Steve writes:
>can someone a) tell me how to set these params and
>b) confirm that letting the system decide is a good idea?
>i am running UDB 7.1 fp5 on red hat 7.2.
Hello,
Many DBAs, myself included, thought that enabling intra-partition
parallelism would improve OLTP performance, but we quickly learned that
most units of work are too small in OLTP to benefit from parallelism. The
optimizer seems inclined to throw an extra subagent at even smallish
queries that would complete faster without the overhead introduced by
parallelism. This can be exacerbated by outdated or missing statistics. As
a result, you will find that most sources of trustworthy DB2 advice will
recommend leaving intra-partition parallelism turned off in OLTP.
However, decision support databases typically touch a lot more data per
statement (by scanning, sorting, prefetching, etc.) and are more likely to
make intelligent use of parallelism. Even then, you should leave the degree
set to -1 (automatic), since the optimizer doesn't usually pick a degree
that is higher than the number of installed CPUs.
Now that you have a second CPU, you can take advantage of parallelism in
any tablespaces with more than one container (or a container sitting on a
RAID array). I don't believe you even need to have intra-partition
parallelism turned on to use parallel I/O, but I may be wrong. If you
haven't enabled parallel I/O already, the DB2_PARALLEL_IO registry variable
will tell DB2 which tablespaces are eligible for parallelism. If you have
striped RAID arrays, you may also benefit from creating new tablespaces on
them after enabling DB2_STRIPED_CONTAINERS in the registry.
Hope this helps,
Fred Sobotka
CollegeNET
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