Patent Application
20190278781
The replication or mirroring of data changes from a source database to a target database can be performed either continuously or periodically according to a schedule. In a scheduled replication, a user specifies a point in a database log at which the replication is to end. The transactions at the source database logs are examined, and the net change between the last replication and the user-specified point is replicated to the target database tables. Optimization techniques exist that examine the end image of a database table row. However, these optimization techniques are limited to net changes within a single transaction.
Disclosed herein is a method for net change data replication across a plurality of transactions in a replication environment, and a computer program product and system as specified in the independent claims. Embodiments of the present invention are given in the dependent claims. Embodiments of the present invention can be freely combined with each other if they are not mutually exclusive.
According to an embodiment of the present invention, in optimizing net change data replication across a plurality of transactions in a replication environment, a source replication engine at a source database system: obtains a window in a source database log for the net change data replication; for a given row identifier found in the source database log, identifies an initial operation and a latest operation across the plurality of transactions within the window; compares the initial operation and the latest operation for the given row identifier to determine a net change to a row associated with the given row identifier; and stores the net change as a final operation on the given row identifier in an optimization repository for replication to a target database. The operations stored in the optimization repository are then sent to a target database system for replication to the target database.
In one aspect of the present invention, the window is a range of entries in the source database log from a previous net change data replication to a point in the source database log at which the net change data replication is to end.
In one aspect of the present invention, when each transaction of the plurality of transactions commit, each transaction is assigned a system change number (SCN). The initial operation is an operation in the source database log associated with the given row identifier and has a lowest SCN within the window. The latest operation is an operation in the source database log associated with the given row identifier and has a highest SCN within the window.
For example, assume that, for a given row identifier, 1000 UPDATE operations across multiple transactions were performed within the window, where a “salary” column value in a row with an “empid” column value=1 was changed. The initial operation is identified as the first UPDATE operation, and the latest operation is identified as the last UPDATE operation on the row (302). However, the last UPDATE operation sets the final salary value. The source replication engine 102 compares the initial and latest operations and determines that the net change is the value for the “salary” column as updated by the last operation (303). In this case, using the optimization process according to the present invention, only an UPDATE operation setting the final salary value is stored in the optimization repository 105 to be replicated to the target database 113 (305), avoiding the replication of the other 999 UPDATE operations.
For another example, assume that, for a given row identifier, an INSERT operation is performed in an initial operation within the window and a DELETE operation is performed in a latest operation within the window. The initial operation is identified as the INSERT operation, and the latest operation is identified as the DELETE operation (302). The source replication engine 102 compare the initial and the latest operations to determine that the net change is the deletion of the row associated with the given row identifier (303). Thus, neither operations is replicated to the target database 113 (304), avoiding the replication of both the INSERT and the DELETE operation, and any intervening operations, for the given row identifier within the same window.
When the initial operation is an UPDATE (401), the source replication engine 102 determines whether the initial UPDATE operation is in scope (402). If the initial UPDATE operation is not in scope, and the latest operation is a DELETE (407), then the net change is null, and there is no replication (412). If the initial UPDATE operation is not in scope (402), and the latest operation is an UPDATE (407) that is also not in scope (408), then the net change is null, and there is no replication (412). If the initial UPDATE operation is not in scope (402), and the latest UPDATE operation is in scope (408), then the net change is a match to the latest operation, and an INSERT with the latest operation data is stored in the optimization repository (409).
If the initial UPDATE operation is in scope (402), and the latest operation is a DELETE (403), then the net change is a DELETE, and a DELETE with the initial operation data is stored in the optimization repository (410). If the initial UPDATE operation is in scope (402) and the latest UPDATE operation is also in scope (403-404), then the source replication engine 102 determines whether the replication key has changed (405). If the replication key has not changed, then the net change is an update, and an UPDATE with the latest operation data is stored in the optimization repository (411). If the replication has changed (405), then to ensure that the old replication key is not replicated, a DELETE with the initial operation data and an INSERT with the latest operation data are stored in the optimization repository (406).
Embodiments of the present invention can significantly reduce the overall elapsed time for performing a net change replication. The embodiments can also significantly reduce the overall amount of data being replicated, hence reducing the workload of the entire replication pipeline from source to target. The embodiments can further increase the throughput of the net change replication. A configurable number of multiple threads may be used. By optimizing net change replication in the above described manner, the use of resources of the source replication engine 102, such as CPU cycles, memory, and disk space, may be optimized.
The present invention may be a system, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention.
The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.
Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers. A network adapter card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing/processing device.
Computer readable program instructions for carrying out operations of the present invention may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like, and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention.
Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions.
These computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram block or blocks.
The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks.
The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.
The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15803170 | Nov 2017 | US |
| Child | 16421481 | US |
