Re: Do table-level CHECK constraints affect the query optimizer?

On 6/29/21 10:41 AM, Michael Lewis wrote:
> Are vacuum and analyze happening regularly on the live system?

Yes.  There's a nightly cron job which vacuums those it thinks needs it
(though it's INSERT-heavy), and ditto ANALYZE.

Specifically, I ran ANALYZE on the prod table just before running the query.

Also, the sampling rate on all tables in both prod and test is 60000 rows.

> What's an example query that uses indexes on test and does not on live?

SELECT COUNT(*) FROM sep_info_report_extract;

On prod, there's a list of "Parallel Seq Scan on xxxx_partname" records in
the EXPLAIN output, while the test system has a list of "Parallel Index Only
Scan using ..._idx" records.

(Yes, this is a simple COUNT(*) but it's *a simple reproducer*, which
*demonstrates* the kind of problems we're having on *much more complex
queries*.)

> Does the live system show poor estimates when executing 'explain analyze
> select...' and the test system show semi-accurate row estimates?

They're within 2% of each other.

> 50 million seems to be a fairly low row count to be partitioned. What
> version is this on?

As explained in the OP, each record has a (sometimes large) XML record;
months can have up to 240GB.  Besides, partitioning makes for easy archiving.

--
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