Commit Scopes v5.6
EDB Postgres Distributed (PGD) offers a range of synchronous modes to complement its default asynchronous replication. You use commit scopes to configure these synchronous modes. Commit scopes are rules that define how PGD handles synchronous operations and when the system considers a transaction committed.
Introducing
Overview introduces the concepts and some of the essential terminology that's used when discussing synchronous commits.
Durability terminology lists terms used around PGD's durability options, including how to refer to nodes in replication.
Commit scopes is a more in-depth look at the structure of commit scopes and how to define them for your needs.
Commit scope rules looks at the syntax of and how to compose a commit scope rule.
Comparing durability options compares how commit scope options behave with regard to durability.
Degrading commit scope rules shows how to set up a commit scope rule that can gracefully degrade to a lower setting in case of timeouts with a stricter setting.
Commit scope kinds
Synchronous Commit is a commit scope mechanism that works in a similar fashion to legacy synchronous replication, but from within the commit scope framework.
Group Commit focuses on the Group Commit option, where you can define a transaction as done when a group of nodes agrees it's done.
CAMO focuses on the Commit At Most Once option, in which applications take responsibility for verifying that a transaction has been committed before retrying. This ensures that their commits only happen at most once.
Lag Control looks at the commit scope mechanism which dynamically throttle nodes according to the slowest node and regulates how far out of sync nodes may go when a database node goes out of service.
Working with commit scopes
Administering addresses how to manage a PGD cluster with Group Commit in use.
Limitations lists the various combinations of durability options that aren't currently supported or aren't possible. Refer to this before deciding on a durability strategy.
Legacy synchronous replication shows how you can still access traditional Postgres synchronous operations under PGD.
Internal timing of operations compares legacy replication with PGD's async and synchronous operations, especially the difference in the order by which transactions are flushed to disk or made visible.