Date: Wed, 19 Jan 2022 10:27:33 +0000
From: Victor Sudakov <vas@sibptus.ru>
To: pgsql-admin@lists.postgresql.org
Cc: Ron <ronljohnsonjr@gmail.com>
Subject: Re: Large number of partitions of a table
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Ron wrote:

[dd]

> >
> > What about the system catalogs however? Will the extra 10000
> > tables and 500000 indexes negatively impact the performance of the
> > system catalogs? Are there any caveats you could think of?
> 
> EXPLAIN plans are going to be hilariously gigantic, which means that query 
> planning would take a loooong time,  

No, I'm not observing this for my test queries. With
enable_partition_pruning=on (which is the default) all the queries
I've tested look neat and short.

> And the query planner (in v12, at 
> least) can generate some pretty bad plans in partitioned tables; I bet there 
> are edge cases in the QP code that don't work well with 10000 partitions and 
> 50000 indices.

Actually "5.11.6. Best Practices for Declarative Partitioning" says
"The query planner is generally able to handle partition hierarchies
with up to a few thousand partitions fairly well, provided that
typical queries allow the query planner to prune all but a small
number of partitions."

I admit 10000 partitions is slightly more than "a few thousand". "A
few" sounds to me like 3-5.

-- 
Victor Sudakov VAS4-RIPE
http://vas.tomsk.ru/
2:5005/49@fidonet