JP4289056B2 - Data duplication control method between computer systems - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a business system including a computer and a storage device, and more particularly to a data duplication control method for replicating data between a plurality of systems and a method for realizing high-speed switching to a system that replicates data.
[0002]
[Prior art]
As a data replication method when there are a plurality of business systems including a database server and a storage device, there is a method executed by a DBMS operating on the database server. For example, Non-Patent Document 1 describes how the DBMS replicates data. This is a technology for replicating data by connecting database servers of a plurality of systems and transferring update information of a DBMS operating on one system to another system.
[0003]
As a similar system data duplication method, there is a method of using a data copy function between storage apparatuses. The data copy function between storage apparatuses is described in Non-Patent Document 2, for example. This is a technology in which storages of multiple systems are connected by a fiber channel, and when the disk drive of one storage device is updated, the data update is reflected to the disk drive of another storage device.
[Non-Patent Document 1]
Oracle9i product catalog (https://www.oracle.co.jp/products/catalog/pdf/9iDBr2J07266-01.pdf), page 6.
[Non-Patent Document 2]
Hitachi Integrated Storage Solution “Storeplaza” catalog (hppt: //www.hitachi.co.jp/Prod/comp/storeplaza/data/stpzclg.pdf), page 5.
[0004]
[Problems to be solved by the invention]
When the conventional data replication method is executed, a cost higher than that for performing a normal database operation is required. In addition, when data replication is synchronized between a plurality of systems, a delay in business processing occurs.
[0005]
In order to perform data replication by DBMS, a database server on which the DBMS operates adds a load for performing data processing in addition to a load for performing business processing, so a higher-performance database server is required and costs increase. There are challenges. Further, in order for the replicated data to match, it is necessary to perform synchronous communication between the database servers every time the DBMS update process is executed. During the synchronous communication, the DBMS cannot execute the next update process, so that the task is delayed.
[0006]
In order to perform data replication in the storage apparatus, it is necessary to use a broadband line for connection between the storage apparatuses in order to copy all data updates handled by the DBMS. There is a problem that the cost is increased by using a broadband line. Further, in order for the replicated data to match, it is necessary to perform synchronous communication between the storage apparatuses every time the data on the disk drive is updated. During synchronous communication, the next update process to the disk drive cannot be executed, so the task is delayed.
[0007]
In addition, there is a method to execute communication between DBMS and storage device asynchronously to prevent delay due to synchronous communication. However, when switching to a data replication destination system due to a failure or disaster, untransferred data is copied to the replication destination. Therefore, it is necessary to rebuild the system, and the problem is that the system switching is delayed.
[0008]
[Means for Solving the Problems]
When a server executes a job in response to a request received from the outside, it is necessary to update or add to data stored in the storage device. Rather than copying all data to perform data replication on this storage device, prepare a server and storage device as the replication destination, and specify the storage device log that can restore the work performed on the replication source server The disk drive is copied to the duplication destination storage device every time the disk drive is updated. When copying of the disk drive to the replication destination storage apparatus is completed, the replication destination server is notified that the disk drive storing the log is updated from the copied storage apparatus. The copy destination server should be able to receive the change notification of the disk drive that saved the log from the storage device. After receiving the notification, the log is read from the disk drive and is the same as that performed on the copy source server. Execute business processing. After execution of the business process based on this log, the result is reflected in the storage device to complete the data replication.
[0009]
In a system running this data replication method, if the replication source server and storage device are stopped due to a failure or maintenance operation, the business data stored in the replication destination storage device is up to date, so the replication source By changing the transaction received by the server to be received at the replication destination, switching between the server and the storage device is executed without stopping the transaction processing.
[0010]
After switching between the server and the storage device, the system that received and processed the work was stopped by replacing the processing that was executed for data replication by both the replication source server and the storage device. In this case, the server and the storage device are switched again.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the embodiment described below, a database server is taken as an example of a task that runs on a computer, but the task that is executed on a computer is not limited to a database. The business that operates on the computer may be any one in which the data to be replicated is updated by the business performed in the primary system, and a log that can reproduce the update of the data in the secondary system is generated. For example, it can be implemented by a file system.
[First Embodiment]
FIG. 1 shows an embodiment of a data replication system using a database server and a storage apparatus to which the present invention is applied.
[0012]
The database server 2 and the storage device 8 constitute the primary system. The storage connection device 3 built in the database server 2 and the disk control device 5 of the storage device 8 are connected by a server / storage connection interface 4. The storage device 8 has built-in disk drives 6 and 7 for storing data to be read and written by the disk control device 5, and the database server 2 receives and processes the business request through the business network 1 and is necessary for the processing. Data and business data executed in the database server 2 are held.
[0013]
The database server 2 and the storage device 8 not only read and write data through the server-storage connection interface 4, but also when the disk drives 6 and 7 requested by the database server 2 are changed, the storage device 8 The database server 2 is notified.
[0014]
The database server 12 and the storage device 18 constitute the secondary system. The storage connection device 13 built in the database server 12 and the disk control device 15 of the storage device 18 are connected by a server-storage connection interface 14. The storage device 18 has built-in disk drives 16 and 17 for storing data to be read and written by the disk controller 15, and the database server 12 receives and processes the business request through the business network 1 and is necessary for the processing. Data and business data executed in the database server 12 are held.
18 indicates not only reading / writing of data through the server / storage connection interface 14 but also notification from the storage device 18 to the database server 12 when there is a change in the disk drives 16, 17 requested by the database server 12. Have a way to do.
[0015]
The disk control device 5 and the disk control device 15 are connected by an inter-storage device connection interface 20. As a result, the storage device 8 of the primary system and the storage device 18 of the secondary system are connected to each other. The storage device 8 and the storage device 18 copy the contents through the inter-storage device connection interface 20 by setting one of the disk drives as a copy source and the other disk drive as a copy destination in advance. Have a way to do.
[0016]
Hereinafter, operations of the data replication method and the system switching method of the present embodiment will be described. In this embodiment, data replication is performed between a primary system that normally executes business and a secondary system that takes over the business when the primary system becomes inoperable for some reason.
[0017]
First, initial setting for realizing the data replication method is performed for both the primary system and the secondary system.
[0018]
The initial setting of the primary system starts with building a database according to the business system. In the disk control device 5 of the storage device 8, the disk drives 6 and 7 usable by the database server 2 are allocated. The database server 2 sets a disk drive 6 that holds database data and a disk drive 7 that holds a database log. The log referred to here represents a database update operation step by step, and the database can be reconstructed by re-executing the log. For example, a transaction log executed by the database or an SQL command for all business requests received by the database server. A transaction is a processing unit in which a plurality of database processes are combined, and all the processes succeed or fail. For this reason, a business system that must process a large number of business requests is used in order to prevent inconsistencies in the database by performing processing in units of transactions.
[0019]
A database similar to the primary system is constructed in the secondary system. In the storage device 18, a disk drive 16 similar to the disk drive 6 that can be used by the database server 2 in the storage device 8 and a disk drive 17 similar to the disk drive 7 can be used by the database server 12 in the disk control device 15. Assign as follows. Similar to the database server 2, the database server 12 sets a disk drive 16 that holds database data and a disk drive 17 that holds a database log.
[0020]
Next, a setting is made so that the disk drive 7 holding the database log is copied to the disk drive 17 through the inter-storage apparatus connection interface 20 between the storage system 8 of the primary system and the storage apparatus 18 of the secondary system. This disk drive copy can be either a synchronous copy or an asynchronous copy. For example, in the case of synchronous copy, in response to an information write request from the database server 2 to the disk drive 7, both the information write to the disk drive 7 and the information write to the disk drive 17 are completed, and then the database server 2 indicates a write completion report. On the other hand, the asynchronous copy differs from the synchronous copy in that a write completion report is sent to the database server 2 when the information write to the disk drive 7 is completed. When performing asynchronous copy, the log disks of the primary system and the secondary system do not always match, and data may be lost when the system is switched.
[0021]
Then, the database server 12 of the secondary system is set to notify the database server 12 when the disk drive 17 is updated to the disk controller 15 of the storage device 18.
[0022]
When a failure or disaster occurs in the primary system, it is necessary to quickly detect the stop of the primary system in order to switch to the secondary system. Therefore, a communication setting for notifying that the primary system is operating is performed between the primary system database server 2 and the secondary database server 12. For example, there is a method in which the database server 2 of the primary system notifies the database server 12 of the secondary system via the business network 1 at regular time intervals. There are also a method for instructing switching from an external server that monitors the operating status of the primary system to the secondary system, and a method for inquiring the operating status from the secondary system to the primary system at regular time intervals.
[0023]
After the setting as described above is completed in the database servers 2 and 12 and the storage devices 8 and 18, business processing is started in the database server 2 of the primary system. In the following, the data replication procedure will be described.
[0024]
Data replication first step 101: The business processing request arrives at the database server 2 through the business network 1. The business processing request is sent according to a protocol on the business network, and includes a request for referring to or updating data contents managed by the database server 2. For example, it consists of a combination of SQL commands sent by the TCP / IP protocol.
[0025]
Upon receiving the business process request, the database server 2 analyzes the network protocol layer, extracts the business process contents from the database, analyzes the business process contents, and then executes the business process. For example, there is a process of analyzing a TCP / IP protocol, extracting an SQL command, and executing the process on a database.
[0026]
Data replication second step 102: When the contents of the business process involve database update processing, it is necessary to update the data held in the storage apparatus. In this case, the storage apparatus connection apparatus 3 instructs the storage apparatus 8 to write the update log to the disk drive 7 to the disk control apparatus 5 through the server / storage connection interface 4. For example, a host bus adapter is attached to the database server 2 and a SCSI command is transmitted to the disk controller through a fiber channel cable. This update log writing is not always executed every time data is updated, but also when the execution is completed in units of transactions, when the log buffer prepared in the database server 2 runs out, or for a certain period of time. It is also possible to use a method of executing according to the condition in the unit of input / output designated by the database server 2 such as after the elapse of time. Further, in the present embodiment, for the sake of simplicity, it is illustrated as a single write request, but normally a write request to another disk drive is divided into a plurality of requests and transmitted.
[0027]
Data replication third step 103: Upon receiving the update log write request, the disk controller 5 writes information to the disk drive 7.
[0028]
Data replication fourth step 104: Since the disk drive 7 is set to be copied to the disk drive 17 in the storage apparatus 18 of the secondary system when the writing of the information is completed, the disk control apparatus 5 is connected to the inter-storage apparatus connection interface. 20, the update contents of the disk drive 7 are transmitted to the disk controller 15 in the storage system 18 of the secondary system, and the disk drive 17 is instructed to write, and the disk controller 15 writes to the disk drive 17. When the writing is completed, the disk controller 5 reports the update log writing completion to the database server 2. For example, this can be realized by using a fiber channel cable as the inter-storage device connection interface 20 and setting a copy of the disk drives 7 and 17 with the storage device management software. Further, in this embodiment, the synchronous copy method for copying to the disk drive 17 immediately after the update of the disk drive 7 is used, but it is also possible to use an asynchronous copy method for executing copy at regular time intervals. However, when the asynchronous copy method is used, even if writing to the disk drive 17 is not completed, a completion report is sent to the database server 2 when writing to the disk drive 7 in the storage device 8 is completed. There may be situations where the drive data is not copied.
[0029]
Data replication fifth step 105: Upon receiving the update log writing completion report, the database server 2 instructs the disk control device 5 to write update data to the disk drive 6, and the disk control device 5 Write processing.
[0030]
Data replication sixth step 106: After the update to the disk drive 17 is executed, the disk controller 15 is designated in advance to notify the database server 12 of the update, so the database server 12 is notified that the update has occurred. To do. The interface between the update notification request and the update notification is, for example, a method in which the disk control device 15 notifies the database server 12 as a response to a read request from the database server 12 to a special disk drive in the storage device 18, or an update notification from the database server 12. A method of notifying the disk controller 15 as a response to the dedicated command to the requested disk drive 17, and a dedicated interrupt interface for notifying disk update from the disk controller 15 are provided in the storage connection device 13 in the database server 12. There are methods. The notification from the disk controller 15 to the database server 12 is not limited to a method that is executed every time an update occurs, but a method of notifying at regular time intervals or an instruction from the database server 2 to the storage device 8. There is a method of notifying the database server 12 of the information issued to the storage device 18 and executing the notification.
[0031]
Data replication seventh step 107: Upon receiving the update notification of the disk drive 17, the database server 12 reads information on the update of the disk drive 17 and stores the data on the disk drive 16 according to the update log. The connection device 13 notifies the disk control device 15 of an information write request through the server-storage connection interface 14. For example, there is a method of attaching a host bus adapter to the database server 12 and transmitting a SCSI command to the disk controller through a fiber channel cable.
[0032]
Each time the primary system database server 2 executes a business processing request, the primary system data is replicated to the secondary system in this way, so that the primary system database server 12 is not subjected to a load for data replication. Further, without transmitting data for data replication on the business network 1, the data transfer amount between the storage apparatuses 8 and 18 can be reduced, the cost of data replication can be reduced, and the business delay can be reduced. .
[0033]
When the primary system stops due to a disaster or equipment failure, the business process is switched to the secondary system. Even when it is necessary to perform maintenance work on the primary system, the primary system may be stopped and the business processing may be switched to the secondary system. FIG. 2 shows a procedure in which the secondary system takes over the business process after the primary system stops. The apparatus configuration is the same as that shown in FIG. In the following, a procedure for taking over business processing will be described.
[0034]
When the primary system stops, the system is switched and business processing is taken over by the database server 12 and the storage device 18 of the secondary system. The main system is stopped by, for example, heartbeat communication that performs communication between the database server 2 and the database server 12 at regular time intervals, or heartbeat communication by connecting a monitoring server other than the database servers 2 and 12 to the business network 1. It is detectable by the method of performing. The business process can be taken over by changing the setting so that the database server 12 can receive the business process request received by the database server 2. For example, there is a method of taking over the network address used by the database server 2 for receiving a business request.
[0035]
System switching first step 201: First, the storage server 18 is instructed to stop writing information from the disk drive 7 to the disk drive 17 from the database server 12, and then the disk on which the database server 12 has written the log. With reference to the drive 17, it is confirmed whether an unexecuted transaction exists in the disk drive 17. The reason for stopping the writing from the disk drive 7 to the disk drive 17 is unknown whether the database server 2 is operating normally and it is not clear whether the writing to the disk drive 7 is normally performed. This is because such a writing is not reflected in.
[0036]
System switching second step 202: If there is an unexecuted business process, the information is transferred from the storage connection device 13 to the disk control device 15 through the server-storage connection interface 14 so as to execute the business and update the data of the disk drive 16. Notify the write request. However, if log writing from the database server 2 of the primary system to the disk drive 7 is not performed in units of transactions, the log on the disk drive 17 may be interrupted during the transaction. In such a case, the data update for canceling the data update by the transaction in which the database server 12 is interrupted is necessary.
[0037]
System switching third step 203: The disk controller 15 writes the requested information to the disk drive 16.
[0038]
System switching fourth step 204: When the writing of information in the disk drive 16 is completed, the database server 12 receives a business request and starts business processing.
[0039]
In addition, when the primary system recovers from a failure / disaster and becomes operational again, or when the primary system becomes operational after maintenance work is completed, the data replication method described in this embodiment can be By applying it in the direction of copying to the system, it is possible to reflect to the primary system data and log updates due to business processing executed on the secondary system while the primary system is stopped.
[0040]
For example, the setting of copying the updated part of the disk drive 17 to the disk drive 7 between the storage apparatuses 8 and 18 is performed, and the database server 2 updates the data of the disk drive 6 according to the update log of the disk drive 7. Subsystem data replication is possible. As described above, if the primary system and the secondary system do not stop at the same time, the operation stop time can be reduced by alternately applying the data replication method of the present invention.
[0041]
In the present embodiment, the primary system and the secondary system have been described as having a one-to-one configuration. However, a method of replicating data from the primary system to a plurality of secondary systems, and data copied from the primary system to the secondary system are further different. A method of replicating data to the secondary system can be easily constructed.
[0042]
FIGS. 3 to 6 are flowcharts showing processing procedures of the database server and the storage apparatus, which are the main components of this embodiment. The flowchart of each figure is demonstrated below.
[0043]
A flowchart of the main system database server processing procedure shown in FIG. 3 will be described.
[0044]
First, initial setting of the database server is performed (301). For example, initial settings include database construction and disk drive allocation.
[0045]
Next, until the data replication system is constructed, it waits for the initialization of the storage apparatus and the secondary system to be completed (302). For example, it waits for the completion of the disk copy setting between the storage devices and the database construction of the secondary system.
[0046]
When the initial setting of the data replication system is completed, business process request acceptance is started (303). For example, merchandise management for business transactions performed via the Internet corresponds to business processing.
[0047]
It is determined whether the business process request has arrived after the business process request has been received (304).
If a business process request has arrived, the business process is executed (305). If the business process request has not arrived, the system waits for the business process request and continues to determine the arrival of the business process request. When a business process request arrives and the business process involves data update, a business process log is written in the storage device (306). Then, a log writing completion report is received (307). Thereafter, a data update request is sent to the storage apparatus (308).
[0048]
With respect to a data update write request made to the storage apparatus, the business process request is completed by receiving a write completion report from the storage apparatus (310).
[0049]
Once the primary system is operating, as described herein, the execution of the business process request and the accompanying log update and data update are repeated.
[0050]
The flowchart of the secondary system database server processing procedure shown in FIG. 4 will be described.
[0051]
Since the purpose of data replication is to execute business processing by switching after the primary system is stopped, the database server of the secondary system is initialized according to the settings of the primary system (401). For example, preparation of a log disk or a data disk to be copied is necessary for data replication.
[0052]
Next, in order to refer to the log copied from the primary system, a setting is made to detect the log disk update of the storage device (402). For example, a method for specifying that a log disk update should be notified from the database server of the secondary system to the storage system of the secondary system, or a log disk in the storage device is periodically read from the database server of the secondary system. A method of determining whether or not is possible. As a result, log updates can be detected.
[0053]
Then, when the log is updated, data replication processing is started in which the contents are executed by the secondary system to update the database data (403).
[0054]
In order to determine whether system switching is necessary, it is determined whether the primary system is operating normally (404). For example, switch the system when there is no operation status notification from the primary system to the secondary system for 10 seconds, or connect an operational status monitoring server other than the primary and secondary system database servers to the business network to monitor the status. Therefore, if it is determined that the primary system is not operating, a policy is determined so that the secondary system takes over the business processing, and the determination is executed. A plurality of methods for determining the operating state of the primary system can be considered in this way, and the method is not limited to the method shown here.
[0055]
If it is determined that the main system is not operating normally, system switching processing is performed. First, the business takeover process of the primary system is executed (410), so that it can be connected to the business network, and then the unexecuted business process is executed with the updated log disk (411). As a result of the execution, data update is sent to the storage device (412). By receiving the data update completion report of the storage apparatus (413), it is considered that the data replication of the primary system has been completed. When all the unexecuted business process data in the log disk is reflected in the storage device, the business process request acceptance is started (414).
[0056]
If it is determined that the operating state is normal, it is determined whether an update of the log disk has been detected from the storage device (405). The method of detecting the update of the log disk is a method of generating an interrupt from the storage device to the database server, a method of returning a response to a special I / O command issued from the database server to the storage device, or a time when the database server is in a certain period of time. There is a method of reading the contents of the log disk at intervals and analyzing the information. When the update of the log disk is detected, the updated part of the log disk is read (406). Then, the data update is executed by applying the log update (407). Further, the data update generated by the data update execution is sent to the storage apparatus (408) so that the data matches the latest one of the primary system. When a data update completion report of the storage device is received (409), preparations for system switching are made while data copy is repeated by repeatedly receiving the status notification and waiting for the storage device update notification.
[0057]
A flowchart of the processing procedure of the primary system storage apparatus shown in FIG. 5 will be described.
[0058]
First, initialization is performed such as assigning a disk drive in the storage apparatus to the database server (501).
[0059]
Then, in order to perform the data replication method of the present embodiment, the log disk of the primary system is associated with the log disk of the secondary system, and a copy setting is made (502). Before performing this setting, it is necessary to complete the initial setting of the database server and storage device of the secondary system.
[0060]
When the setting is completed, read / write processing is started (503), and a data update request from the database server is accepted.
[0061]
When a request is received from a state waiting for reception of a processing request (504), it is first determined whether it is a write request (505). If it is not a write request, the requested information is transferred to the database server (511), and an information read completion report is transmitted to the database server (512). Actually, it receives a request for controlling the disk drive, etc., but here it is regarded as the same as a read request. When a write request is received, the requested information is written to the disk (506), and it is determined whether the disk is a disk for which copying has been set (507). If copying is not set, a data write completion report is transmitted to the database server (510). If the disk is a copy set, the write request and information are transferred to the storage system of the secondary system (508), and a write completion report is awaited from the storage system of the secondary system (509). When a completion report is received from the secondary system, an information write completion report is transmitted to the database server (510). Here, a method of performing synchronous copy between the storage system of the primary system and the secondary system is used.
[0062]
In this way, the storage system of the primary system waits for a processing request from the database server, and repeats disk information reading / writing processing and disk copying processing to the secondary system.
[0063]
A flowchart of the secondary system storage apparatus processing procedure shown in FIG. 6 will be described.
[0064]
First, initial settings such as allocation of disk drives in the storage apparatus to the database server and disk copy settings from the external storage apparatus are performed (601).
[0065]
Then, after the read / write processing is started (602), a request from the database server can be received. Furthermore, the disk for update notification is designated from the database server (603), and preparation for data replication is completed.
[0066]
Processing request reception (604) is started, and when a processing request is received, it is determined whether the request is a write request (605). If it is not a write request, the information requested to be read is transferred to the request source (610), and an information transfer completion report is transmitted to the request source (611), thereby completing the execution of the processing request. On the other hand, if it is a write request, first, the requested information is written to the disk (606). Then, an information writing completion report is transmitted to the request source (607). This completes the processing of normal processing requests. However, if writing to a disk occurs to implement the data replication method, it is determined whether the disk is a disk for which an update notification is specified by the database server (608). If it is the designated disk, the update is notified to the database server (609). If not specified, the process is completed without notification.
[0067]
In this way, the storage system of the secondary system processes the log disk write from the primary system and the read / write request from the database server of the secondary system, and repeats the process of sending the notification if the disk notifies the update. Realize data replication process.
[0068]
Although switching from the primary system to the secondary system as in the present embodiment, using the data replication method as described above, especially when the disk copy between the storage apparatuses 8 and 18 is performed by the synchronous copy method, a log required for data replication is leaked. Therefore, the delay associated with system switching can be reduced.
[Second Embodiment]
In the first embodiment, an interface other than normal disk drive read / write is required to notify the database server of disk drive updates. However, in the second embodiment described below, only the disk drive read / write interface is required. To achieve data replication. The configuration of the data replication system is the same as that of the first embodiment shown in FIG.
[0069]
In the first embodiment, the setting for notifying the database server 12 of the update of the disk drive 17 in the secondary system is performed. On the other hand, in this embodiment, the disk drive 17 is monitored from the database server 12 by polling to detect an update.
[0070]
The update can be detected by the following procedure. The database server 12 holds the position where the log is written in the disk drive 17, and periodically reads the data at that position to determine whether it has been updated. If it has been updated, the database server 12 performs business processing according to the log. When the process is completed, the position where the log is written is updated, and the determination process is repeated to read periodically and update it.
[0071]
The database update log is usually written to the disk so that it is not overwritten sequentially in a certain area. Then, when writing is performed up to the end of the area, data is sequentially written again from the beginning of the area. Therefore, if it is guaranteed that the contents can be read by the database server before the update log write is overwritten, and that the update log can be distinguished one by one, it is monitored by polling. Data can be duplicated by updating the data disk drive.
[0072]
As described above, when data replication is performed by monitoring the update of the disk drive from the database server by the polling, the delay due to the system switching can be reduced by sufficiently reducing the polling interval. Further, the system configuration is the same as that of the first embodiment, and the cost for data replication can be reduced. Furthermore, if the disk copy between the storage apparatuses 8 and 18 is performed by the synchronous copy method, the log required for data replication can be copied without omission, and therefore the delay associated with system switching can be reduced.
[Third Embodiment]
In the first embodiment and the second embodiment, it is assumed that the database servers 2 and 12 and the storage apparatuses 8 and 18 are directly connected or connected via a storage area network. However, in this embodiment, the storage apparatus This is realized using a network attached storage (NAS) device. The configuration of the data replication system of this embodiment is the same as that of the first embodiment shown in FIG.
[0073]
In this embodiment, the disk copy method between storage apparatuses is different from the first embodiment and the second embodiment. The NAS device receives an access request in the file system. Therefore, the inter-storage connection interface between the disk control devices 5 and 15 also performs access in units of files. Therefore, it is necessary to detect the update of the log file operated by the database server 2 instead of detecting the change of the disk drive 7 in the disk controller 5. To detect the update, the disk controller 5 executes a daemon for periodically monitoring the update of the log file, and when the update occurs, a copy of the file is written to the disk drive 17 through the inter-storage connection interface. Also, the interface for notifying the log update in the secondary system is different from those in the first and second embodiments. The disk controller 15 includes a daemon that detects log file updates. A process for communicating with the daemon is generated in the database server 12, that is, a mechanism for notifying when a log file is updated is constructed. Alternatively, the method of monitoring by polling from the database server 12 shown in the second embodiment may be applied to the log file.
[0074]
Further, as a method for copying log data, a method of providing a disk control device capable of detecting changes in units of disk drives different from the disk control device 5 in the storage devices 8 and 18 and updating the disk between them is also possible. In this case, data copy from the disk drive 7 to the disk drive 17 is executed by a separately provided disk control device as in the first embodiment. The method of notifying the database server 12 of the update of the log data is possible by a method of communicating with the daemon of the disk control device 15 as described above in the process of the database server 12 or a method of monitoring from the database server 12 by polling.
[0075]
Further, when copying log files in the NAS device, it is necessary to transfer all the files between the storage devices 8 and 18. In order to reduce the data transfer amount, it is possible to reduce the transfer amount of update logs by creating a directory for storing logs and placing update logs as files one by one in the directory. The database writes the date and time when the update log was created using the file name. This allows for unique identification of the log. In addition, by deleting logs that have exceeded a certain period of time, log duplication can be guaranteed and the disk drive will not be exhausted. The log data update is notified to the database server 12 in the same manner as described above, but the daemon that monitors the log update executed by the disk controller 15 monitors the file under the log directory and creates a new log file. Is created, the process of the database server 12 is notified. When the database server 12 executes a daemon for monitoring file updates by polling, it similarly monitors whether a new file has been created under the log directory.
[0076]
By constructing the system in this way, data replication is realized. The system configuration is the same as that of the first embodiment, and the cost can be reduced. In addition, the delay at the time of system switching can be reduced.
[Fourth Embodiment]
FIG. 7 shows an embodiment of a data replication system using a database server and a storage apparatus to which the present invention is applied and software operating on them. In this embodiment, the application program that runs on the server is a DBMS, but the present invention can be applied to any program that outputs data updates as a log. For example, a transaction monitor may be used.
[0077]
The configuration of the data replication system is the same as that of the first embodiment shown in FIG. 1, but the storage connection devices 3 and 13 on the database servers 2 and 12 are omitted in FIG. On the database servers 2 and 12, OSs 72 and 75 and DBMSs 71 and 74 operate, respectively. The OSs 72 and 75 are executed as an operating environment for hardware control of the databases 2 and 12 and other application programs. The DBMSs 71 and 74 are application programs that execute system tasks. Further, on the disk control devices 5 and 15 on the storage devices 8 and 18, control software 73 and 76 for receiving requests from the database servers 2 and 12 and updating the disk drives 6, 7, 16 and 17 operate. The processing performed through the storage connection devices 3 and 13 in the first embodiment is assumed to be processed internally from the DBMSs 71 and 74 by the functions of the OSs 72 and 75.
[0078]
In the present embodiment, data replication is realized by the system configuration similar to that of the second embodiment, using each device and software operating on these devices. That is, there is no interface for notifying that the information of the disk drives 16 and 17 has been changed from the storage device 18 to the database server 12.
[0079]
The OS 72 operating on the database server 2 constituting the primary system can execute an operation of writing information to the disk drives 6 and 7 in the storage apparatus 8 or reading the information. The control software 73 performs processing such as reflecting information to the disk drives 6 and 7 and transferring information to the OS 72 in response to a request from the OS 72 sent through the server-storage connection interface 4. The DBMS 71 operates on the OS 72 and performs system operations. The secondary system is configured so that the database server 12 and the storage device 18, and the OS 75, DBMS 74, and control software 76 operating on these can perform the same processing as the primary system.
[0080]
Between the control software 73 and 76, the contents of the disk drives held by each other can be transferred through the inter-storage connection interface 20, and the information can be reflected in the designated disk drive. For example, this can be realized by using remote copy or synchronous remote copy between storage apparatuses.
[0081]
First, initial setting of the primary system and the secondary system is performed. The disk drives 6 and 7 in the storage apparatus 8 recognized by the OS 72 in the primary system are allocated to the data disk and log disk of the DBMS 71. In the secondary system, the DBMS 74 allocates the disk drive 16 in the storage device 18 recognized by the OS 75 to the data disk and the disk drive 17 to the log disk in accordance with the disk configuration of the primary system. Further, the operating states of the DBMS 71 and the DBMS 74 are checked. This is because when the primary system is stopped, the secondary system operation is quickly taken over.
[0082]
The initial setting between the storage devices 8 and 18 is to copy the information change of the disk drive 7 to the disk drive 17. As a result, the log of the process executed by the DBMS 71 is copied to the secondary system so that it can be referenced from the DBMS 74. This copying method can be either synchronous or asynchronous. However, in the case of asynchronous, there is no guarantee that all logs up to the point when the primary system stops can be transferred. On the other hand, in the case of synchronization, the log until the primary system stops can be completely referred to by the secondary system, and high-speed and accurate data replication is possible.
[0083]
When the setting up to here is completed, data replication from the primary system to the secondary system is possible by executing the procedure described below. Therefore, work is started on the main system. The DBMS 71 accepts and processes a business process request from the business network 1. The log that can be reproduced in sequence at this time is a log, and the DBMS 71 requests the control software 73 to write to the disk drive 7 via the function of the OS 72 (702). However, the business process request is not only received from the business network, but the process executed on the database server 2 for database construction and maintenance is also included in the business process request. In order to perform complete data replication, it is necessary to create a log for all these business process requests and write them to the disk drive 7.
[0084]
As a unit in which the DBMS 71 requests the disk drive 7 to write a log, for example, there is a method in which a transaction is committed. Alternatively, there is a method of requesting the disk drive 7 to write the contents of the log buffer possessed by the DBMS 71 when the log buffer possessed by the DBMS 71 is full or when a certain time has elapsed. In any case, in order for the work log executed by the DBMS 71 to be replicated without being lost in the DBMS 74 of the secondary system and without inconsistency between the data managed by the DBMSs 71 and 74, the DBMS 71 must be a disk drive. 7 is required to synchronize the information between the disk drive 7 and the disk drive 17 in the unit requested. In the following, it is assumed that the information on the disk drive 7 and the information on the disk drive 17 are synchronized. However, it is not always necessary to synchronize, and copying from the disk drive 7 to the disk drive 17 may be performed asynchronously. However, when asynchronous copying is performed, it is not guaranteed that the logs of the primary system and the secondary system match, and data handled by the DBMS 71 and DBMS 74 may be inconsistent when switching from the primary system to the secondary system. It may be necessary to check and correct data contents between subsystems.
[0085]
Upon receiving the request, the control software 73 writes the request to the log disk drive 7 (703). Since this disk drive 7 is specified to be copied to the disk drive 17 of the storage device 18 by default, the control software 73 transfers the write request for the change to the control software 76 through the inter-storage device connection interface 20, The received control software 76 writes the requested information into the disk drive 17 (704). Here, in order to perform synchronous copying between the disk drive 7 and the disk drive 17, a completion report is sent to the database server 2 after the information writing to the disk drive 17 is completed, and after receiving the report, the DBMS 71. Need to continue the business process. As a result, the business log executed by the DBMS 71 matches the log copied to the secondary system. On the other hand, when writing to the disk drive 7 is completed, a writing completion report is sent to the database server 2, and if copying to the disk drive 17 is performed at an arbitrary time unrelated to the request from the DBMS 71, asynchronous copying results in the secondary system. It is possible that the log being referenced does not match that of the primary system.
[0086]
Further, the DBMS 71 sends the data change caused by the business process to the control software 73 through the function of the OS 72 (704). Then, the control software 73 performs the requested information writing process and reading process on the disk drive 6 (705). However, the order of the log write request from the DBMS 71 to the disk drive 7 and the data write request to the disk drive 6 is not determined. Data writing includes a method of periodically requesting data stored in the data buffer on the OS 72 and a method of writing data when it is not used in business processing for a certain period of time. In order to follow the work executed by the primary system, the log of the executed process must be transferred to the secondary system, but the data need only be consistent within the scope used by the primary system for work. .
[0087]
On the other hand, the DBMS 74 of the secondary system issues a request to the control software 76 using the function of the OS 75 (706), and reads the information as to whether the information of the disk drive 17 has been changed (707). As a result, if there is a change in the log contents on the disk drive 17, an information update request is issued to the control software 76 in order to execute the work of the log and update the data in the disk drive 16 of the secondary system (708). . Upon receiving this request, the control software 76 reflects the contents of the information change on the disk drive 16 (709). These processes are performed at regular intervals, the log process is executed to update the data, and the primary system data is replicated to the secondary system. Alternatively, as in the first embodiment, the storage controller 15 or the control software 76 is instructed from the server 12, and when the information of the disk drive 17 is updated, the log change is recognized by the interface that notifies the server 12 of the updated information. The method is also possible.
[0088]
There are a plurality of methods by which the DBMS 74 reads log changes from the disk drive 17, applies them to the data in the disk drive 16, and replicates the data. For example, if writing from the DBMS 71 to the disk drive 7 is performed in the unit in which the transaction is committed, the DBMS 74 may execute the log newly written in the disk drive 17 as it is. Further, when writing from the DBMS 71 to the disk drive 7 is executed regardless of the transaction commit, a method of executing the written log as it is, and a DBMS 74 securing it on the transaction management table, There is a method of reflecting the log in the management table to the data after receiving the transaction commit while holding the read log.
[0089]
If the DBMS 74 detects the stop of the DBMS 71 in the operation state monitoring performed between the DBMS 71 and the DBMS 74, the setting is changed so as to take over the work performed by the DBMS 71 (710). However, before the DBMS 74 takes over the business process, it is necessary to perform a process for guaranteeing consistency between the business data of the primary system and the data of the secondary system executed by the DBMS 71, that is, recovery. If log synchronization between the disk drive 7 and the disk drive 17 is performed in units of transaction commits, it is checked whether there is a log not yet executed in the secondary system in the disk drive 17, and if there is, processing of the log is executed. Then, an information update request is issued to the control software 76. (708) Then, the control software 76 updates the information on the disk drive 16 to the request (709). When the data update on the disk drive 16 is executed for all the unexecuted logs of the disk drive 17, the recovery is completed, and the server 74 receives the business process request from the business network 1 and the DBMS 74 starts the business process.
[0090]
The processing executed to guarantee the consistency of the business data before taking over the business processing between the systems, that is, the recovery is guaranteed that the log writing to the disk drive 17 is a commit unit, It differs from the case where it is not guaranteed. Here, the case where writing in a commit unit is not guaranteed includes, for example, the case where information before commit is written by checkpoint processing, or the case where information before commit is written because the buffer of the DBMS 71 overflows. Hereinafter, a recovery method will be described for each case where writing in a commit unit is not guaranteed.
[0091]
First, the recovery process when log writing in a commit unit is guaranteed will be described. When writing in commit units is guaranteed, all the logs written in the disk drive 17 may be reflected in the data. Therefore, recovery is realized by recognizing a log that has not been executed in the disk drive 17 and rolling forward the log. When using synchronous copy, it is guaranteed that all the information committed in the primary system has been copied to the secondary system, and the log copied by the recovery process can be applied without omission. It is guaranteed that there are no defects.
[0092]
When writing in a commit unit is not guaranteed, the disk drive 7 includes a committed transaction log and an uncommitted transaction log. Here, only committed transactions should guarantee consistency. This is because changes due to uncommitted processing are not reflected in the data of the primary system. Therefore, recovery is executed only for committed transactions and not executed transactions. As such a recovery method, the following three methods are conceivable.
[0093]
For example, after all the logs written in the disk drive 7 are rolled forward, an uncommitted amount is detected, and only a detected uncompleted transaction is rolled back. For example, there is a method of detecting uncommitted transactions by scanning the log from the end toward the top. Alternatively, the DBMS 74 prepares a table for managing the transaction state in advance (hereinafter referred to as a transaction management table), and before the stop of the DBMS 71 of the primary system is detected, log writing to the disk drive 17 is performed to perform roll forward. There is a way to change its state each time. In the latter case, an uncommitted transaction registered in the transaction management table may be rolled back at the time of recovery.
[0094]
Further, in the case where a log change is detected after the time point when the DBMS 71 of the main system is detected to be stopped, a method of performing the roll forward after investigating the state of the transaction before performing the roll forward is also conceivable. When roll forward of the committed transaction is completed, the uncommitted transaction is investigated before the time when the DBMS 71 is detected to be stopped, and if there is an uncommitted transaction, rollback is performed. The investigation of uncommitted transactions may be performed by scanning from the time when the DBMS 71 is detected to the end of the log or using information in the management table.
[0095]
Another possible method is to roll forward only transactions for which commit has been confirmed. For example, a method of rolling forward the transaction when the committed state is reached in the management table can be considered.
[0096]
As described above, using the three recovery methods when log writing in commit units is not guaranteed together with synchronous copy, it is guaranteed that the information written to the disk drive in the primary system has been copied to the secondary system, and the recovery The method ensures that committed transactions are rolled forward, so that there is no transaction loss in the system.
[0097]
In this way, by copying the business log executed on the primary system to the secondary system and restoring the business data from that log, the processing load on the primary system database server can be increased without increasing the processing load on the primary system. It is possible to copy data at low cost by suppressing the communication band for transferring information between the system and the sub system. In addition, when logs are transferred from the primary system to the secondary system by synchronous copy, data replication is completed without causing loss of business processing, and when the primary system must be stopped due to a failure or maintenance of the primary system, It is possible to switch the execution of business to the secondary system.
[0098]
【The invention's effect】
According to the present invention, it is possible to realize data replication between a plurality of systems including a database server and a storage device at a low cost and with a small delay in normal business. Further, the delay at the time of system switching can be reduced.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a data replication system comprising a primary system and a secondary system and a data replication method between the primary and secondary systems.
FIG. 2 is a conceptual diagram of a data replication system composed of a primary system and a secondary system and a system switching method between the primary and secondary systems.
FIG. 3 is a flowchart of a processing procedure performed by the database server of the primary system.
FIG. 4 is a flowchart of a processing procedure performed by the database server of the secondary system.
FIG. 5 is a flowchart of a processing procedure performed by the storage device of the primary system.
FIG. 6 is a flowchart of a processing procedure performed by the storage system of the secondary system.
FIG. 7 is a conceptual diagram of a data replication system composed of a primary system and a secondary system and a system switching method between the primary and secondary systems.
[Explanation of symbols]
1: business network, 2: database server of primary system, 3: storage connection device, 4: server-storage connection interface, 5: disk control device, 6: data disk drive, 7: log disk drive, 8: primary system Storage device, 12: secondary system database server, 13: storage connection device, 14: server-storage connection interface, 15: disk control device, 16: data disk drive, 17: log disk drive, 18: secondary system Storage device 20: A storage device connection interface.

Claims (9)

A primary system having a first computer system and a first storage system connected to the first computer system; a second computer system; and a second storage connected to the second computer system. A data duplex control method in a system comprising: a secondary system having a system; and at least the first and second storage systems are interconnected,
Registering a log capable of reproducing the update of data held by the first storage system by processing of the first computer system in a specific storage device in the first storage system;
Copying the log registered in the specific storage device of the first storage system to the specific storage device in the second storage system set for duplication of the log;
Updating the data held by the first storage system by the processing of the first computer system;
A step in which the second computer system detects that the content stored in the specific storage device in the second storage system has changed by the copying step;
A step in which the second computer system reads a change in content held in a specific storage device in the second storage system;
The second computer system reads the log and updates the copy of the data held in the second storage according to the log;
A data duplication control method comprising: The log that can reproduce the update of the data held by the first storage system by the processing of the first computer system is composed of one or a plurality of transactions and includes information for distinguishing the start and end of the transactions. 2. The data duplex control method according to claim 1 , wherein: The step of registering, in the specific storage device in the first storage system, a log that can reproduce the update of data held by the first storage system by the processing of the first computer system is performed by the first computer system. 2. The data duplication control method according to claim 1 , wherein the data duplication control method is performed in a specified log input / output unit. A step of registering a log capable of updating data held by the first storage system by processing of the first computer system in a specific storage device in the first storage system; the second of the first storage data duplication method according to claim 1, characterized in that the step of copying the log changes of the specific storage device in a synchronous system the particular storage device in the storage system. 2. The data duplication control method according to claim 1 , further comprising a step of detecting that the first computer system has stopped, and a step in which the second computer system takes over work from the first computer system. Characteristic data duplication control method. 2. The data duplication control method according to claim 1 , wherein the step of detecting that the first computer system has stopped, the step of the second computer system taking over work from the first computer system, and the second step. The computer system further comprises a step of reading the log of the specific storage device in the second storage system and updating the data according to the log. A first storage system connected to a first database server for constructing a database and having a storage area for storing data of the database and a storage area for storing an update log indicating an update history of the database; and a second database A second storage system connected to the server,
A second storage for storing data used by the first storage area and the second database server; Memory area,
A storage control unit that controls input / output of data to and from the first storage area and the second storage area,
The storage control unit
The update log is sent from the first database server via the first storage system. The receiving department to receive,
Storing the update log in the first storage area;
Notifying the second database server that it has been stored in the first storage area,
A reflection request for reflecting the update log stored in the first storage area to the second storage area is received from the second database server,
Reflecting the update log in the second storage area;
When the reflection is completed, the second storage system is configured to notify the second database server of a completion report indicating completion. A first storage system connected to a first database server for constructing a database and capable of communicating with a first storage system comprising a storage area for storing data of the database and a storage area for storing an update log indicating an update history of the database A second database server connected to a second storage system comprising a storage area and a second storage area,
Detecting means for detecting whether or not a new update log is stored in the one storage area transmitted from the first storage system;
If detected by the detection means, read the update log from the first storage area. Taking out means,
Update request transmitting means for transmitting an update request for updating the read update log to the second storage area to the second storage system;
Means for receiving the update completion indicating completion of the update process corresponding to the update request from the second storage system. The second database server according to claim 8, wherein
If a failure of the first database server is detected,
Stop instruction means for instructing the second storage system to stop storing the update log in the first storage area;
Confirmation means for reading an update log from the first storage area and confirming whether there is an update log not reflected in the second storage area;
An update instruction means for instructing the second storage system to reflect in the second storage area when there is an unreflected update log;
When the update instruction means receives a reflection completion report from the second storage system, the second database server takes over the processing of the first database server in the second database server. .

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