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Re: Controlling Load Distributed Checkpoints

From: Gregory Stark <stark(at)enterprisedb(dot)com>
To: "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>
Cc: "PostgreSQL-development" <pgsql-hackers(at)postgresql(dot)org>, "ITAGAKI Takahiro" <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, "Greg Smith" <gsmith(at)gregsmith(dot)com>
Subject: Re: Controlling Load Distributed Checkpoints
Date: 2007-06-06 14:14:14
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Lists: pgsql-hackerspgsql-patches
"Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> writes:

> GUC summary and suggested default values
> ----------------------------------------
> checkpoint_write_percent = 50 		# % of checkpoint interval to spread out writes
> checkpoint_write_min_rate = 1000	# minimum I/O rate to write dirty
> buffers at checkpoint (KB/s)

I don't understand why this is a min_rate rather than a max_rate.

> checkpoint_nap_duration = 2 		# delay between write and sync phase, in seconds

Not a comment on the choice of guc parameters, but don't we expect useful
values of this to be much closer to 30 than 0? I understand it might not be
exactly 30.

Actually, it's not so much whether there's any write traffic to the data files
during the nap that matters, it's whether there's more traffic during the nap
than during the 30s or so prior to the nap. As long as it's a steady-state
condition it shouldn't matter how long we wait, should it?

> checkpoint_fsync_period = 30		# duration of the sync phase, in seconds
> checkpoint_fsync_delay = 500		# max. delay between fsyncs

  Gregory Stark

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