SQL Replication Terminologies.
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The following is a list of the terminology used with SQL Server Replication.
Replication : The capability to copy (i.e. replicate) data and changes to that data from one database to another.
Snapshot Agent : The Replication Snapshot Agent is an executable file that prepares snapshot files containing schema and data of published tables and database objects, stores the files in the snapshot folder, and records synchronization jobs in the distribution database.
Article : An article can be an entire table, select rows from a table, specified columns from a table or a stored procedures, Used defined functions, Views. An article is what is to be replicated.
Distribution Agent : The distribution agent is a process that moves transactions and snapshots held in the distribution database to subscribers.
Distribution Database :
- A distribution database tracks the changes (to publications) that need to be replicated (from publishers). A publisher can act as its own distributor, or a remote database server can be used to hold the distribution database.
- For transactional replication, the distribution database tracks changes made to publications.
- For merge replication it stores only synchronization history.
Distributor : The server that contains the distribution database.
Merge Agent : The merge agent is a process that merges changes between publication and subscription databases where merge replication is used.
Merge Replication : Type of replication that allows changes to the data to be made at any site. Changes to publications are then merged with the copies of that publication held at the other server(s). Merge replication cannot guarantee transactional consistency because the same or related records can be updated on different servers at the same time.
Publication : The data to be replicated is contained with a publication. A publication can contain a selection of tables and stored procedures. A table included in a publication is called an article. A publication therefore defines the set of data that is to be replicated. Each publication can be replicated as a snapshot publication (using snapshot replication), a transactional publication (using transactional replication) or a merge publication (using merge replication).
Publisher : A publisher is a server that makes data available for other servers, i.e. it is the server that makes data available for replication.
Pull Subscription : With pull subscription the subscriber asks the publisher for periodic updates. With pull subscription each subscriber can specify the best time for the update. Pull subscription is generally considered the better form of replication when a large number of subscribers are involved, or where the load on the LAN needs to be distributed.
Push Subscription : With push subscription the publisher pushes any changes made to the data out to the subscribers. Typically push subscription is used where changes need to be replicated to the subscribers shortly after the change occurs, i.e. where the the replication of changes is required in near real time.
Snapshot replication : Type of replication where a snapshot is taken of the current publication data. The subscriber's copy of the data is then replaced with the entire contents of that snapshot. Snapshot replication requires less processor overhead than either merge or transaction replication because it does not require continuous monitoring of data changes. Probably not suitable for replicating large volumes of data (i.e. large tables) because of the network traffic involved.
Subscriber : A subscriber is a server that receives updates to the data. Each subscriber is associated with a publisher.
Transactional Replication : Type of replication where the copies of the transactions are replicated to each subscriber. Transactional replication uses the transaction log to capture changes. These changes are then sent to subscribers and applied in the same order. This guarantees transactional consistency. Transactional replication is well suited where near real-time updates are required.
Replication : The capability to copy (i.e. replicate) data and changes to that data from one database to another.
Snapshot Agent : The Replication Snapshot Agent is an executable file that prepares snapshot files containing schema and data of published tables and database objects, stores the files in the snapshot folder, and records synchronization jobs in the distribution database.
Article : An article can be an entire table, select rows from a table, specified columns from a table or a stored procedures, Used defined functions, Views. An article is what is to be replicated.
Distribution Agent : The distribution agent is a process that moves transactions and snapshots held in the distribution database to subscribers.
Distribution Database :
- A distribution database tracks the changes (to publications) that need to be replicated (from publishers). A publisher can act as its own distributor, or a remote database server can be used to hold the distribution database.
- For transactional replication, the distribution database tracks changes made to publications.
- For merge replication it stores only synchronization history.
Distributor : The server that contains the distribution database.
Merge Agent : The merge agent is a process that merges changes between publication and subscription databases where merge replication is used.
Merge Replication : Type of replication that allows changes to the data to be made at any site. Changes to publications are then merged with the copies of that publication held at the other server(s). Merge replication cannot guarantee transactional consistency because the same or related records can be updated on different servers at the same time.
Publication : The data to be replicated is contained with a publication. A publication can contain a selection of tables and stored procedures. A table included in a publication is called an article. A publication therefore defines the set of data that is to be replicated. Each publication can be replicated as a snapshot publication (using snapshot replication), a transactional publication (using transactional replication) or a merge publication (using merge replication).
Publisher : A publisher is a server that makes data available for other servers, i.e. it is the server that makes data available for replication.
Pull Subscription : With pull subscription the subscriber asks the publisher for periodic updates. With pull subscription each subscriber can specify the best time for the update. Pull subscription is generally considered the better form of replication when a large number of subscribers are involved, or where the load on the LAN needs to be distributed.
Push Subscription : With push subscription the publisher pushes any changes made to the data out to the subscribers. Typically push subscription is used where changes need to be replicated to the subscribers shortly after the change occurs, i.e. where the the replication of changes is required in near real time.
Snapshot replication : Type of replication where a snapshot is taken of the current publication data. The subscriber's copy of the data is then replaced with the entire contents of that snapshot. Snapshot replication requires less processor overhead than either merge or transaction replication because it does not require continuous monitoring of data changes. Probably not suitable for replicating large volumes of data (i.e. large tables) because of the network traffic involved.
Subscriber : A subscriber is a server that receives updates to the data. Each subscriber is associated with a publisher.
Transactional Replication : Type of replication where the copies of the transactions are replicated to each subscriber. Transactional replication uses the transaction log to capture changes. These changes are then sent to subscribers and applied in the same order. This guarantees transactional consistency. Transactional replication is well suited where near real-time updates are required.
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