Planning of sub partitions

From: Matt Hughes <hughes(dot)matt(at)gmail(dot)com>
To: pgsql-general(at)lists(dot)postgresql(dot)org
Subject: Planning of sub partitions
Date: 2024-07-05 15:24:23
Message-ID: CANi6QLzHH1QySGK3r_WWu+FKxvCRXNBzvEY2dhFAA3XGuShg_g@mail.gmail.com
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-general

I am trying to model a stateful `event` table using partitions. An event
has date_raised (not null) and date_cleared (nullable) columns. An event
is in the "open" state when it has a null date_cleared; it is in the
"closed" state when date_cleared is set. Once date_cleared is set, it
won't change.

While most events close after a short period of time, a few stragglers stay
open for weeks or months. I'm trying to optimize my system for the
following things:

- I need to drop events older than N days; I want to use partitions so I
can just drop the table rather than an expensive DELETE
- Users want to see all open events OR closed events within the past N days

To do this, I came up with the following schema:

create table event (
id uuid not null,
cleared boolean not null,
date_raised timestamp without time zone not null,
date_cleared timestamp without time zone,
primary key (id, date_raised, cleared)
) PARTITION BY LIST (cleared);

CREATE TABLE event_open PARTITION OF event FOR VALUES IN (false);
CREATE TABLE event_closed PARTITION OF event FOR VALUES IN (true) partition
by range(date_raised);
CREATE TABLE event_closed_y2024_m01 PARTITION OF event_closed FOR VALUES
FROM ('2024-01-01') to ('2024-02-01');
CREATE TABLE event_closed_y2024_m02 PARTITION OF event_closed FOR VALUES
FROM ('2024-02-01') to ('2024-03-01');

This works for the most part but the plan for my compound query does not
behave as I would expect:

-- 1. correctly only picks event_open partition
explain select * from event where cleared is false;

-- 2. correctly picks all event_closed_* partitions
explain select * from event where cleared is true;

-- 3. correctly picks just the event_closed_y2024_m01 partition
explain select * from event where cleared is true and date_raised >
'2024-01-01' AND date_raised < '2024-01-02';

-- 4. uses all partitions; should exclude event_closed_y2024_m02
explain select * from event
where
cleared is false OR
(cleared is true and date_raised > '2024-01-01' AND date_raised <
'2024-01-02');

QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Append (cost=0.00..110.91 rows=2322 width=25)
-> Seq Scan on event_open event_1 (cost=0.00..33.10 rows=774 width=25)
Filter: ((cleared IS FALSE) OR ((date_raised > '2024-01-01
00:00:00'::timestamp without time zone) AND (date_raised < '2024-01-02
00:00:00'::timestamp without time zone)))
-> Seq Scan on event_closed_y2024_m01 event_2 (cost=0.00..33.10
rows=774 width=25)
Filter: ((cleared IS FALSE) OR ((date_raised > '2024-01-01
00:00:00'::timestamp without time zone) AND (date_raised < '2024-01-02
00:00:00'::timestamp without time zone)))
-> Seq Scan on event_closed_y2024_m02 event_3 (cost=0.00..33.10
rows=774 width=25)
Filter: ((cleared IS FALSE) OR ((date_raised > '2024-01-01
00:00:00'::timestamp without time zone) AND (date_raised < '2024-01-02
00:00:00'::timestamp without time zone)))

Is this a bug? Query 4 is just a union of queries 2/3 which pick the right
partitions. Do you see anything else wrong with this approach?

Note that `closed` column is somewhat of a hack as it is completely
computeable from `date_cleared is not null`. However, as I understand it,
partitions can only be declared on values that are part of the primary
key.

Responses

Browse pgsql-general by date

  From Date Subject
Next Message Peter J. Holzer 2024-07-05 15:40:35 Re: confused about material view locks please explain
Previous Message Adrian Klaver 2024-07-05 14:54:49 Re: Load a csv or a avro?