Re: Timeline following for logical slots

Craig Ringer wrote:

> With this patch pg_recvlogical takes a new --endpos LSN argument, and will
> exit if either:
>
> * it receives an XLogData message with dataStart >= endpos; or
> * it receives a keepalive with walEnd >= endpos
>
> The latter allows it to work without needing a dummy transaction to make it
> see a data message after endpos. If there's nothing to read on the socket
> until a keepalive we know that the server has nothing to send us, and if
> walend has passed endpos we know nothing can have committed before endpos.

Here's a slightly revised version of this patch, for later
consideration.

Changes:
- added -E as short form of --endpos (consistent with -I as --startpos)
- refactored some repetitive code in two auxilliary functions
- allow --endpos to work with --create-slot.
- revert some unrelated changes, such as message additions in verbose
mode and changes to existing messages
- documentation reworked.

I didn't spot any bugs in Craig's patch, but it needs more testing.

--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services