Re: Logging checkpoints and other slowdown causes

On Tue, 29 May 2007, Heikki Linnakangas wrote:

> The checkpoint will take at least a couple of seconds on any interesting
> system, so 0.1 s resolution should be enough IMHO.

You may be underestimating the resources some interesting systems are
willing to put into speeding up checkpoints.  I'm sometimes dumping into a
SAN whose cache is bigger than the shared_buffer cache in the server, and
0.1s isn't really enough resolution in that situation.  A second is a
really long checkpoint there.  Since even that's limited by fiber-channel
speeds, I know it's possible to do better than what I'm seeing with
something like a PCIe host adapter having on-board cache in the GB range
(which isn't that expensive nowadays).

Also, even if the checkpoint total takes seconds, much of that is in the
sync phase; the write time can still be in the small number of ms range,
and I wouldn't want to see that truncated too much.

Anyway, I have a bunch of data on this subject being collected at this
moment, and I'll rescale the results based on what I see after analyzing
that this week.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD