Blog | Bugs | Build Farm | Events | Feature Requests | IRC | LCOV | Mailing List | Planet Drizzle | Source Code | Source Docs | Wiki
This page serves to document ongoing design and development of the Drizzle pluggable replication system
Contents |
Goals of the Replication System
There are only two major goals of the replication system as a whole. They are:
- Flexibility -- Allow environment-specific and targeted replication implementations to be written as pluggable modules
- Simplicity -- Replication API between the kernel and modules (and between modules themselves) shall be as simple as possible
Some may ask, "Well, shouldn't performance be a goal?" or "What about synchronous replication!?". No, neither of these are central to the goals of the replication system as a whole, though performance or synchronous replication may certainly be laudable goals of a specific module's implementation of replication internals. By focusing on making plugin/module developers lives easier (via simplicity of the API), we can further the targeted implementation goals of those modules.
Use Cases of Replication
Look here for discussion of Replication Use Cases.
Command GPB messages
At the core of the replication system API is the Command message. This is a Google Protobuffer Message class and is exchanged between the kernel and replication modules. The Command message describes an event which occurred inside the kernel in regards to a changing of storage data or data definitions (DML and DDL statements).
The Command message is passed to the various Replicator, Applier, and Reader Plugin APIs and is the "currency" exchanged between Publisher and Subscriber modules.
Command message proto
As always, to see the most up-to-date version of the Command message format, see the definition in /drizzled/message/transaction.proto. Over time, the format of the message may change slightly by adding optional members to the message.
The TransactionContext sub-message
Each Command message is guaranteed to have a TransactionContext submessage which defines some valuable information about the command itself.