KR20090007926A - Apparatus and method for managing index of data stored in flash memory - Google Patents

Abstract

An index information management apparatus of data effectively stored in a flash memory through cluster and a method thereof are provided to reflect the physical properties of the memory. An index generation part confirms with whether an index-page exists in the flash memory(S500). The whole record stored in flash memory is read the index generation part(S510). An index generation part stores an index-page in which the flash page is allocated from the flash memory(S530). A directory management part reflects the indexing information of the index-page stored in the flash memory(S540). The index generation part confirms whether the index entry comprises index-page(S550).

Description

Apparatus and method for managing index of data stored in flash memory}

1 is a block diagram showing a detailed configuration of a preferred embodiment of an apparatus for managing index information of data stored in a flash memory according to the present invention;

2 is a diagram illustrating an example of an index page stored in a flash memory;

3 is a diagram showing an example of a buffer entry stored in an update delay buffer unit;

4 is a block diagram showing a detailed configuration of an index management unit;

5 is a flowchart illustrating a process of performing a bulk-load operation for generating an index page in the apparatus for managing index information according to the present invention;

6 is a flowchart illustrating a process of performing a preferred embodiment of the index information management method according to the present invention;

7 is a flowchart illustrating a process of performing an embodiment of an insertion or deletion operation in the index information management apparatus according to the present invention;

8 is a flowchart illustrating a process of performing another embodiment of an insertion or deletion operation in the index information management apparatus according to the present invention;

9 is a flowchart illustrating a process of performing another embodiment of an insertion or deletion operation in the index information management apparatus according to the present invention;

10A and 10B are diagrams illustrating data of a flash memory and an update delay buffer unit, which are units of a unit merge operation, respectively;

11 is a flowchart illustrating a process of performing a unit merge operation in the index information management method according to the present invention;

12 is a flowchart illustrating a specific configuration of a page reconstruction step of the unit merge operation illustrated in FIG. 11;

FIG. 13 is a diagram illustrating a result of merging a unit merging unit and a unit merging set in a main memory during unit merging; and

14 is a flowchart illustrating a process of performing a search operation in the index information management method according to the present invention.

The present invention relates to an apparatus and method for managing index information of data stored in a flash memory, and more particularly, to an apparatus and method for generating and managing index information for efficiently processing various operations occurring on data stored in a flash memory. It is about.

Flash memory is composed of consecutive blocks of the same size, and one block is composed of consecutive pages of the same size. There are three operations that can be performed in flash memory: read, write and erase. Read and write operations are performed in units of pages, and erase operations are performed in units of blocks. At this time, the write operation takes more execution time than the read operation, and causes an erase operation that requires more execution time than the write operation. Therefore, reducing the number of write operations improves the overall performance of the flash memory.

Such flash memory is currently used as a main storage device in many fields, but is distinguished from other storage devices.

The first characteristic of flash memory is that there is a big difference in the speed of read, write and erase operations. The read and write operations of the flash memory are performed in units of pages, and the time to write a page is about 20 times slower than the read operation. In addition, the erase operation is performed in a block unit composed of several pages, which is 200 times slower than the read speed.

The second characteristic of flash memory is that the write operation can be performed only on the page where the erase operation is performed. That is, even if the data stored in the flash memory is updated, it is impossible to overwrite the same page and must be written to a new blank page. At this time, there is an additional load to copy all other valid data existing in the page where the data to be updated is stored. The existing page is made ready to be written again later through an erase operation.

The third characteristic of flash memory is that its life is determined. Each block on the page that makes up the flash memory is no longer available after 100,000 to 1,000,000 erase operations. As a result, frequent overwriting of flash pages results in a rapid exhaustion of empty pages, which in turn causes an erase operation to provide the empty pages, resulting in a shorter flash memory life.

Due to the characteristics of the flash memory as described above, the indexing method applied to the existing general storage device is not suitable for the flash memory. The most typical index structure of the related art is a B + tree. The B + tree is designed to effectively reduce disk I / O, which is the main cause of performance reduction in hard disk-based indexes. The result is a significant performance improvement and is the most widely used index structure in current hard disk-based database systems.

If the B + tree is used as it is in flash memory, when a record is inserted or deleted, the flash page cannot be overwritten on the same page even though there is free space. Therefore, a new page must be allocated to save the changed state of the node. At this time, if overflow or underflow occurs, the node is divided or merged, which affects the parent node. In other words, new pages must be allocated and copied in the flash page corresponding to the upper node. In a B + tree, such splitting and merging can occur cascaded from leaf nodes to root nodes. The B + tree, which causes frequent overwriting by inserting and deleting data, shortens the life of flash memory due to the physical characteristics of flash memory, and expects the same performance as that of the hard disk in performing various operations occurring in the index. it's difficult.

A conventional index structure based on flash memory is a B-Tree Flash Translation Layer (BFTL) that improves B-trees to suit the characteristics of flash memory. As shown in the problem of the implementation of B + tree for flash memory, even if there is free space on the page, the space cannot be utilized. Therefore, in BFTL, when writing index entries to a flash page, even though entries belonging to different index nodes are stored in a single flash page as much as possible, unlike B-trees.

As such, unlike the B-tree, the BFTL has an entry belonging to a different index node in one flash page. Therefore, an additional mechanism is required to show an application that uses the BFTL the same as using the B-tree. First, BFTL needs a mechanism to identify the physical storage location of entries belonging to the same index node. To do this, BFTL uses a data structure called a node translation table. The node translation table is a collection having as its elements a linked list of addresses in which index entries belonging to the same node are stored. The node translation table resides in main memory, and its size increases as the number of nodes increases, thereby increasing the usage of main memory. Index search in BFTL is performed by building index nodes in main memory using this node translation table. This process requires access to a number of different flash pages, which reduces search performance and increases main memory usage to build index nodes. Next, in BFTL, the index entries stored on the flash page each contain additional information indicating the node to which they belong. If splitting or merging of index nodes occurs, this additional information causes update of index entries distributed and stored in multiple pages. As a result, all flash pages containing target index entries must be copied to a new page.

As described above, BFTL reduces the load due to unnecessary copying of data by storing entries belonging to different index nodes in one flash page, and reduces the number of pages written by filling the flash page. However, due to its structure, BFTL increases the main memory usage and decreases the search performance, and incurs the load of multiple flash pages being copied when the index node is split or merged.

An object of the present invention is to reduce the number of write and erase operations of a flash page due to dynamic insertion and deletion of an index in consideration of the physical characteristics of the flash memory, and index entries for data stored in the flash memory. The present invention provides an apparatus and method for managing index information of data stored in flash memory that can support fast retrieval by effectively clustering them and ensure the efficiency of storage space by increasing utilization of flash pages.

Another object of the present invention is to reduce the number of write and erase operations of a flash page due to dynamic insertion and deletion of an index in consideration of the physical characteristics of the flash memory, and to index the data stored in the flash memory. By effectively clustering entries, you can support fast retrieval, and you can use a computer that has recorded a program to run index information management of data stored in flash memory that can increase the utilization of flash pages to ensure the efficiency of storage space. To provide a record carrier.

In order to achieve the above technical problem, an apparatus for managing index information of data stored in a flash memory according to the present invention includes calculation target data stored in or to be stored in the flash memory and a type of operation to be performed on the calculation target data. An update delay buffer unit for storing a buffer entry; Instructing the update delay buffer unit to generate a buffer entry corresponding to the operation to be performed when an instruction to perform an insert operation for recording operation target data or a delete operation for removing operation target data from the flash memory is instructed. A buffer entry generating unit for storing; And a plurality of index entries including key values of records stored in the flash memory and record position information until the update delay buffer unit is empty when the storage available space of the update delay buffer unit becomes smaller than a preset threshold. A predetermined number of index pages are selected as merge target pages among the index pages, the index entries recorded in the merge target pages are read and loaded into the main memory, and the buffer entries stored in the update delay buffer unit are stored in the main memory. And an index manager configured to sequentially insert between index entries loaded in the memory to configure an index page to be written to the flash memory.

According to another aspect of the present invention, there is provided a method of managing index information of data stored in a flash memory according to the present invention, which comprises: (a) insert operation for recording operation target data into a flash memory or operation target data from the flash memory; When an instruction to perform a delete operation is performed to remove a buffer, an update delay is generated by generating a buffer entry including operation target data stored in or stored in flash memory and a type of operation to be performed on the operation target data corresponding to the operation to be performed. Storing in a buffer; (b) when the storage available space of the update delay buffer unit is smaller than a preset threshold, a predetermined number of index pages including a plurality of index entries including key values of records and position information of records from the flash memory are merged. Selecting a step; And (c) reading and loading the index entry recorded in the merge target page into the main memory, and sequentially inserting buffer entries stored in the update delay buffer between the index entries loaded into the main memory and flashing them. Constructing an index page to be written to a memory.

Accordingly, the lifespan of the flash memory can be extended by reducing the number of write and erase operations of the flash memory, and the efficiency of the storage space can be guaranteed by increasing the utilization of the flash page.

Hereinafter, a preferred embodiment of an apparatus and method for managing index information of data stored in a flash memory according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram showing a detailed configuration of a preferred embodiment of the apparatus for managing index information of data stored in a flash memory according to the present invention.

Referring to FIG. 1, the apparatus 100 for managing index information of data stored in a flash memory includes an index generator 110, a buffer entry generator 120, an update delay buffer 130, an index manager 140, and a main controller. The memory 150 includes a buffer manager 160, a directory manager 170, and a searcher 180.

If there is no index page in the flash memory 190, the index generator 110 generates an index entry for all records stored in the flash memory 190, and then indexes a preset number of indexes. An index page composed of entries is generated and stored in a blank page of the flash memory 190. As described above, an operation of constructing an index page based on data stored in the flash memory 190 by the index generator 110 is called a bulk-load operation.

2 illustrates an example of an index page stored in the flash memory 190. 2, an index 210 and a flash page 240 are stored in the flash memory 190. The index 210 is a set of index pages, and the index page 220 is a unit for storing index entries. Each index page is stored in correspondence with a flash page, and index pages that are logically contiguous in the index need not be physically contiguous in the flash memory 190. Index page 220 includes a number of index entries 230. The index entry 230 basically includes operation target data (ie, a key value of a record) and position information of the calculation target data. Each index page may have empty space according to the number of index entries it contains, and the index entries in the index pages are stored in alignment according to the size of the key value of the record. In this case, the key value of the record means an actual value of a field for identifying a corresponding record, and the record position information means an address of a record stored in the flash memory 190.

The buffer entry generating unit 120 corresponds to an operation to be performed when an insert operation for recording the operation target data or an erase operation for removing the operation target data from the flash memory 190 is instructed to the flash memory 190. Create a buffer entry. The buffer entry basically includes operation target data (ie, a key value of a record) stored in or to be stored in the flash memory 190, position information of the operation target data, and a type of operation to be performed on the operation target data. The buffer entry may be maintained in a different form in the update delay buffer unit 130 or include additional information according to the entry storage structure. For example, the buffer entries may be stored in the update delay buffer unit 130 in the order of key values. In this structure, there is a load to maintain the sorted order when inserting and deleting buffer entries, but there is an advantage that an efficient search for entries can be performed through binary search. In this case, when different operations are generated for the same record, only the buffer entries related to the latest operation are maintained in the update delay buffer unit 130. As another example, when the buffer entries are stored in the form of a binary search tree in the update delay buffer unit 130, the buffer entry further includes a left child pointer and a right child pointer. In such a structure, there is a load to maintain the buffer entries in the form of a binary search tree, but there is an advantage that the insertion, deletion, and retrieval of entries in the update delay buffer unit 130 can be efficiently performed. Even in this case, only the buffer entry related to the latest operation is maintained in the update delay buffer unit 130 for the same record.

The update delay buffer unit 130 stores the buffer entry generated by the buffer entry generator 120. The update delay buffer unit 130 is maintained in a fixed size in the main memory 150 or configured as a separate storage means, and is a device for temporarily storing and managing index entries dynamically inserted or deleted. 3 illustrates an example of buffer entries 310, 320, 330, 340, and 350 stored in the update delay buffer unit 130.

When the storage delay of the update delay buffer unit 130 is smaller than a preset threshold value (for example, 10%, 0%, etc.) of the update delay buffer unit 130, the index delay unit 130 Until a blank page is merged, a predetermined number (for example, two) of index pages including a plurality of index pages including a key value of a record and position information of the record stored in the flash memory 190 are merged. To be selected. In addition, the index manager 140 reads the index entries recorded in the selected merge target page, loads them into the main memory 150, and then loads the buffer entries stored in the update delay buffer unit 130 into the main memory. The index pages to be written to the flash memory 190 are sequentially inserted between the entries.

4 is a block diagram illustrating a detailed configuration of the index manager 140.

Referring to FIG. 4, the index manager 140 may include a page selector 410, an entry selector 420, a page constructer 430, a preprocessor 440, an identification information allocator 450, and an entry distributor. 460.

The page selector 410 may include a plurality of records including key values of records stored in the flash memory 190 and record position information when the storage space of the update delay buffer 130 is smaller than a preset threshold. A predetermined number (for example, two) of index pages among the index pages formed of the index entries are selected as the merge target page.

The entry selector 420 selects the number of buffer entries corresponding to the recordable spaces identified from the merge target pages among the buffer entries stored in the update delay buffer unit 130 as mergeable entries.

The page constructing unit 430 sequentially inserts the mergeable entry between the index entries loaded in the main memory 150 based on the size of the operation target data to form a temporary index page. At this time, if the buffer entries have a structure that is stored in the update delay buffer unit 130 in the order of occurrence of the operation, the preprocessing process for the buffer entries stored in the update delay buffer unit 130 before constructing the temporary index page. need.

The preprocessing unit 440 sorts the buffer entries stored in the update delay buffer unit 130 based on the size of the calculation target data, and if different calculation types are set for the same calculation target data, the preprocessing unit 440 performs temporal processing among the same calculation target data. As a result, except for the buffer entry corresponding to the operation target data stored in the update delay buffer unit 130 and the corresponding operation type, the buffer entry corresponding to the remaining operation target data and the operation type is removed. When the insertion and deletion operations are repeatedly performed on the same key value in the update delay buffer unit 140 by the operation of the preprocessing unit 440, merge operation of the latest information is possible.

The identification information allocating unit 450 allocates the first page identification information to the temporary index page in which the insertion or deletion operation is performed by the mergeable entry among the temporary index pages, and the insertion or deletion operation by the mergeable entry is not performed. Second page identification information is allocated to the non-temporary index page, and the first page identification information is allocated to the remaining temporary index pages. The reason for distinguishing the temporary index pages as described above is to allow the minimum write operation to be performed under the condition that the utilization rate of the flash page satisfies 50% or more when constructing and storing the index.

The entry allocator 460 allocates the temporary index page to which the second page identification information is allocated before or after the temporary index page in which the page utilization rate is lower than the preset reference utilization rate among the temporary index pages to which the first page identification information is assigned. After allocating the first page identification information to the first page identification information, the entries constituting the temporary index page having the page utilization rate lower than the preset reference utilization rate are allocated to the temporary index page to which the first page identification information is allocated to the flash memory 190. Configure the index page to be written.

The main memory 150 stores index pages read from the flash memory 190 for performing a merge operation. In addition, the main memory 150 stores mergeable entries selected from the update delay buffer unit 130 when the merge operation is performed. Furthermore, the main memory 150 stores intermediate data generated while the index information management apparatus 100 according to the present invention creates or updates an index. The update delay buffer unit 130 may be fixedly allocated from the main memory 150.

When the buffer management unit 160 is instructed to perform an insert or delete operation, the buffer manager 160 records the buffer entry generated corresponding to the operation target data in the update delay buffer unit 130. The management operation of the update delay buffer unit 130 of the buffer manager 160 is different depending on the structure of the buffer entry. For example, in the case where the buffer entry is managed in a form suitable for binary search, the buffer management unit 160 supplies the update delay buffer unit 130 with the same operation target data as the buffer entry generated by the buffer entry generation unit 120. If there is a buffer entry to be included, the operation type of the buffer entry existing in the update delay buffer unit 130 is changed to the operation type of the newly created buffer entry.

The directory manager 170 creates a directory for directly accessing the index page stored in the flash memory 190 in a logical order. The created directory is maintained and managed by the file system in the form of a file map when the file system exists. At this time, the file map should be inserted and deleted in the middle for efficient search. In contrast, if the file system does not exist, the directory is implemented in the same form as the file map provided by the file system.

The search unit 180 first searches for an update delay buffer unit 130 that stores the latest information when a search operation is requested, and provides a search result. At this time, if the search request value does not exist in the update delay buffer unit 130, the search unit 180 checks the directory, identifies the index page to perform the search operation, and performs a binary search within the index page. The searched value and provide the search result.

5 is a flowchart illustrating a bulk-load operation for generating an index page in the apparatus for managing index information according to the present invention.

Referring to FIG. 5, the index generator 110 checks whether an index page exists in the flash memory 190 (S500). If the index page does not exist, the index generator 110 reads the entire record stored in the flash memory 190 and generates an index entry to configure the index page (S510). Next, the index generator 110 generates an index page composed of index entries corresponding to a page fill factor input from the outside or a preset page fill factor (that is, the number of index entries that can fit in one index page) (S520). ). Next, the index generator 110 stores the index page generated by allocating a flash page from the flash memory 190 (S530). Next, the directory manager 170 reflects indexing information about the index page stored in the flash memory 190 in the directory (S540). Finally, the index generator 110 checks whether an index entry for constituting the index page exists (S550), and if the index entry does not exist, ends the bulk-load operation.

6 is a flowchart illustrating a process of performing a preferred embodiment of the index information management method according to the present invention.

Referring to FIG. 6, when an instruction to perform an insert or delete operation on a record is instructed (S600), the buffer manager 160 updates a buffer entry including a key value and an operation type of a record corresponding to the indicated operation. Record at 130 (S610). Next, the index manager 140 checks whether the spare capacity of the update delay buffer unit 130 is smaller than a preset reference value (S620). If the spare capacity is smaller than a preset reference value, the index manager 140 reads an index entry from a preset number of index pages from the flash memory 190 and loads the index entry into the main memory 150 (S630). Next, the index manager 140 reconstructs the index page by merging the index entries loaded in the main memory 150 and the number of mergeable entries selected from the update delay buffer unit 130 (S640). Next, the index manager 140 checks whether a buffer entry exists in the update delay buffer unit 130 (S650). If there is a buffer entry, the index manager 140 performs steps S630 to S640. In contrast, if the buffer entry does not exist, the directory manager 170 reflects the index information of the reconstructed index page to the directory (S660).

7 is a flowchart illustrating a process of performing an embodiment of an insertion or deletion operation in the index information management apparatus according to the present invention. The embodiment shown in FIG. 7 corresponds to a case where buffer entries are sequentially stored in empty spaces of the update delay buffer unit 130 according to when an operation occurs.

Referring to FIG. 7, when an instruction for inserting or deleting a record is performed, the buffer manager 160 searches for the first free space of the update delay buffer 130 (S700). Next, the buffer manager 160 inserts a new buffer entry into the searched empty space (S710). Next, the index manager 140 checks whether the free space exists in the update delay buffer unit 130 (S720). If the free space does not exist, the index manager 140 performs a merge operation (S730). Although the embodiment described with reference to FIG. 7 is effective at inserting and deleting index entries, the search time in the update delay buffer unit 130 is slow.

8 is a flowchart illustrating a process of performing another embodiment of the insertion or deletion operation in the index information management apparatus according to the present invention. The embodiment shown in FIG. 8 corresponds to a case where the buffer entry is stored in the update delay buffer unit 130 according to the size of the key value.

Referring to FIG. 8, when an instruction to insert or delete a record is performed, the buffer manager 160 searches for a buffer entry having the same key value as the new buffer entry through binary search for the update delay buffer unit 130. (S800). Next, if there is a buffer entry of the same key value (S810), the buffer manager 160 deletes the existing buffer entry (S820). Next, the buffer manager 130 stores the new entry in the update delay buffer 130 and sorts the entries of the update delay buffer 130 based on the key value (S830). Next, the index manager 140 checks whether the free space exists in the update delay buffer unit 130 (S840). If the free space does not exist, the index manager 140 performs a merge operation (S850). In the embodiment shown in Fig. 8, there is a load that maintains the sorted order upon insertion and deletion of buffer entries. However, when different operations on the same record occur, only the latest operation is maintained, so that the search for the update delay buffer unit 130 can be efficiently performed through binary search.

9 is a flowchart illustrating a process of performing another embodiment of an insertion or deletion operation in the index information management apparatus according to the present invention. The embodiment shown in FIG. 9 corresponds to the case where the buffer entry is stored in the update delay buffer unit 130 in the form of a binary search tree.

Referring to FIG. 9, when an instruction to insert or delete a record is performed, the buffer manager 160 searches for a buffer entry having the same key value as a new buffer entry through binary search for the update delay buffer unit 130. (S900). Next, if there is a buffer entry of the same key value (S910), the buffer manager 160 deletes the existing buffer entry (S920). Next, the buffer manager 130 stores the new entry in the update delay buffer unit 130 and updates the information of the entries so that the entries of the update delay buffer unit 130 maintain the binary search tree structure (S930). Next, the index manager 140 checks whether the free space exists in the update delay buffer unit 130 (S940). If the free space does not exist, the index manager 140 performs a merge operation (S950). In the embodiment shown in Fig. 9, only the latest operation is maintained when different operations on the same record occur, so that all the insertion, deletion, and retrieval of buffer entries can be efficiently performed. exist.

When buffer entries are continuously stored in the update delay buffer unit 130 through the insert operation or the delete operation as described above with reference to FIGS. 7 to 9, the free capacity of the update delay buffer unit 130 is greater than the preset threshold. It becomes small. In this case, the index manager 140 merges the buffer entries stored in the update delay buffer unit 130 with the index entries of the index pages stored in the flash memory 190 and performs a merge operation for reconstructing the index pages. . In this case, the merge operation is performed in a form in which a unit merge operation performed on a predetermined number of index pages is performed a plurality of times, and is performed until the update delay buffer unit 130 is empty.

10A and 10B, data of the flash memory 190 and data of the update delay buffer unit 130, which are the targets of the unit merge operation, are shown.

10A and 10B, the unit merging unit 1000 is a set consisting of a predetermined number of index pages 1010 and 1020. At this time, the range of key values to be stored in the unit mergeable unit 1000 during unit merge operation is defined as a unit mergeable range. If the unit merge operation is performed on the i th index page to the k index pages, the unit merge possible range is between the minimum value of the i th index page and the minimum value of the (i + k + 1) th index page. The zeroth index page refers to a virtual index page that exists to perform unit merging on index entries existing between an infinite number corresponding to a range that cannot be occupied in the index page and a minimum value of the first index page. In the example shown in FIG. 10A, the unit merging possible range of the unit merging unit is greater than or equal to 11 and smaller than 51. The index page 1010 is divided into an occupied area 1012 in which an index entry is recorded and a non-occupied area 1014 in which an index entry is not recorded. On the other hand, the unit merging set 1030 is a set composed of the number of buffer entries corresponding to the non-occupied area of the index pages included in the unit merging possible range among the buffer entries of the update delay buffer unit 130. In the example shown in FIG. 10B, the buffer entries forming the unit mergeable set are (12, insert), (15, delete), (41, insert), and (42, insert).

11 is a flowchart illustrating a process of performing a unit merge operation in the index information management method according to the present invention.

Referring to FIG. 11, the page selector 410 records key values and record position information of a record stored in the flash memory 190 when the storage available space of the update delay buffer unit 130 is smaller than a preset threshold. A predetermined number (for example, two) of index pages including a plurality of index pages including a plurality of index entries including a target page is selected as a merge target page, and the index entries of the merge target page are loaded into the main memory 150 (S1100). ). Next, the entry selecting unit 420 selects the number of buffer entries corresponding to the non-occupied area identified from the merge target pages among the buffer entries stored in the update delay buffer unit 130 as mergeable entries (S1110). ). Next, the page constructing unit 430 reconstructs the index page by sequentially inserting mergeable entries between index entries loaded in the main memory 150 based on the size of the key value (S1120). At this time, if the buffer entries have a structure that is stored in the update delay buffer unit 130 in the order of occurrence of the operation, the preprocessing process for the buffer entries stored in the update delay buffer unit 130 before constructing the temporary index page. need.

12 is a flowchart illustrating a specific configuration of a page reconstruction step of the unit merge operation illustrated in FIG. 11.

Referring to FIG. 12, first, the page constructing unit 430 sequentially inserts a mergeable entry between index entries loaded in the main memory 150 based on the size of a key value to construct a temporary index page (S1200). . Next, the identification information allocating unit 450 allocates the first page identification information to the temporary index page in which the insertion or deletion operation is performed by the mergeable entry among the temporary index pages, and the insertion or deletion operation is performed by the mergeable entry. The second page identification information is allocated to the temporary index page that has not been performed (S1210).

Here, the index page to which the first page identification information is assigned means an index page in which a buffer entry belonging to an occupied area of the unit mergeable unit exists. That is, the page to which the first page identification information is assigned refers to an index page which must be overwritten as a result of the merge operation. In the case of the embodiment illustrated in FIG. 10A, the left index page 1010 of the unit mergeable unit 1000 corresponds to such a page. In addition, the index page to which the second page identification information is assigned means an index page in which no buffer entry belonging to the occupied area among the unit mergeable units exists. That is, the page to which the second page identification information is assigned means an index page which may or may not be overwritten due to a merge operation. In the case of the embodiment illustrated in FIG. 10A, the right index page 1020 of the unit mergeable unit 1000 corresponds to such a page.

Next, the entry distribution unit 460 checks the number of index entries of the temporary index page to which the first page identification information is assigned (S1220). If there is a temporary index page in which the number of index entries of the temporary index page to which the first page identification information is allocated is less than or equal to half of the number of storeable entries (ie, page fill factor) set for the index page (S1230), the entry allocator 460 ) Changes the identification information of the temporary index page to which the second page identification information adjacent to the temporary index page is assigned to the first page identification information (S1240). Steps S1220 to S1240 are repeatedly performed on all temporary index pages to which first page identification information is assigned.

Next, the entry distribution unit 460 checks whether there is a page that can reduce the number of page writes among the temporary index pages to which the second page identification information is assigned (S1250). If such a temporary index page exists, the identification information of the corresponding page is changed to the first page identification information (S1260). Next, the entry allocator 460 equally distributes the mergeable entries selected from the update delay buffer unit 130 to the temporary index page to which the first page identification information is assigned, and reconstructs the index page to be stored in the flash memory 190. (S1270). Finally, the entry distributor 460 stores the reconstructed index page in the flash memory 190 (S1280).

FIG. 13 is a diagram illustrating a result of merging a unit mergeable unit and a unit mergeable set in the main memory 150 during unit merge operation.

Referring to FIG. 13, the number of index entries of the temporary index page 1330 appearing second from the temporary index pages 1310 and 1330 to which the first page identification information is assigned in allocating the corresponding index entries to the flash pages is one number. Less than half the total number of index entries that an index page can hold. Therefore, the identification information of the temporary index page 1320 to which the second page identification information is assigned among the temporary index pages existing before the corresponding index entries is changed into the first page identification information. Next, since there is no longer a temporary index page to which second page identification information is assigned, FIG. 8 index entries are equally distributed to two flash pages 1340 and 1350.

When the insert and delete operations are performed by the method described with reference to FIGS. 11 to 13, the number of write operations can be greatly reduced while ensuring the utilization rate of the index page by 50% or more. An exception is that pages with less than 50% utilization may be generated when there are many delete operations, but the existence of such pages may be allowed to reduce the number of write operations. In addition, when the size of the unit mergeable unit is 1 for the purpose of performance improvement, the merge operation on the 0 th node may be performed at the same time as the merge operation of the first index page.

In the present invention, since the update delay buffer is used instead of immediately applying the insert and delete operations to the index, the search operation is modified as follows. That is, the search operation in the index is first performed on the update delay buffer unit 130 which stores the latest information. If the requested value does not exist in the update delay buffer unit 130, the index page is searched through the directory.

14 is a flowchart illustrating a process of performing a search operation in the index information management method according to the present invention.

Referring to FIG. 14, when a search operation occurs, the search unit 180 first searches for an update delay buffer unit 130 that stores the latest information (1400). At this time, in the structure in which the buffer entries are stored in the chronological order in which they are generated, the search unit 180 sequentially searches from behind the update delay buffer unit 130. In contrast, in the structure in which the buffer entries are stored in the order of the key values or in the binary search tree structure, the search unit 180 performs a binary search on the update delay buffer unit 130. Next, the search unit 180 checks whether there is a search request value in the update delay buffer unit 130 (S1410). If the search request value exists in the update delay buffer unit 130, the search unit returns the address of the corresponding value (S1420). In contrast, if the search request value does not exist in the update delay buffer unit 130, the search unit 180 searches the directory to find an index page to perform a search operation (1430). Next, the search unit 180 performs a binary search in the index page to search for a value requested for search (1440). If the search request value exists in the index page, the search unit 180 returns the address of the corresponding value (1450). In contrast, if the search request value does not exist in the index page, the search unit 180 returns an error (1460).

The invention can also be embodied as computer readable code on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like, and may also be implemented in the form of a carrier wave (for example, transmission over the Internet). Include. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

Although the preferred embodiments of the present invention have been shown and described above, the present invention is not limited to the specific preferred embodiments described above, and the present invention belongs to the present invention without departing from the gist of the present invention as claimed in the claims. Various modifications can be made by those skilled in the art, and such changes are within the scope of the claims.

According to the apparatus and method for managing index information of data stored in a flash memory according to the present invention, by efficiently clustering index entries, an efficient search can be performed while increasing the utilization rate of a flash page. In addition, by delaying dynamic insertion and deletion in consideration of the physical characteristics of the flash memory, it is possible to extend the life of the flash memory by reducing the number of write and erase operations of the flash memory. Furthermore, it uses less memory and operates at lower power, so it can be applied in mobile or embedded systems.

Claims (15)

An update delay buffer unit configured to store buffer entries including operation target data stored in or to be stored in flash memory and types of operations to be performed on the operation target data; Instructing the update delay buffer unit to generate a buffer entry corresponding to the operation to be performed when an instruction to perform an insert operation for recording operation target data or a delete operation for removing operation target data from the flash memory is instructed. A buffer entry generating unit for storing; And When the storage space of the update delay buffer unit becomes smaller than a preset threshold, the index may include a plurality of index entries including key values of records stored in the flash memory and record position information until the update delay buffer unit is empty. A predetermined number of index pages are selected as a merge target page among index pages, the index entries recorded in the merge target page are read and loaded into the main memory, and the buffer entries stored in the update delay buffer unit are stored in the main memory. And an index manager configured to sequentially insert between index entries loaded in the memory and to write an index page to be recorded in the flash memory. The method of claim 1, If the index page does not exist in the flash memory, the index entry is generated for all records stored in the flash memory, and then an index page composed of index entries corresponding to a predetermined reference number is created to generate an empty page of the flash memory. And an index generator for storing the data in a page. The method of claim 1, When the buffer entries stored in the update delay buffer unit are arranged based on the size of the key value of the operation target data, and different operation types are set for the same operation target data, the update delay buffer is delayed in time among the same operation target data. And a pre-processing unit for removing the buffer entry corresponding to the operation target data and the operation type except for the operation target data stored in the unit and the buffer entry corresponding to the operation type corresponding thereto. Index information generating device. The method of claim 1, Changing the operation type of the buffer entry existing in the update delay buffer unit to the operation type of the generated buffer entry if the buffer entry including the same operation target data as the generated buffer entry exists in the update delay buffer unit. Index information management apparatus for data stored in the flash memory, characterized in that it further comprises a buffer management unit. The method according to any one of claims 1, 3 or 4, The index manager selects a number of buffer entries corresponding to recordable spaces identified from the merge target pages as mergeable entries among the buffer entries stored in the update delay buffer unit, and selects the mergeable entry as the main entry. And an index page to be written to the flash memory by sequentially inserting the index entries loaded into the memory. The method according to any one of claims 1, 3 or 4, The index management unit, When the storage available space of the update delay buffer unit is smaller than a preset threshold, a predetermined number of index pages may be selected from an index page including a plurality of index entries including key values and record position information of a record stored in the flash memory. A page selector for selecting a merge target page; An entry selecting unit which selects, as mergeable entries, a number of buffer entries corresponding to recordable spaces identified from the merge target pages among buffer entries stored in the update delay buffer unit; A page constructing unit configured to sequentially insert the mergeable entry among the index entries loaded in the main memory based on the size of the key value of the operation target data to form a temporary index page; Among the temporary index pages, first page identification information is allocated to a temporary index page on which an insert or delete operation is performed by the mergeable entry, and to a temporary index page on which the insert or delete operation on the mergeable entry is not performed. An identification information allocator for allocating second page identification information to the second page and allocating the first page identification information to the remaining temporary index pages; And Among the temporary index pages to which the first page identification information is assigned, the first page identification information is assigned to the temporary index page to which the second page identification information which is located before or after the temporary index page whose page utilization rate is lower than the preset reference utilization rate is assigned. Entry for configuring an index page to be recorded in the flash memory by allocating entries constituting a temporary index page having a page utilization rate lower than a preset reference utilization rate to a temporary index page to which the first page identification information is allocated after reallocating Apparatus for index information generation of data stored in the flash memory comprising a; distribution unit. The method of claim 6, The entry allocator is configured to reset the first page identification information to the page with the highest page utilization rate among the temporary index pages to which the second page identification information located before or after the temporary index page whose page utilization rate is lower than the preset base utilization rate is assigned. And index information generating device for data stored in flash memory. (a) an operation to be stored or to be stored in the flash memory in response to the operation to be performed when an instruction to perform an insert operation for recording the operation target data or a delete operation for removing the operation target data from the flash memory is instructed to the flash memory; Generating a buffer entry including a target data and a type of operation to be performed on the operation target data and storing the buffer entry in an update delay buffer; (b) when the storage available space of the update delay buffer unit is smaller than a preset threshold, a predetermined number of index pages including a plurality of index entries including key values of records and position information of records from the flash memory are merged. Selecting a step; And (c) reading the index entries recorded in the merge target page and loading them into the main memory, and sequentially inserting the buffer entries stored in the update delay buffer between the index entries loaded into the main memory and then flash memory. And configuring an index page to be written in the index information management method of the data stored in the flash memory. The method of claim 8, (d) If the index page does not exist in the flash memory, the index entry is generated for all records stored in the flash memory, and then an index page composed of index entries corresponding to a predetermined reference number is generated. And storing the data in a blank page of the flash memory. The method of claim 8, (e) Sorting the buffer entries stored in the update delay buffer based on the size of the key value of the operation target data, and if the different operation types are set for the same operation target data, the update is performed later in the same operation target data. And removing the buffer entry corresponding to the remaining operation target data and the operation type except for the buffer entry corresponding to the operation target data stored in the delay buffer and the operation type corresponding thereto. Index information generation method. The method of claim 8, (f) changing the operation type of the buffer entry existing in the update delay buffer to the operation type of the generated buffer entry if the buffer entry including the same operation target data as the generated buffer entry exists in the update delay buffer. And managing the index information of the data stored in the flash memory. The method according to any one of claims 8, 10 or 11, In the step (c), among the buffer entries stored in the update delay buffer, the number of buffer entries corresponding to the recordable space identified from the merge target pages is selected as a mergeable entry, and the mergeable entry is selected. And index pages to be written in the flash memory by sequentially inserting the index entries loaded in the main memory. The method according to any one of claims 8, 10 or 11, Step (c) is, (c1) when the storage space of the update delay buffer becomes smaller than a preset threshold, a predetermined number of index pages including a plurality of index entries including key values of records and position information of records from the flash memory are merged. Selecting a step; (c2) selecting a number of buffer entries corresponding to recordable spaces identified from the merge target pages among the buffer entries stored in the update delay buffer as mergeable entries; (c3) constructing a temporary index page by sequentially inserting the mergeable entry between index entries loaded in the main memory based on the size of the key value of the operation target data; (c4) Allocate first page identification information to a temporary index page in which the insertion or deletion operation is performed by the mergeable entry among the temporary index pages, and the temporary insertion or deletion operation by the mergeable entry is not performed. Allocating second page identification information to the index page and allocating the first page identification information to the remaining temporary index pages; And (c5) a first index is assigned to a temporary index page to which second page identification information, which is located before or after a temporary index page having a page utilization rate lower than a preset reference rate, is allocated among the temporary index pages to which the first page identification information is assigned. After reallocating the page identification information, the entries constituting the temporary index page having the page utilization rate lower than the preset reference utilization rate are allocated to the temporary index page to which the first page identification information is allocated, thereby indexing the index page to be recorded in the flash memory. And indexing the data stored in the flash memory. The method of claim 13, In step (c5), the first page identification information is assigned to a page having a high page utilization rate among the temporary index pages to which the second page identification information located before or after the temporary index page whose page utilization rate is lower than a predetermined reference utilization rate is assigned. Index information generation method of the data stored in the flash memory, characterized in that for reallocating again. A computer-readable recording medium having recorded thereon a program for executing the method of generating index information of data stored in a flash memory according to any one of claims 8 to 11.

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