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Bài giảng Cơ sở dữ liệu nâng cao - Chapter 6: Data replication

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Bài giảng Cơ sở dữ liệu nâng cao - Chapter 6: Data replication. Những nội dung chính được trình bày trong chương này gồm có: Overview of replication, replication scenario, replication types. Mời các bạn cùng tham khảo.

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Nội dung Text: Bài giảng Cơ sở dữ liệu nâng cao - Chapter 6: Data replication

Data Replication
Overview of Replication SQL Server replication is a set of technologies for: copying and distributing data and database objects from one database to another. Then, synchronizing between databases to maintain consistency. Types of replication: Snapshot replication. Transactional replication Merge replication Peer – to – peer replication Oracle Publishing replication All of these types rely on a number of standalone programs – agents.
Replication Scenario Replication is analogous to the publishing industry Article: a database object that you want to replicate; it can be a Table, View, or Store procedure, or other objects. Publication: A collection of articles. One article can be in one or more publications. Publication can be treated as a logical grouping for the articles For example: To replicate only the employee master data, you can include employee table article, address article, and any other relevant views to the publication
Replication Scenario Subscription: A request for a copy from the publication. Define where to receive the publication, what the frequency for the receiving is, … Publisher A database instance that holds publications for other database instances to receive. There can be several different types of publication in one publisher.
Replication Scenario Distributor: Each publisher has a distributor to store replication status data, and metadata about the publication. Sometimes the distributor acts as a data queue for data moving from the publisher to the subscribers and vice versa. There are two types of distributors:  local and remote.  Local distributor is where the publisher and distributor are in one database server instance. Subscriber: A database instance that receives replicated data from the publisher. In some replication types the subscriber also passes data to the publisher.
Replication Types Snapshot: Distribute data as it appears in the publisher at a specific moment of time. Whenever the Subscriber called for subscription, it will send the snapshot of the current Publisher and send it to the Subscribers. Limitations for using Snapshot Replication:  Replicating a small volume of data.  Infrequently changing data  Snapshot replication does not require primary article tables
Replication Types Components in Snapshot Replication: Two agents are used in Snapshot Replication, snapshot and distribution. Snapshot Agent:  A shared agent for all replication types.  The snapshot agent’s job is to generate data scripts for the objects you are replicating.  These scripts are written to a folder in the file system called a snapshot folder. Distribution Agent:  This agent will read from a snapshot folder and distribution database to propagate to the subscriber end.
Replication Types Transactional: The most used replication type The most valuable feature of the transactional replication is the ability to replicate incremental changes rather than applying the alldata set. Use transactional log to generate transactions for replication. Here are the scenarios where you can use transactional replication:  Replicate huge volumes of data  For realtime application  Replicate data between nonSQL Server databases
Replication Types Transactional: The most used replication type The most valuable feature of the transactional replication is the ability to replicate incremental changes rather than applying the alldata set. Use transactional log to generate transactions for replication. Here are the scenarios where you can use transactional replication:  Replicate huge volumes of data  For realtime application  Replicate data between nonSQL Server databases
Replication Types PeertoPeer Replication Peertopeer replication is an option with transactional replication All nodes in a peertopeer replication topology subscribe and publish from and to all other nodes. A transaction originating at one node will be replicated to all other nodes, but not replicated back to originator. This replication model is intended for use in applications to have multiple databases or database servers participating in a scaleout solution.
Replication Types Merge Replication Start from the initial snapshot. Afterward, changes at both publisher and subscriber(s) are tracked with triggers. Subsequent data changes and schema modifications made at the Publisher and Subscribers are tracked with triggers. The Subscriber synchronizes with the Publisher when connected to the network and exchanges all rows that have changed between the Publisher and Subscriber since the last time synchronization occurred.

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