Re: Miscalculation in IsCheckpointOnSchedule()

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