On Sat, Nov 23, 2019 at 2:39 AM Nikita Glukhov <n.glu...@postgrespro.ru> wrote: > Attached 8th version of the patches.
I've read this thread. I decided to rewrite the patch in the way, which I find simple and more clear. Attached is the draft patch written from scratch except regression tests, which were copied "as is". It based on the discussion in this thread as well as my own ideas. It works as following. 1) New GinScanKey->excludeOnly flag is introduced. This flag means that scan key might be satisfied even if no of its entries match the row. So, such scan keys are useful only for additional check of results returned by other keys. That is excludeOnly scan key is designed for exclusion of already obtained results. 2) Initially no hidden scan entries are appended to GIN_SEARCH_MODE_ALL scan keys. They are appended after getting statistics about search modes applied to particular attributes. 3) We append at only one GIN_CAT_EMPTY_QUERY scan entry when all scan keys GIN_SEARCH_MODE_ALL. If there is at least one normal scan key, no GIN_CAT_EMPTY_QUERY is appended. 4) No hidden entries are appended to GIN_SEARCH_MODE_ALL scan key if there are normal scan keys for the same column. Otherwise GIN_CAT_NULL_KEY hidden entry is appended. 5) GIN_SEARCH_MODE_ALL scan keys, which don't have GIN_CAT_EMPTY_QUERY hidden entry, are marked with excludeOnly flag. So, they are used to filter results of other scan keys. 6) GIN_CAT_NULL_KEY hidden entry is found, then scan key doesn't match independently on result of consistent function call. Therefore, attached patch removes unnecessary GIN_CAT_EMPTY_QUERY scan entries without removing positive effect of filtering in GIN_SEARCH_MODE_ALL scan keys. Patch requires further polishing including comments, minor refactoring etc. I'm going to continue work on this. ------ Alexander Korotkov Postgres Professional: http://www.postgrespro.com The Russian Postgres Company
0001-Avoid-GIN-full-scan-for-empty-ALL-keys-v09.patch
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