Date: Thu, 3 Jan 2019 09:39:00 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
Cc: "Imai, Yoshikazu" <imai.yoshikazu@jp.fujitsu.com>,
	David Rowley <david.rowley@2ndquadrant.com>,
	Alvaro Herrera <alvherre@2ndquadrant.com>,
	pgsql-hackers@postgresql.org
Subject: Re: speeding up planning with partitions
Message-ID: <20190103153900.GA6236@telsasoft.com>
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 <0F97FA9ABBDBE54F91744A9B37151A5122E7B1@g01jpexmbkw24>
 <08a6775f-7c88-81a8-8c2c-984d171b6db9@lab.ntt.co.jp>
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Hi,

I don't think I can't help with code review, but I loaded our largest
customer's schema into pg12dev and tested with this patch.  It's working well -
thanks for your work.

Details follow.

We have tooo many tables+indices so this vastly improves planning speed.  Our
large customers have ~300 parent tables and total ~20k child tables with total
~80k indices.  Our largest tables heirarchies have ~1200 child tables, which
may have as many as 6-8 indices each.  And 5-10 of the largest heirarchies are
unioned together in a view.

Running pg11.1, explaining query for the largest view with condition eliminates
all but today's tables can take several minutes with a cold cache, due to not
only stat()ing every file in every table in a partition heirarchy, before
pruning, but also actually open()ing all their indices.

Running 11dev with your v10 patch applied, this takes 2244ms with empty buffer
cache after postmaster restarted on a totally untuned instance (and a new
backend, with no cached opened files).

I was curious why it took even 2sec, and why it did so many opens() (but not
20k of them that PG11 does):

[pryzbyj@database postgresql]$ cut -d'(' -f1 /tmp/strace-12dev-explain |sort |uniq -c |sort -nr
   2544 lseek
   1263 open
   ...

It turns out 1050 open()s are due to historic data which is no longer being
loaded and therefor never converted to relkind=p (but hasn't exceeded the
retention interval so not yet DROPped, either).

Cheers,
Justin