Parallel query performance worse than without it

From: Andy <enzoweb_at_hotmail.com>
Date: 2 May 2002 15:24:23 -0700
Message-ID: <8d4033cd.0205021424.61cdbccb@posting.google.com>

Oracle V806.

I am doing some testing with parallel query:

optimizer_mode=rule, parallel_max_servers = 8, parallel_min_servers = 4 in the init.ora file.
The server has 4 cpus.

These are the results:

select * from cptrancopy;
281079 rows selected

	            No Parallel	Parallel=4
No statistics	    02:10.3	02:38.3
Statistics=10%	    01:57.0	02:14.8
Statistics=50%	    01:55.2	02:22.7
Compute statistics  02:35.1	02:39.2

Explain plan extract for parallel queries:

Execution Plan

   0      SELECT STATEMENT Optimizer=RULE (Cost=1679 Card=281079 Bytes
          =78702120)

1 0 TABLE ACCESS* (FULL) OF 'CPTRANCOPY' (Cost=1679 Card=28107 :Q28000

9 Bytes=78702120)

1 PARALLEL_TO_SERIAL SELECT /*+ ROWID(A1) */ A1."PTRAN_KEY",A1."P TR",A1."POSTFL",A1."CLNO",A1."ACT",A The Oracle manual states "Parallel execution is useful for operations that access a large amount of data by way of large table scans."

So, why the worse performance? It's a straightforward test, I expected it to work.

Thanks Received on Thu May 02 2002 - 17:24:23 CDT