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Re: Streaming Replication: Checkpoint_segment and wal_keep_segments on standby

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, "Sander, Ingo (NSN - DE/Munich)" <ingo(dot)sander(at)nsn(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Streaming Replication: Checkpoint_segment and wal_keep_segments on standby
Date: 2010-05-31 15:14:25
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Lists: pgsql-hackers
Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> The central question is whether checkpoint_segments should trigger 
> restartpoints or not. When PITR and restartpoints were introduced, the 
> answer was "no", on the grounds that when you're doing recovery you're 
> presumably replaying the logs much faster than they were generated, and 
> you don't want to slow down the recovery by checkpointing too often.

> Now that we have bgwriter active during recovery, and streaming 
> replication which retains the streamed WALs so that we now risk running 
> out of disk space with long checkpoint_timeout, it's time to reconsider 
> that.

> I think we have three options:

What about

(4) pay some attention to the actual elapsed time since the last
restart point?

All the others seem like kluges that are relying on hard-wired rules
that are hoped to achieve something like a time-based checkpoint.

			regards, tom lane

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