Long checkpoint woe

IDS 10.0FC3 on Solaris 9. OLTP system.

Our system shows very long checkpoints (typically up to 10s, all day. Can
be up to a minute) for quite small amounts of dirty pages. We have
lru_min/max set so that the number of dirty ones never exceeds about 10,000.
As a checkpoint occurs we see through our monitor script the dirty page
count descend very slowly to 0 at a rate of about 1,000/s. (When I issued a
checkpoint during an ALTER FRAGMENT of a 4g table after I'd set lru_min/max
to 60 and 70, it took over half an hour!!).

I've had this open with IBM tech support for months. They've had me check
hardware, OS configuration etc etc, all of which have checked out fine, but
can't see a problem with Informix. Until the weekend we had one large 80g
dbspaces, but we took an outage at the weekend to split the busiest tables
in terms of writes out to separate dbspaces and now have a fairly even
balance over 5 dbspaces. It's made no difference at all

The IBM tech guy got me to create 2 20m slices then copy between them with a
2k page size. It does take a surprising amount of time with such a small
blocksize:

# time dd if=/dev/md/rdsk/d121 of=/dev/md/rdsk/d122 bs=2k
10240+0 records in
10240+0 records out

real 1m4.04s
user 0m0.03s
sys 0m0.64s

But id this really indicative of a problem?

Any other observations about the bigger Informix issue?

thanks
--
Neil Truby t:01932 724027
Director m:07798 811708
Ardenta Limited e:neil.truby@xxxxxxxxxxx


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