I would like to introduce concept of generic WAL logical messages.
Couple of points...
* Genenric misspelled
* You call them "logical messages" here, but standby messages in code. But they only apply to logical decoding, so "logical message" seems a better name. Can we avoid calling them "messages" cos that will get confusing.
For standard WAL reply, these are basically noop
We should document that.
These messages can be both transactional (decoded on commit) or non-transactional (decoded immediately). Each message has prefix to differentiate between individual plugins. The prefix has to be registered exactly once (in similar manner as security label providers) to avoid conflicts between plugins.
I'm not sure what "transactional" means, nor is that documented. (Conversely, I think "immediate" fairly clear)
Are they fired only on commit? (Guess so)
Are they fired in the original order, if multiple messages in same transaction? (Hope so)
Are they fired as they come in the original message sequence, or before anything else or after everything else? For example, cache invalidation messages are normally fired right at the end of a transaction, no matter when they were triggered.
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Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services