From: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-patches(at)postgresql(dot)org |
Subject: | Re: Miscalculation in IsCheckpointOnSchedule() |
Date: | 2007-11-14 11:47:08 |
Message-ID: | 473AE03C.9040406@enterprisedb.com |
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Lists: | pgsql-patches |
Tom Lane wrote:
> ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp> writes:
>> - ((double) (int32) (recptr.xrecoff - ckpt_start_recptr.xrecoff)) / XLogSegSize) /
>> + ((double) recptr.xrecoff - (double) ckpt_start_recptr.xrecoff) / XLogSegSize) /
>
> Surely this makes matters worse, not better. What happens near a segment
> boundary crossing?
Hmm. There seems to be another little bug in there. XLogSegsPerFile is
defined as 0xffffffff/XLogSegSize, which is 255 with default settings.
It should be 256. That leads to negative elapsed_xlogs estimates at xlog
file boundaries. XLogCheckpointNeeded suffers from it too; the number of
segments consumed since last checkpoint is off by one per each xlogid,
so we trigger the checkpoint a little bit too late.
Otherwise, the patch looks good to me. I also tested the calculation
with a little C program (attached), and it seems to work on segment and
xlog file boundaries just fine.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
Attachment | Content-Type | Size |
---|---|---|
xlog-arithmetic.c | text/x-csrc | 1.4 KB |
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