a position where reading of data by the reading process is interrupted. Further, the read information storage unit 33 stores a position where the re-storing process is completed, that is, a position POS _{P at} which the next re-storing process is started.

  Next, the operation of the storage system 10 will be described. The storage system 10 holds position information indicating the position where the reading process has already been completed among the data stored in the storage device 31. Based on this position information, among the data that has not been re-stored, the priority of the re-store process is lowered for data that has already been read. Re-store processing is performed with priority given to data that has not been read. For unsorted data that has not been re-stored, for example, the position information of the data is managed in an ascending list.

  This will be described with reference to FIG. The distributed storage control unit 25 starts reading processing for all data in the storage device 31 (step S1). As an example of such processing, there is read processing from the master site that is performed at the time of replication. In this type of read process, after the read process up to a certain position in the storage device 31 is completed, the read process is continued from the completed position.

  In replication, when data is written to a file on the master site side, differential data accompanying the writing is transferred from the master site to the replica site. Since the transfer target is a difference, the data once read by replication is not referred to thereafter. For this reason, the data subjected to the read process in the file on the master site side is not subjected to the read process thereafter.

Next, the distributed storage control unit 25 ends the reading process (step S2). The pointer indicating the position at this time is called a read pointer, and the position information of the read pointer is POS _R.

Next, the storage location management unit 26 holds the read pointer (position information) POS _R in the storage location information storage unit 32 (step S3).

Next, the storage position management unit 26 reads the position information POS _R of the read pointer and the end / restart position POS _P of the re-storing process from the storage position information storage unit 32 (step S4).

Next, the storage location management unit 26 compares the location POS _R and the location POS _P read from the storage location information storage unit 32 (step S5).

In the traveling direction of the reading process, when the position POS _R is in the forward of the position POS _P, i.e., the position POS _R to start the next read process than re-storing process for resuming position POS _P, data storage folder If it is located at the end of F1 to F12, the storage position management unit 26 uses the value of the end / restart position POS _P of the re-storing process stored in the storage position information storage unit 32 as the read pointer position POS _R. Update with a value (step S6). That is, the position POS _P at which the re-storing process is resumed is skipped to the position POS _R at which the next reading process is started.

At this time, as shown in FIG. 8, the restart position POS _P of the re-storing process is brought to the state of following the next start position POS _R of the preceding reading process. In the data storage files F <b> 1 to F <b> 12, priority is given to the re-storing process for data stored after the next start position of the reading process.

When the position POS _P is ahead of the position POS _R in the progress direction of the reading process, that is, the position POS _{R at} which the next reading process is started is more data than the position POS _{P at} which the re-storing process is restarted. If it is at the head of the storage folder F1 to F12, nothing is done.

Next, the divided storage control unit 25 starts the re-storage process from the position POS _P stored in the storage position information storage unit 32 (step S7).

  For example, in steps S6 and S7, when the storage system 10 is a storage device at the replication master site, the replication job notifies the read-out information storage unit 33 of the last read position at the end of the replication job. In addition, the replication job notifies the storage location management unit 26 that the read information has been updated. In response to this notification, the storage location management unit 26 refers to the read information storage unit 33 and sets the re-storage process start position to the position read from the read information storage unit 33. The divided storage control unit 25 starts the re-storing process from the reset position.

  According to this embodiment, the read performance of the content address storage system can be improved.

  A part or all of the above embodiment can be described as the following supplementary notes, but is not limited thereto.

(Appendix 1)
When data generated by dividing one parent data into a plurality of pieces is called child data, means for sequentially storing child data having different parent data as a division source in a file in the storage device,
Means for storing, in a storage device, a position at which the reading process was last read from the file in response to execution of the reading process of the file;
A storage system comprising means for performing a sorting process for sorting the child data in the file on the child file stored after the position.

(Appendix 2)
The storage system according to appendix 1, wherein the sorting process sorts the child data so that the child data having the same parent data as a division source is continuous in the file.

(Appendix 3)
The child data has an order relationship with other child data generated by dividing the same parent data,
The sorting process is performed so that the child data having the same parent data as a division source is continuous according to the order relation in the file.
The storage system according to appendix 1 or appendix 2.

(Appendix 4)
The content address storage system according to any one of appendix 1 to appendix 3.

(Appendix 5)
The storage system according to any one of appendix 1 to appendix 4, wherein the storage system is a storage system included in the master site that performs replication from a master site to a replica site.

(Appendix 6)
When the data generated by dividing one parent data into a plurality of child data is called child data, the step of storing child data having different parent data as a division source in a file in the storage device in order,
In response to execution of the file reading process, storing the position at which the reading process was last read from the file in a storage device;
A data sorting method, comprising: performing a sorting process for sorting the child data in the file on the child file stored after the position.

(Appendix 7)
The method according to claim 6, wherein the sorting process sorts the child data so that the child data having the same parent data as a division source is continuous in the file.

(Appendix 8)
The child data has an order relationship with other child data generated by dividing the same parent data,
The sorting process is performed so that the child data having the same parent data as a division source is continuous according to the order relation in the file.
The method according to appendix 6 or appendix 7.

(Appendix 9)
9. The method according to any one of appendix 6 to appendix 8, wherein the storage system is a content address storage system.

(Appendix 10)
The method according to any one of appendix 6 to appendix 9, wherein the storage system is a storage system included in the master site that performs replication from a master site to a replica site.

(Appendix 11)
When data generated by dividing one parent data into a plurality of pieces is called child data, means for sequentially storing child data having different parent data as a division source in a file in the storage device,
Means for storing, in a storage device, a position at which the reading process was last read from the file in response to execution of the reading process of the file;
A program for causing a computer to realize means for sorting the child data in the file with respect to the child file stored after the position.

(Appendix 12)
The program according to claim 11, wherein the sorting process sorts the child data so that the child data having the same parent data as a division source is continuous in the file.

(Appendix 13)
The child data has an order relationship with other child data generated by dividing the same parent data,
The sorting process is performed so that the child data having the same parent data as a division source is continuous according to the order relation in the file.
The program according to appendix 11 or appendix 12.

1, 10 Storage system 21 Stream ID assigning unit 22 Block generation unit 23 Duplicate check unit 24 Fragment generation unit 25 Distributed storage control unit 26 Storage location management unit 30 Data storage device 31 Storage device 32 Storage location information storage unit 33 Read information storage Part

Claims (10)

When data generated by dividing one parent data into a plurality of pieces is called child data, means for sequentially storing child data having different parent data as a division source in a file in the storage device,
Means for storing, in a storage device, a position at which the reading process was last read from the file in response to execution of the reading process of the file;
A storage system comprising means for performing a sorting process for sorting the child data in the file on the child file stored after the position.   The storage system according to claim 1, wherein the sorting processing sorts the child data so that the child data having the same parent data as a division source is continuous in the file. The child data has an order relationship with other child data generated by dividing the same parent data,
The sorting process is performed so that the child data having the same parent data as a division source is continuous according to the order relation in the file.
The storage system according to claim 1 or 2.   The content address storage system according to any one of claims 1 to 3.   The storage system according to any one of claims 1 to 4, wherein the storage system is a storage system included in the master site that performs replication from a master site to a replica site. When the data generated by dividing one parent data into a plurality of child data is called child data, the step of storing child data having different parent data as a division source in a file in the storage device in order,
In response to execution of the file reading process, storing the position at which the reading process was last read from the file in a storage device;
A data sorting method, comprising: performing a sorting process for sorting the child data in the file on the child file stored after the position.   The method according to claim 6, wherein the sorting process sorts the child data so that the child data having the same parent data as a division source is continuous in the file. The child data has an order relationship with other child data generated by dividing the same parent data,
The sorting process is performed so that the child data having the same parent data as a division source is continuous according to the order relation in the file.
8. A method according to claim 6 or claim 7. When data generated by dividing one parent data into a plurality of pieces is called child data, means for sequentially storing child data having different parent data as a division source in a file in the storage device,
Means for storing, in a storage device, a position at which the reading process was last read from the file in response to execution of the reading process of the file;
A program for causing a computer to realize means for sorting the child data in the file with respect to the child file stored after the position.   The program according to claim 9, wherein the sorting process sorts the child data so that the child data having the same parent data as a division source is continuous in the file.

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