From: Jesper Pedersen <jesper.pedersen@redhat.com>
To: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: Jeevan Ladhe <jeevan.ladhe@enterprisedb.com>
Cc: Pg Hackers <pgsql-hackers@postgresql.org>
Subject: Re: partition tree inspection functions
Date: Fri, 20 Jul 2018 08:26:03 -0400
Message-ID: <da9f8b6d-13bb-18fe-7777-b3be7bdd327b@redhat.com> (raw)
In-Reply-To: <5686970f-b4e8-bbe5-9109-b97763714c19@lab.ntt.co.jp>
References: <8d00e51a-9a51-ad02-d53e-ba6bf50b2e52@lab.ntt.co.jp>
<5a560c9c-3722-1914-f34b-1de0ff3310d1@lab.ntt.co.jp>
<CAOgcT0P8FC4Sat1ytVZgm09qd2bgMv-7pWpvU1HdBMKSah9r-w@mail.gmail.com>
<d5f5b9a8-0c88-8043-2007-be37096bed39@lab.ntt.co.jp>
<20180627121615.GF2667@paquier.xyz>
<45e28062-976d-45bf-56f8-9746f551da02@lab.ntt.co.jp>
<20180628034341.GH11054@paquier.xyz>
<6baeb45a-6222-6b88-342d-37fc7d3cf89a@lab.ntt.co.jp>
<4f4a2518-6c62-5463-6ac2-1241ae9d6041@redhat.com>
<e12ff710-dcf5-18ff-b4a4-cc42432d84c4@lab.ntt.co.jp>
<38183355-ea7c-9443-0c38-6124fcf5f38b@redhat.com>
<5686970f-b4e8-bbe5-9109-b97763714c19@lab.ntt.co.jp>
Hi Amit,
On 07/19/2018 10:27 PM, Amit Langote wrote:
> On 2018/07/19 23:18, Jesper Pedersen wrote:
>> I'm thinking about how to best use these functions to generate a graph
>> that represents the partition hierarchy.
>>
>> What about renaming pg_partition_tree_tables() to pg_partition_children(),
>> and have it work like
>>
>> select * from pg_partition_children('p', true);
>> ---------
>> p
>> p0
>> p1
>> p00
>> p01
>> p10
>> p11
>> (7 rows)
>>
>> select * from pg_partition_children('p', false);
>> ---------
>> p0
>> p1
>> (2 rows)
>>
>> e.g. if 'bool include_all' is true all nodes under the node, including
>> itself, are fetched. With false only nodes directly under the node,
>> excluding itself, are returned. If there are no children NULL is returned.
>
> That's a big change to make to what this function does, but if that's
> what's useful we could make it. As an alternative, wouldn't it help to
> implement the idea that Dilip mentioned upthread of providing a function
> to report the level of a given table in the partition hierarchy -- 0 for
> root, 1 for its partitions and so on?
>
Yes, Dilip's idea could work. I just don't think that
pg_partition_tree_tables() as is would have a benefit over time.
> Basically, as also discussed before, users can already use SQL to get the
> information they want out of the relevant catalogs (pg_inherits, etc.).
> But, such user queries might not be very future-proof as we might want to
> change the catalog organization in the future, so we'd like to provide
> users a proper interface to begin with. Keeping that in mind, it'd be
> better to think carefully about what we ought to be doing here. Input
> like yours is greatly helpful for that.
>
We could have the patch include pg_partition_root_parent and
pg_partition_parent, and leave the rest for a future CommitFest such
that more people could provide feedback on what they would like to see
in this space.
>>>> Maybe a function like pg_partition_number_of_partitions() could be of
>>>> benefit to count the number of actual partitions in a tree. Especially
>>>> useful in complex scenarios,
>>>>
>>>> select pg_partition_number_of_partitions('p') as number;
>>>>
>>>> number
>>>> ---------
>>>> 4
>>>> (1 row)
>>>
>>> Okay, adding one more function at this point may not be asking for too
>>> much. Although, select count(*) from pg_partition_tree_tables('p') would
>>> give you the count, a special function seems nice.
>>
>> Yeah, but I was thinking that the function would only return the number of
>> actual tables that contains data, e.g. not include 'p', 'p0' and 'p1' in
>> the count; otherwise you could use 'select count(*) from
>> pg_partition_children('p', true)' like you said.
>
> Maybe call it pg_partition_tree_leaf_count() or some such then?
>
That could work.
Best regards,
Jesper
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: jesper.pedersen@redhat.com, Langote_Amit_f8@lab.ntt.co.jp, michael@paquier.xyz, jeevan.ladhe@enterprisedb.com
Subject: Re: partition tree inspection functions
In-Reply-To: <da9f8b6d-13bb-18fe-7777-b3be7bdd327b@redhat.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox