I've been studying the output of the MON$IO_STATS table but something doesn't
make sense. I've built a test rig that
a) catches the mon$io_stats to disk at the attachment level on disconnect
and
b) modifies a million records randomly during a single attachment.
After this update completes gstat is telling me that the database has
increased by approximately X pages. However the page i/o statistics are
telling me that the attachment only wrote Y pages.
Here are some more detailed figures:
Page Size GSTAT Before GSTAT After GSTAT Diff MON$IO Page Writes
========= ============ =========== ========== ==================
4096 250000 315049 115049 1561
8192 111112 140824 29712 7602
16384 55556 70214 14658 22320
I've repeated the tests several times with similar results.
I'm also noticing that the cumulative figure for stat_group 0 in MON$IO_STATS
does not even match the figures I'm getting from my capture of stats at the
attachment level.
So, the question is - just what page writes are counted? I have been convinced
for at least the last fifteen years that the stats counted all physical page
i/o. This does not seem to be the case.
(Tests carried out with 2.1.4 SS on Linux, btw.)
Paul
--
Paul Reeves
http://www.ibphoenix.com
Specialists in Firebird support
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