RE: Sudden plan change related to "VIEW PUSHED PREDICATE" with cost difference of 1M VS 13G
Date: Thu, 12 May 2022 20:14:42 +0000
Message-ID: <7a2deef0d7fa46478f4cf2aa24f77dd8_at_vontobel.com>
Hello Pap
I revisited my suggestion about column statistics - it was wrong. The low selectivity led to the JPPD transformation cost similar to the one that was in the plan with JPPD.
JPPD: Updated best state, Cost = 39.073380
If we multiply the cost above with the number of rows of the outer query block and add the cost of the outer join query block, we get the total cost of the plan with JPPD. It’s much lower than the plan without JPPD and similar to the cost of the good plan you’ve had previously:
20710 * 39.073380 + ~260K ~ 1M
So JPPD should definitely be selected.
The optimizer figured out that correctly and updated the best state with the cost of JPPD (39.07 is the cost of a single iteration):
JPPD: Updated best state, Cost = 39.073380
But then, it discarded it soon, for still unknown reason:
JPPD: Will not use JPPD from query block SEL$B29E968D
You mentioned that you edited out some lines from the optimizer trace. Are there any lines between the two lines mentioned above (“updated best state” and “Will not use JPPD” that might give the reason for not using JPPD? As already mentioned, the cost isn’t the reason.
If not, the following might be the reason:
A Optimizer applied some heuristics without logging it or
B The correct decision got overridden due to a bug
Could you try following:
Best regards,
Nenad
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Received on Thu May 12 2022 - 22:14:42 CEST