On 23/06/2020 14:42, Klaudie Willis wrote:
I got my first hint of why this problem occurs when I looked at the statistics. For the column in question, "instrument_ref" the statistics claimed it to be:
The default_statistics_target=500, and analyze has been run.
select * from pg_stats where attname like 'instr%_ref'; -- Result: 40.000
select count(distinct instrumentid_ref) from bigtable -- Result: 33 385 922 (!!)
That is an astonishing difference of almost a 1000X.
I think you are counting 2 different things here.
The first query returns all the columns "like 'instr%_ref'" present in the statistics (so in the whole cluster), while the second is counting the actual number of different rows in bigtable.
regards,
fabio pardi