From: | "Zeugswetter Andreas ADI SD" <ZeugswetterA(at)spardat(dot)at> |
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To: | "Simon Riggs" <simon(at)2ndquadrant(dot)com>, "ITAGAKI Takahiro" <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp> |
Cc: | "PostgreSQL-development" <pgsql-hackers(at)postgresql(dot)org>, "Greg Smith" <gsmith(at)gregsmith(dot)com>, "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> |
Subject: | Re: Sorted writes in checkpoint |
Date: | 2007-06-15 09:14:20 |
Message-ID: | E1539E0ED7043848906A8FF995BDA579022414E0@m0143.s-mxs.net |
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Lists: | pgsql-hackers pgsql-patches |
> > tests | pgbench | DBT-2 response time
> (avg/90%/max)
> >
> ---------------------------+---------+--------------------------------
> > ---------------------------+---------+---
> > LDC only | 181 tps | 1.12 / 4.38 / 12.13 s
> > + BM_CHECKPOINT_NEEDED(*) | 187 tps | 0.83 / 2.68 / 9.26 s
> > + Sorted writes | 224 tps | 0.36 / 0.80 / 8.11 s
> >
> > (*) Don't write buffers that were dirtied after starting
> the checkpoint.
> >
> > machine : 2GB-ram, SCSI*4 RAID-5
> > pgbench : -s400 -t40000 -c10 (about 5GB of database)
> > DBT-2 : 60WH (about 6GB of database)
>
> I'm very surprised by the BM_CHECKPOINT_NEEDED results. What
> percentage of writes has been saved by doing that? We would
> expect a small percentage of blocks only and so that
> shouldn't make a significant difference. I thought we
Wouldn't pages that are dirtied during the checkpoint also usually be
rather hot ?
Thus if we lock one of those for writing, the chances are high that a
client needs to wait for the lock ?
A write os call should usually be very fast, but when the IO gets
bottlenecked it might easily become slower.
Probably the recent result, that it saves ~53% of the writes, is
sufficient explanation though.
Very nice results :-) Looks like we want all of it including the sort.
Andreas
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