JPH03147032A - Data base control system - Google Patents

Abstract

PURPOSE:To update a data base even in the middle of back-up recording an updata transaction number in a record. CONSTITUTION:When a transaction (Tr) gives the request of the update of the data base, a data base updating control part 5 writes the record into the back up value page of the record when the update Tr number of the record is not included in a back up start time completion Tr list (CTRL) 4. When it is included in CTRL and the updating Tr number is not equal to the number of an updating request, the data base updating control part 5 writes the record into the pre-updating value page of the record. Then, the data base updating control part 5 writes the updating value of the record and the number of Tr which gives the updating request into a present value page, and writes a data base table identifier and the value of a record mainbody into a log. Thus, updating during back-up work is terminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a database management system that backs up a database without stopping database update operations.

(Prior art) In a database management system, even if a failure occurs in a non-volatile storage medium (hereinafter referred to as a secondary storage medium) such as a disk storing a database, it is necessary to restore the database to its current state. Must be. Therefore,
All records of the database are periodically copied to a secondary storage medium different from the one storing the database, and a log of update operations performed on the database from the time of copying is obtained. The process of copying database records is called backup, and the copied data is called backup data.

To recover a database from backup data and logs, you must perform a backup when the database is in the correct state and retrieve the logs from that point.

A database is in a correct state when a transaction (Tr), which is a logical unit of work for the database, is completed. While a transaction is being executed, the database is in a transient state and cannot be said to be in a correct state.

However, in the database management system, in order to access the database efficiently, a plurality of transactions simultaneously operate in parallel to search/update the database, as shown in FIG. Therefore, the database is rarely in the correct state during execution of a business program that accesses the database.

For this reason, conventionally, when backing up a database, operations that access the database have been stopped.

(Problems to be Solved by the Invention) However, in the conventional method, there is a problem in that it takes a considerable amount of time to back up the entire database, and transactions involving updates cannot be executed during this time. Particularly in an online processing system that operates without interruption for 24 hours, it is desirable to obtain backup data while executing online operations.

SUMMARY OF THE INVENTION An object of the present invention is to provide a database management system that solves these conventional problems and allows a database to be updated even during database backup work.

(Means for Solving the Problems) The present invention provides a database management system that stores pre-update images of database records stored in a secondary storage device and performs transaction failure recovery. When updating a record, an update transaction number is recorded in the record, and when updating a record during backup, if the transaction number of the update request is different from the transaction number recorded in the record, the pre-update value of the record is stored in the pre-update value storage area. and after saving it to the backup data storage area,
A database update control unit that updates the record, and when backing up the record stored in the secondary storage device, backs up any of the current value, pre-update value, and backup value of the record according to the update transaction number recorded in the record. A database backup control section that selects a database backup control section.

(Operation) Therefore, when updating a database record stored in the secondary storage device, the database update control unit records an update transaction number in the record. When updating records during backup, the database update control section:
When the transaction number of the update request is different from the transaction number recorded in the record, the record is updated after storing the pre-update value of the record in the pre-update value storage area and the backup data storage area. The transaction number of the update request is recorded in the record together with the update value of the record.

Therefore, backup work can be performed without stopping update work.

Furthermore, when backing up a record, the database backup control unit determines which of the record's current value, pre-update value, and backup value is to be backed up, based on the update transaction number recorded in the record, at the time of starting backup acquisition. Select depending on whether the transaction is completed or not. If a failure occurs in the medium on which the database is stored, the database can be recovered using backup data.

(Example) Next, embodiments of the present invention will be described using the drawings.

FIG. 1 is a block diagram showing an embodiment of the database management system of the present invention.

In the figure, 1 is a database management system, and this database management system 1 includes a transaction (Tr) number assignment table 2, a backup display flag 3, and a transaction completed at the start of backup (T
r) 4, a database update control section 5, a database backup control section 6, a database recovery control section 7, a request reception section 14, and a transaction (Tr) control section 15. Here, the Tr number assignment table 2 assigns a uniquely identifying transaction number (Tr number) to each transaction, and calculates the maximum value of the Tr number (
Since Tr numbers are assigned in order, the last assigned T
Refers to the value of r number. ) is stored. The backup in progress display flag 3 indicates whether or not a backup operation is in progress. The completed Tr list (CTRL) 4 at backup start is used to identify transactions that were completed at the time backup was started. Transactions that were completed at the time of backup start are, for example, the last value of the transaction number at the time of backup start (Tr numbers are assigned in order, so this refers to the value of the last assigned Tr number) and uncompleted T
It is determined from the value of r number. Further, the database update control unit 5 controls updating of records in the database. Further, the database backup control unit 6
A copy of the record of the database 9 is stored in another secondary storage device 8b. Further, the database recovery control unit 7 recovers the database from backup data and logs. Also, request reception is in Part 1.
4 accepts requests from external request sources that utilize the database management system 1. The Tr control unit 15 also controls the completion of transactions, assigns a unique Tr number to a transaction, and manages the state of the Tr.

Further, 8a is a secondary storage device using a non-volatile storage medium such as a disk for storing the database 9, and 8b is a non-volatile storage device such as a disk for storing backup data 11 of the database 9 and log data 13 of updates to the database 9. It is a secondary storage device using a storage medium. 1o is a collection of database tables 10'. 12 is backup data of the collection 10 of database tables 10'.

FIG. 3 is an internal configuration diagram of the database table 10'.

In the figure, a database table 10' is a collection of records 31. This record 31 consists of a record identifier 32 that uniquely identifies the record, a transaction number (this is referred to as an update Tr number) 33 that last updated this record, and a record body (record content) 34. Here, the record content 34 is used, for example, as user data.

FIG. 4 is a diagram showing the storage format of the database table.

41a and 41b are pages that store pointers pointing to pages that store records.

These pointers pointing to pages that store records increase or decrease depending on the increase or decrease in the number of pages that store records.

42a and 42b are pointers pointing to pages that store the current values of records.

43a and 43b are pointers pointing to pages that store pre-update values of records. 44a and 44b are pointers pointing to pages that store backup values of records. 45a and 45b are pages that store the current values of records. The value stored on this page is the latest value for the record. 46a and 46b are pages that store pre-update values of records. The values stored in this page are used when a transaction is aborted to return the records to the state they were in when the transaction began. 4
7a and 47b are pages that store backup values of records. Use this page to take backups while online.

In this way, three versions of the record value will be stored on the database 9.

Next, the operation of the embodiment of the present invention will be explained in different cases.

First, before updating records in the database 9, a request to start a transaction is sent from an external request source to the request receiving section 14 of the database management system 1. , transaction (T
r) Pass the request to the control unit 15. The Tr control unit 15 adds 1 to the contents of the Tr number assignment table 2, sets this as a Tr number that can uniquely identify the transaction, and assigns the transaction as a Tr number.
The request receiving section 14 responds to the external requestor for the r number.

(b) After the request source outside the normal update obtains the Tr number, it always adds the Tr number to the request to the database management system 1.

When the backup display flag is "false" and a backup operation is not in progress, if a transaction from an external request source makes a database update request, the request reception section 14 handles the request to the database update control section. Pass it to 5. The database update control unit 5 updates the database and writes a log according to the procedure shown in FIG. 5(a).

For example, if the current value of the record to be updated is stored in the record current value page 45a shown in FIG. 4, and the record to be updated is read from this current value page, the update Tr number of the record is If it is different from the Tr number (steps SL and S2 in FIG. 5(a)), after writing the value of the record on the current record value page 45a to the corresponding part of the pre-update page 46a in FIG. Update the record on the current record value page 45a, that is, write the updated value of the record and the number of the Tr that requested the update on the current value page of the record (step S in FIG. 5(a)
3. S4), and further writes the database table identifier, the record identifier, the Tr number that requested the update, and the value of the updated record body to the log (step S5 in FIG. 5(a)).

In addition, in step S2, when the update Tr number of the record and the Tr number that requested the update are equal, the process moves to step S4.

(b) Backup Data Acquisition When a request for database backup is supplied to the request receiving section 14 from an external request source, the request receiving section 14 receives the request from the database backup control section 6. The database 9 is backed up according to the procedure shown in Figure (b).

The backup data acquisition procedure shown in FIG. 5(b) will be explained.

The database backup control unit 6 sets the backup in progress display flag 3 to "true" (step 511). Next, the database backup control unit 6 writes the completed Tr to CTRL 4 (step 512), and writes the start of the backup work and the contents of CTRL 4 to the log (step 513).

The database backup control unit 6 checks whether all database tables have been backed up, and if all database tables have not been backed up, starts backing up the next database table (step S14,
515). If all records have been backed up, the process moves from step S16 to step S14. If not all records have been backed up, the database backup control unit 6 starts backing up the next record (steps 816 and 517). Next, the database backup control unit 6 reads the record from the current value page and saves that record. The update Tr number is CTRL4
If it is not included in CTRL4, select the record from the record's pre-update value page.
and checks whether the updated Tr number of the record is included in CTRL4 (steps S18 to S521).
) If the update Tr number of the record is not included in CTRL4, the database backup control unit 6 reads the record from the backup value page of the record and writes the record to the backup of the database table (steps S21 to 523). . After this, step S
23, the process moves to step S14. Also, step S
19, the update Tr number of the record is CTRL
4, or if the update Tr number of the record is included in CTRL4 in step S21, the process proceeds to step S19. The process moves from S21 to step S23.

If all the database tables are backed up by repeating the above operations, steps S14 to S24 are performed.
, and writes the completion of the backup operation to the log. Then, the database backup control unit 6 sets the backup in progress display flag 3 to "false".

In addition, in step S12, the database backup control unit 6 writes the completed Tr to CTRL4, but in this case, the completed Tr is written in the Tr number assignment table at the time of backup acquisition start (T back). Since it is determined from the last value of the Tr number stored in the Tr number and the uncompleted Tr number at the time of starting backup acquisition, instead of the completed Tr, the last value of the Tr number and the uncompleted Tr number at the time of starting backup acquisition are calculated. CTRL the Tr number
You can also write in 4.

Further, for example, assume that a backup is requested at time T back tl in FIG. 6(a). This T back
At time t, transaction (Tr,)1.
Transaction (Tr,)2 has already been completed, but Tr,2. Tr, 4 is in an incomplete state. However, in the present invention, the database in the state shown in FIG. 6(b) is backed up.

That is, if we look at each record in the database, T ba
Tr,2 and T, which have not been completed at Tback, after updating T',1 and Tr,3 which have been completed at time t,
The value of r,4 before the update is backed up.

(c) Update during backup operation If the backup operation display flag is “true” and a transaction from an external request source requests a database update while the backup operation is in progress, the database update control unit 5 Update the database and write the log according to the procedure shown in Figure (C).

The update procedure during the backup operation shown in FIG. 5(c) will be explained.

First, the database update control unit 5 reads the record to be updated from the current value page of the record, checks whether the update Tr number of the record is included in CTRL4, and if it is not included in CTRL4, the record is updated. Write to backup value page (step 326~
828) Note that in step S27, the record update Tr
When the number is included in CTRL4, the process moves to step S29. Next, when the update Tr number of the record is equal to the update requested number, the database update control unit 5 moves to step S31, and when the update Tr number of the record is not equal to the update requested number, the database update control unit 5 updates the record to the pre-update value of the record. Write on the page (step S29゜530). Next, the database update control unit 5 writes the update value of the record and the number of the Tr that requested the update to the current value page (step 531
), and further writes the database table identifier, the record identifier, the number of the Tr that requested the update, and the value of the updated record body into the log (step 532), thereby terminating the update during the backup operation.

For example, using FIG. 4, if the current value of the record to be updated is stored in the record's current value page 45a, and the updated Tr number of this record has not been completed when backup acquisition starts, and the updated If it is different from the Tr that made the request, the value of the record on the current value page 45a of the record is written to the corresponding part of the record backup value page 47a and the corresponding part of the record before update page 46a, and then the record value is update the record on the current value 45a (steps 326-5 of FIG. 5(C)
31).

(d) Database recovery If a failure occurs in the medium that stores the database, the
By copying the backup data 11 obtained in step (b) from the secondary storage device 8b to the database 9 of the secondary storage device 8a according to the procedure shown in FIG. 533), the database 9 is updated using this database 9 and the update log of the Tr that was incomplete at the time of T back, and the log is acquired to restore the database to the last transaction execution state (step 534).

As can be seen from the above explanation, in the present invention, when updating a record during backup, the transaction number that requested the update is recorded in the record along with the updated value, and the value of the record before the update is recorded on the backup value page of the record. Since it is saved, you can perform backup work without stopping update work.

The present invention is not limited to this embodiment, and various applications and modifications can be made without departing from the gist of the present invention.

(Effects of the Invention) As described above, by using the present invention, when updating a record that is being backed up, when the transaction number of the update request is different from the transaction number recorded in the record, the pre-update value of the record is stored in the pre-update value storage area. Since the record is updated after being saved in the backup data storage area, backup work can be performed without stopping the update work. Further, according to the present invention, if a failure occurs in the medium on which the database is stored, the database can be recovered using backup data.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the operational status of transactions within a database, FIG. 3 is an internal configuration diagram of a database table 10', and FIG.
FIG. 5 is an explanatory diagram of the storage format of the database table 10', FIG. 5 is an operation flowchart of FIG. 1, and FIG. 6 is an explanatory diagram showing the state of the database. 1... Database management system, 2... Tr number assignment table, 4... Completion list at backup start (CTRL),
5... Database update control unit, 6... Database backup control unit, 7... Database recovery control unit, 8a, 8b... Secondary storage device, 9... Database, 10'... Database Table, 11... Backup data, 12'... Backup data of database table. Explanation of storage format of database table 1o' National policy 4
Figure 5: Flowchart of normal update procedure Figure 5 (a) Flowchart of update procedure during backup work? -) No. 15
Figure (c) Database recovery manual flowchart ↑-Figure 5 (d)

Claims (1)

[Scope of Claims] In a database management system that stores pre-update images of database records stored in a secondary storage device and performs transaction failure recovery, when updating database records stored in the secondary storage device, An update transaction number is recorded in the record, and when a record is updated during backup, if the transaction number of the update request is different from the transaction number recorded in the record, the pre-update value of the record is saved in the pre-update value storage area and the backup data storage area. After that, a database update control unit updates the record;
When backing up the record stored in the secondary storage device, the database backup control unit selects which of the current value, pre-update value, and backup value of the record to back up based on the update transaction number recorded in the record. A database management system characterized by: