RE: Is important to GATHER_SYSTEM_STATS???
- From: ryan_gaffuri@xxxxxxxxxxx
- To: SMILEYJ@xxxxxxxx, "'jreyes@xxxxxxxxxxxxxxxx'" <jreyes@xxxxxxxxxxxxxxxx>, oracle-l@xxxxxxxxxxxxx
- Date: Fri, 22 Oct 2004 22:49:32 +0000
is anyone noticing an improving in the percentage of queries plans the CBO gets
right with this? With decent optimizer_index_cost_adj, optimizer_index_Caching,
and db_file_multiblock_read_Count, in verion 9.2 oracle appears to have a 99.5%
accuracy in plan generation even if you take into consideration the use of bind
variables and oracles inability to use histograms with them. .
not much to improve on if you use system stats.... We implemented it here and
we notice no improvement whatsoever.
> In a recent case, I was able to smooth the transition from nested loops to
> hash joins by setting system stats to appropriate values. Prior to this,
> the CBO would switch from NL to hash joins much too early, resulting in a
> big discontinuity in the response time curve for certain queries as the
> number of rows processed increased.
>
> Be sure to gather the stats during a load that represents the target state
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