Tag: partitions

Waiting for PostgreSQL 17 – MERGE / SPLIT partitions

I thought about it for quite some time, whether I should write about it, and how. That's why there is delay since:

On 6th of April 2024, Alexander Korotkov committed patch:

Implement ALTER TABLE ... MERGE PARTITIONS ... command
 
This new DDL command merges several partitions into the one partition of the
target table.  The target partition is created using new
createPartitionTable() function with parent partition as the template.
 
This commit comprises quite naive implementation which works in single process
and holds the ACCESS EXCLUSIVE LOCK on the parent table during all the
operations including the tuple routing.  This is why this new DDL command
can't be recommended for large partitioned tables under a high load.  However,
this implementation come in handy in certain cases even as is.
Also, it could be used as a foundation for future implementations with lesser
locking and possibly parallel.
 
Discussion: https://postgr.es/m/c73a1746-0cd0-6bdd-6b23-3ae0b7c0c582%40postgrespro.ru
Author: Dmitry Koval
Reviewed-by: Matthias van de Meent, Laurenz Albe, Zhihong Yu, Justin Pryzby
Reviewed-by: Alvaro Herrera, Robert Haas, Stephane Tachoires

and, also on 6th of April 2024, Alexander Korotkov committed patch:

Implement ALTER TABLE ... SPLIT PARTITION ... command
 
This new DDL command splits a single partition into several parititions.
Just like ALTER TABLE ... MERGE PARTITIONS ... command, new patitions are
created using createPartitionTable() function with parent partition as the
template.
 
This commit comprises quite naive implementation which works in single process
and holds the ACCESS EXCLUSIVE LOCK on the parent table during all the
operations including the tuple routing.  This is why this new DDL command
can't be recommended for large partitioned tables under a high load.  However,
this implementation come in handy in certain cases even as is.
Also, it could be used as a foundation for future implementations with lesser
locking and possibly parallel.
 
Discussion: https://postgr.es/m/c73a1746-0cd0-6bdd-6b23-3ae0b7c0c582%40postgrespro.ru
Author: Dmitry Koval
Reviewed-by: Matthias van de Meent, Laurenz Albe, Zhihong Yu, Justin Pryzby
Reviewed-by: Alvaro Herrera, Robert Haas, Stephane Tachoires

Continue reading Waiting for PostgreSQL 17 – MERGE / SPLIT partitions

Waiting for PostgreSQL 17 – Support identity columns in partitioned tables

On 16th of January 2024, Peter Eisentraut committed patch:

Support identity columns in partitioned tables
 
Previously, identity columns were disallowed on partitioned tables.
(The reason was mainly that no one had gotten around to working
through all the details to make it work.)  This makes it work now.
 
Some details on the behavior:
 
* A newly created partition inherits identity property
 
  The partitions of a partitioned table are integral part of the
  partitioned table.  A partition inherits identity columns from the
  partitioned table.  An identity column of a partition shares the
  identity space with the corresponding column of the partitioned
  table.  In other words, the same identity column across all
  partitions of a partitioned table share the same identity space.
  This is effected by sharing the same underlying sequence.
 
  When INSERTing directly into a partition, the sequence associated
  with the topmost partitioned table is used to calculate the value of
  the corresponding identity column.
 
  In regular inheritance, identity columns and their properties in a
  child table are independent of those in its parent tables.  A child
  table does not inherit identity columns or their properties
  automatically from the parent.  (This is unchanged.)
 
* Attached partition inherits identity column
 
  A table being attached as a partition inherits the identity property
  from the partitioned table.  This should be fine since we expect
  that the partition table's column has the same type as the
  partitioned table's corresponding column.  If the table being
  attached is a partitioned table, the identity properties are
  propagated down its partition hierarchy.
 
  An identity column in the partitioned table is also marked as NOT
  NULL.  The corresponding column in the partition needs to be marked
  as NOT NULL for the attach to succeed.
 
* Drop identity property when detaching partition
 
  A partition's identity column shares the identity space
  (i.e. underlying sequence) as the corresponding column of the
  partitioned table.  If a partition is detached it can longer share
  the identity space as before.  Hence the identity columns of the
  partition being detached loose their identity property.
 
  When identity of a column of a regular table is dropped it retains
  the NOT NULL constraint that came with the identity property.
  Similarly the columns of the partition being detached retain the NOT
  NULL constraints that came with identity property, even though the
  identity property itself is lost.
 
  The sequence associated with the identity property is linked to the
  partitioned table (and not the partition being detached).  That
  sequence is not dropped as part of detach operation.
 
* Partitions with their own identity columns are not allowed.
 
* The usual ALTER operations (add identity column, add identity
  property to existing column, alter properties of an indentity
  column, drop identity property) are supported for partitioned
  tables.  Changing a column only in a partitioned table or a
  partition is not allowed; the change needs to be applied to the
  whole partition hierarchy.
 
Author: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://www.postgresql.org/message-id/flat/CAExHW5uOykuTC+C6R1yDSp=o8Q83jr8xJdZxgPkxfZ1Ue5RRGg@mail.gmail.com

Continue reading Waiting for PostgreSQL 17 – Support identity columns in partitioned tables

Waiting for PostgreSQL 13 – Add logical replication support to replicate into partitioned tables

On 6th of April 2020, Peter Eisentraut committed patch:

Add logical replication support to replicate into partitioned tables 
 
Mainly, this adds support code in logical/worker.c for applying
replicated operations whose target is a partitioned table to its
relevant partitions.
 
Author: Amit Langote <amitlangote09@gmail.com>
Reviewed-by: Rafia Sabih <rafia.pghackers@gmail.com>
Reviewed-by: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Reviewed-by: Petr Jelinek <petr@2ndquadrant.com>
Discussion: https://www.postgresql.org/message-id/flat/CA+HiwqH=Y85vRK3mOdjEkqFK+E=ST=eQiHdpj43L=_eJMOOznQ@mail.gmail.com

Continue reading Waiting for PostgreSQL 13 – Add logical replication support to replicate into partitioned tables

Waiting for PostgreSQL 13 – pgbench: add –partitions and –partition-method options.

On 3rd of October 2019, Amit Kapila committed patch:

pgbench: add --partitions and --partition-method options.
 
These new options allow users to partition the pgbench_accounts table by
specifying the number of partitions and partitioning method.  The values
allowed for partitioning method are range and hash.
 
This feature allows users to measure the overhead of partitioning if any.
 
Author: Fabien COELHO
 
Alvaro Herrera
Discussion: https://postgr.es/m/alpine.DEB.2.21..7008@lancre

Continue reading Waiting for PostgreSQL 13 – pgbench: add –partitions and –partition-method options.

Waiting for PostgreSQL 12 – Support foreign keys that reference partitioned tables

On 3rd of April 2019, Alvaro Herrera committed patch:

Support foreign keys that reference partitioned tables
 
 
Previously, while primary keys could be made on partitioned tables, it
was not possible to define foreign keys that reference those primary
keys.  Now it is possible to do that.
 
Author: Álvaro Herrera
 
Discussion: https://postgr.es/m/20181102234158.735b3fevta63msbj@alvherre.pgsql

Continue reading Waiting for PostgreSQL 12 – Support foreign keys that reference partitioned tables

Migrating simple table to partitioned. How?

Recently someone asked, on irc, how to make table partitioned.

The thing is that it was supposed to be done with new partitioning, and not the old way.

The problem is that while we can create table that will be seen as partitioned – we can't alter table to become partitioned.

So. Is it possible?

Continue reading Migrating simple table to partitioned. How?

Foreign Key to partitioned table – part 2

Previously I wrote about how to create foreign key pointing to partitioned table.

Final solution in there required four separate functions and four triggers for each key between two tables.

Let's see how fast it is, and if it's possible to make it simpler.

Continue reading Foreign Key to partitioned table – part 2

Waiting for PostgreSQL 12 – Add pg_partition_tree to display information about partitions

On 30th of October 2018, Michael Paquier committed patch:

Add pg_partition_tree to display information about partitions
 
 
This new function is useful to display a full tree of partitions with a
partitioned table given in output, and avoids the need of any complex
WITH RECURSIVE query when looking at partition trees which are
deep multiple levels.
 
It returns a set of records, one for each partition, containing the
partition's name, its immediate parent's name, a boolean value telling
if the relation is a leaf in the tree and an integer telling its level
in the partition tree with given table considered as root, beginning at
zero for the root, and incrementing by one each time the scan goes one
level down.
 
Author: Amit Langote
 
Discussion: https://postgr.es/m/-9a51-ad02-d53e-@lab.ntt.co.jp

Continue reading Waiting for PostgreSQL 12 – Add pg_partition_tree to display information about partitions