diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/utils/adt/selfuncs.c | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c index 61100aec4ae..60000aaf347 100644 --- a/src/backend/utils/adt/selfuncs.c +++ b/src/backend/utils/adt/selfuncs.c @@ -6130,12 +6130,14 @@ genericcostestimate(PlannerInfo *root, * index would have better selectivity.) * * 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 - * enough to not alter index-vs-seqscan decisions, but will prevent - * indexes of different sizes from looking exactly equally attractive. + * depends on the index size, so that indexes of different sizes won't + * look exactly equally attractive. To ensure the fudge factor stays + * small even for very large indexes, use a log function. (We previously + * used a factor of one spc_random_page_cost per 10000 index pages, which + * grew too large for large indexes. This expression has about the same + * growth rate for small indexes, but tails off quickly.) */ - *indexTotalCost += index->pages * spc_random_page_cost / 10000.0; + *indexTotalCost += log(1.0 + index->pages / 10000.0) * spc_random_page_cost; /* * CPU cost: any complex expressions in the indexquals will need to be |