I had to let this go and get on with testing DB2 on Solaris. I had to
abandon zfs on local discs in x64 Solaris 10 5/08.
The situation was that:
* DB2 buffer pools occupied up to 90% of 32GB RAM on each host
* DB2 cached the entire database in its buffer pools
o having the file system repeat this was not helpful
* running high-load DB2 tests for 2 weeks showed 100% file-system
writes and practically no reads
Having database tables on zfs meant launching applications took minutes
instead of sub-second.
The test configuration I ended up with was:
* transaction logs worked well to zfs on SAN with compression
(nearly 1 TB of logs)
* database tables worked well with ufs directio to multiple SCSI
discs on each of 4 hosts (using DB2 database partitioning feature)
I refer to DIRECTIO only as this already provides a reasonable set of
hints to the OS:
* reads and writes need not be cached
* write() should not return until data is in non-volatile storage
o DB2 has multiple concurrent write() threads to optimize this
strategy
* I/O will usually be in whole blocks aligned on block boundaries
As an aside: It should be possible to state to zfs that a device cache
is non-volatile (e.g. on SAN) and does not need flushing. Otherwise SAN
must be configured to ignore all cache flush commands.
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