Re: Catalog views failed to show partitioned table information.

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
Cc: Suraj Kharage <suraj(dot)kharage(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Catalog views failed to show partitioned table information.
Date: 2018-12-17 02:01:59
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On Mon, Dec 17, 2018 at 10:22:28AM +0900, Amit Langote wrote:
> On 2018/12/15 8:00, Michael Paquier wrote:
>> I tend to agree with your comment here. pg_tables lists partitioned
>> tables, but pg_indexes is forgotting about partitioned indexes. So this
>> is a good thing to add.
> +1

I'll go commit something close to what Suraj is proposing if there are
no objections from others. At least we agree on that part ;)

>> I am less sure about that as partitioned relations do not have a
>> physical presence.
> Hmm, although most of the fields of pg_stat_user_tables would be NULL or 0
> for partitioned tables/indexes, values of at least some of the fields of
> pg_stat_user_tables, like last_vacuum, last_analyze, etc., might be useful
> to users. Also, we cannot assume that these views will continue to be
> mostly useless as far as partitioned relations are concerned.

Well, when VACUUM or ANALYZE list a partitioned table what the
processing does is to decompose partitioned tables into a list of actual
relations it can work on, and it never processes the partitioned parts,
so last_vacuum & friends remain set at 0/NULL.

We had a similar discussion about that a couple of months ago, and it
was not really clear to me how it is possible to define aggregates for
partitioned tables when analyzing them, and if stat tables should show
them or not:

Listing only NULL/0 is also confusing I think because this would mean
for the end-user that VACUUM and/or ANALYZE have never been run for a
given relation.

pg_partition_tree has been added since then, so compiling stats has
become easier for full partition trees, the documentation could be
improved on that point perhaps.

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