Lisa,
My experience with PQO has been that it can be very
beneficial even on single CPU machines, if used
judiciously and if, as you already mentioned, there
are sufficient resources. On the other hand it can
also bring a powerful server to its knees. "Tell me
again, why you thought setting parallel_max_server to
10000 and degree to 10 on all your tables was a good
idea?!" (true story, kid you not)
Keep in mind that PQO only benefits queries that are
doing full table scans and fast full scans (can't
remember if range scans can use it) and that PQO
forces the CBO to be used. The rows are divvied up
among the PQ slaves by rowid.
Note 39599.1 has a nice overview of PQO.
HTH,
- Anita
- "Koivu, Lisa" <lisa.koivu_at_efairfield.com> wrote:
> Hello everyone,
>
> I was reading up on the differences between SMP, MPP
> and how they may affect
> PQO (Parallel Query).
>
> My understanding is that MPP is a host with defined
> domains (like an e10k
> with virtual machines on it). SMP is a standalone
> host with no domains and
> multiple processors. I am not considering
> clustering here.
>
> It seemed to me the only requirement that you really
> need to run PQO is to
> have available resources to power it. For example,
> a little 2-cpu box that
> is pinned a majority of the time is only going to
> suffer if PQO is turned
> on. However, if we had a 16-cpu box with abundant
> resources, turning on PQO
> would help fts and large index scans in a dw-type
> environment. (At least
> this is what I saw in the past).
>
> Also, I was taught that PQO should not be used when
> a table/index is not
> partitioned. However, upon reading the doco, it
> states that the slaves
> split up work by blocks (or was it extents?). Seems
> to me this could cause
> more problems than it's worth (i/o contention?) and
> partitioning, if done
> carefully, would be the smarter way to go. Would
> the slaves really be smart
> enough to divy up work intelligently on a
> non-partitioned object? My
> initial thought is NO.
>
> In addition, on metalink they even went so far as to
> state it is OK to use
> PQO on a 2-processor NT machine. Seems to me the
> statement that 'PQO
> provides no benefit on a SMP machine' is not
> warranted, unless Oracle
> Support was just pacifying the customer who wanted
> to see PQO work.
>
> Maybe my idea of SMP is too simple. If I am off my
> rocker can someone
> please set me straight?
>
> Thanks
>
> > Lisa Koivu
> > Oracle Database Administrator
> > 954-935-4117
> >
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Received on Tue Jun 12 2001 - 12:51:18 CDT
