From: | "David F(dot) Skoll" <dfs(at)roaringpenguin(dot)com> |
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To: | pgsql-admin(at)postgresql(dot)org |
Subject: | Re: Weird spikes in delay for async streaming replication on 9.1 |
Date: | 2015-02-26 14:44:28 |
Message-ID: | 20150226094428.34531376@hydrogen.roaringpenguin.com |
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Thread: | |
Lists: | pgsql-admin |
Hi,
I posted this a couple of weeks ago and no response... I guess it's
quite mysterious.
Anyway, behavior is consistent. It seems that long-running
transactions on the primary (even read-only ones, because in my case
it's a pg_dump) can block subsequent transactions from appearing on
the hot-standby until the first transaction finishes. Is this a known
limitation? I run 9.1; is it still present in 9.4?
Regards,
David.
========================================================================
[...]
> I have a monitoring script that tests the actual delay for a
> transaction on the master to appear on the hot-standby. Every few
> minutes, my script runs an update on the master and then sits in a
> loop checking how long it takes to appear on the hot-standby. 99% of
> the time, it's less than a second.
> But every once in a while, the time spikes dramatically, to hundreds
> or thousands of seconds, and that's too long... the delay-tolerant
> queries are not *that* delay-tolerant, so we switch to sending them
> all to the master.
> See the graph: http://ibin.co/1rdm4ekiWmpM
[...]
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