On Thu, Apr 11, 2019 at 03:34:30PM +1200, David Rowley wrote:
> On Thu, 21 Mar 2019 at 00:51, David Rowley <david.row...@2ndquadrant.com>
> wrote:
> > Just so I don't forget about this, I've added it to the July 'fest.
> >
> > https://commitfest.postgresql.org/23/2065/
>
> Now that we have 428b260f8, I think the version of this that goes into
> master should be more like the attached.
I tweaked this patch some more (sorry):
- remove "currently" since that's not expected to be changed (right?);
- remove "especially";
- refer to "partition hierarchies" not "partitioning hierarchies";
- rewrite bit about "When partition pruning is not possible"
Also, I noticed awhile ago while grepping for "probably be fixed in future
releases" that some items under ddl-inherit-caveats are actually possible for
relkind=p partitions in v11. I assume those will never be implemented for
inheritence partitioning, so I propose another update to docs (if preferred,
I'll bring up on a new thread).
- unique constraints on parent table;
- FK constraints on parent table;
Note that FK constraints *referencing* a partitiond table are possible in v12
but not in v11. So if there's any finer-grained update to documentation of the
individual limitations, it'd need to be tweaked for back branches (v10 and 11).
Justin
>From 3a787b95f5a35b53cd958855ec6fc4ff9fc9a455 Mon Sep 17 00:00:00 2001
From: Justin Pryzby <pryz...@telsasoft.com>
Date: Thu, 11 Apr 2019 00:24:44 -0500
Subject: [PATCH v1 1/2] Reinstate warnings regarding large heirarchies
Put back warnings regarding high planning time and/or RAM use for large
inheritance heirarchies, and high planning time for large number of partitions
not pruned during planning with declaratively partitioned tables.
Discussion:
https://www.postgresql.org/message-id/CAKJS1f8RW-mHQ8aEWD5Dv0%2B8A1wH5tHHdYMGW9y5sXqnE0X9wA%40mail.gmail.com
https://commitfest.postgresql.org/23/2065/
Author: Robert Haas, David Rowley
Reviewed by: Amit Langote, Justin Pryzby
---
doc/src/sgml/ddl.sgml | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 244d5ce..83cbc66 100644
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -3582,6 +3582,26 @@ VALUES ('Albany', NULL, NULL, 'NY');
offer flexibility but do not have some of the performance benefits
of built-in declarative partitioning.
</para>
+
+ <note>
+ <para>
+ When using table inheritance, partition hierarchies with more than a few
+ hundred partitions are not recommended. Larger partition hierarchies may
+ incur long planning time, and, in the case of <command>UPDATE</command>
+ and <command>DELETE</command>, excessive memory usage. When inheritance
+ is used, see also the limitations described in
+ <xref linkend="ddl-partitioning-constraint-exclusion"/>.
+ </para>
+
+ <para>
+ When using declarative partitioning, the overhead of query planning
+ is directly related to the number of unpruned partitions. Planning is
+ generally fast with small numbers of unpruned partitions, even in
+ partition hierarchies containing many thousands of partitions. However,
+ long planning time will be incurred by large partition hierarchies if
+ partition pruning is not possible during the planning phase.
+ </para>
+ </note>
</sect2>
<sect2 id="ddl-partitioning-declarative">
--
2.1.4
>From 6bd80e7cdddc3c9552d44439b4b8e9843c1007e4 Mon Sep 17 00:00:00 2001
From: Justin Pryzby <pryz...@telsasoft.com>
Date: Thu, 11 Apr 2019 00:22:56 -0500
Subject: [PATCH v1 2/2] Document features of declarative partitioning..
..which will never be implemented for legacy inheritance.
---
doc/src/sgml/ddl.sgml | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 83cbc66..3495a66 100644
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -3450,8 +3450,9 @@ VALUES ('Albany', NULL, NULL, 'NY');
</listitem>
</itemizedlist>
- These deficiencies will probably be fixed in some future release,
- but in the meantime considerable care is needed in deciding whether
+ Some functionality not implemented for inheritance hierarchies is
+ implemented for declarative partitioning.
+ Considerable care is needed in deciding whether partitioning with legacy
inheritance is useful for your application.
</para>
--
2.1.4
