On 4/3/25 02:46, James Pang wrote:
Andrei,
   Yes, from explain output, since optimizer already get the merge_append cost but not take account into total cost, that make a big difference.  I shared table DDLs and explain analyze,buffers output , I think  the data maybe generated by other way to reproduce this issue. sorry for not sharing the commercial production data here.
I think it is almost enough to identify the issue. Let me ask you the following questions:
1. Can you provide min and max values in columns cc.sss_id and aa.mmm_id?
2. How often do you analyze your *parent* tables tablea and tablec? Remember, if you want to build statistics on a partitioned table (not a partition), you have to explicitly call

ANALYZE tablea,tablec;

mentioning these tables in the analyze list.

3. May you provide a dump of pg_statistic on attributes cc.sss_id and aa.mmm_id? 4. Is there a possibility of changing a single code line and rebuilding your DB instance to check a conjecture?

--
regards, Andrei Lepikhov


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