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Revert ill-considered change of index-size fudge factor.

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This partially reverts commit 21a39de5809cd3050a37d2554323cc1d0cbeed9d,
restoring the pre-9.2 cost estimates for index usage.  That change
introduced much too large a bias against larger indexes, as per reports
from Jeff Janes and others.  The whole thing needs a rewrite, which I've
done in HEAD, but the safest thing to do in 9.2 is just to undo this
multiplier change.
This commit is contained in:
Tom Lane 2013-01-11 13:08:19 -05:00
parent 0b3c54aac7
commit 3e9960e9d9
1 changed files with 2 additions and 2 deletions
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src/backend/utils/adt/selfuncs.c
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@ -6130,11 +6130,11 @@ genericcostestimate(PlannerInfo *root,
*
* We can deal with this by adding a very small "fudge factor" that
* depends on the index size. The fudge factor used here is one
* spc_random_page_cost per 10000 index pages, which should be small
* spc_random_page_cost per 100000 index pages, which should be small
* enough to not alter index-vs-seqscan decisions, but will prevent
* indexes of different sizes from looking exactly equally attractive.
*/
*indexTotalCost += index->pages * spc_random_page_cost / 10000.0;
*indexTotalCost += index->pages * spc_random_page_cost / 100000.0;
/*
* CPU cost: any complex expressions in the indexquals will need to be