On 2023-07-26 15:46:16 +0800, gzh wrote:
> SET enable_seqscan TO off;
[...]
> -> Parallel Bitmap Heap Scan on tbl_sha (cost=92112.45..2663789.14 rows=800650 width=18)
(actualtime=260.540..21442.169 rows=804500 loops=3)
> Recheck Cond: (ms_cd = 'MLD009'::bpchar)
> Rows Removed by Index Recheck: 49
> Filter: (etrys = '00000001'::bpchar)
> Rows Removed by Filter: 295500
> Heap Blocks: exact=13788 lossy=10565
> -> Bitmap Index Scan on index_search_04_mscd_cdate (cost=0.00..91632.06 rows=3402599
width=0)(actual time=249.718..249.718 rows=3300000 loops=1)
> Index Cond: (ms_cd = 'MLD009'::bpchar)
So now it's using index_search_04_mscd_cdate which contains only ms_cd
(and - judging from the name, other fields not relevant to this query),
but it still doesn't use index_search_01 which would fit the query
exactly. I can understand that Postgres prefers a sequential scan over
an index scan (the number of matching rows is about 10% of the total
table size which is a lot), but why would it prefer a less specific
index to a more specific one?
Can you get Postgres to use that index at all?
Find a combination of ms_cd and etrys which doesn't cover millions of
rows and try that.
Also try lowering random_page_cost.
hp
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_ | Peter J. Holzer | Story must make more sense than reality.
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| | | hjp@hjp.at | -- Charles Stross, "Creative writing
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