Subject: streaming replication confusion

From: Josh Kupershmidt <[email-masked]>
Date: Thu, 8 Nov 2012 19:56:00 -0700

I think there is at least[4] one confusing documentation leftover from
the 9.0 days at:
  http://www.postgresql.org/docs/devel/static/warm-standby.html

First, we claim:

| Streaming replication is asynchronous, so there is still a small delay
| between committing a transaction in the primary and for the changes
| to become visible in the standby.

This unqualified statement, which has remained the same since 9.0,
suggests synchronous replication is not possible using streaming
replication. Further down we are closer to the truth:

| PostgreSQL streaming replication is asynchronous by default.

Proposed fix for this gripe attached. I'd be pleased to see this
particular doc patch backpatched to 9.2 and 9.1, given that the
replication docs are both important and fairly confusing.

The Streaming Replication wiki page[1] contains similar out-of-date
claims[2]; I can fix some of the egregious errors myself, though help
is welcome. The "Synchronous Replication" wiki page[3] is in even
worse shape, containing mostly info about a patch different than what
was committed... and it's currently the first Google search result for
"postgresql synchronous replication" :-(

Josh

[1] http://wiki.postgresql.org/wiki/Streaming_Replication
[2] such as "Currently SR supports only asynchronous log-shipping", or
already-released functionality described under the "Future release
section".
[3] http://wiki.postgresql.org/wiki/Synchronous_replication
[4] I have a larger gripe about the way this entire page is laid out,
with streaming rep. info bolted onto a page which is still named and
was intended to be about warm standby, but I'll try to make a separate
thread about that.

---

From: Josh Kupershmidt <[email-masked]>
Date: Sat, 5 Jan 2013 11:26:38 -0700

> "postgresql synchronous replication" :-(

I've shuffled around the Synchronous replication page, and made some
changes to Streaming Replication, though the latter could probably use
some further pruning. Could someone take a look at the small
documentation patch?

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From: Magnus Hagander <[email-masked]>
Date: Thu, 17 Jan 2013 14:54:29 +0100

> some further pruning. Could someone take a look at the small

Was that message supposed to contain a second patch, or were you just
referring to the one you sent back in November?

--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/

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From: Josh Kupershmidt <[email-masked]>
Date: Thu, 17 Jan 2013 08:04:41 -0700

> referring to the one you sent back in November?

I was referring to the initial patch sent in November.

Josh

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From: Magnus Hagander <[email-masked]>
Date: Sun, 20 Jan 2013 16:13:32 +0100

> I was referring to the initial patch sent in November.

Ok, thanks for confirming. Applied and backpatched.