When using parallel query, you have one master session, and several
parallel query slaves. Those query slaves need to be coordinated, and
there is messaging between the query slaves and the master.
The original session functions as master.
The general principle of parallel query is that it will use the divide
and conquer approach.
If you have a FTS, every parallel query slave will scan it's own part
of the table.
However,my tests (on I admit, 8i) have shown, that when all query
slaves are hitting one single disk, parallel query is prettty useless,
and will provide slower response time, *because of* the coordination
necessary.
Your situation may be similar, my crystal ball doesn't operate on the
insufficient detail you provide.
In short: using parallel query indiscriminately may be dangerous, and
parallel query is useless if you have only 2 CPUs (as one will be used
to coordinate the query slaves, so there will be contention for CPU).
--
Sybrand Bakker
Senior Oracle DBA
Received on Mon Jul 18 2005 - 03:07:30 CDT
