Date: Sat, 14 Mar 2020 15:42:20 -0400
From: Bruce Momjian <bruce@momjian.us>
To: tanay.purnaye@gmail.com, pgsql-docs@lists.postgresql.org
Subject: Re: Examples required in || 5.10. Table Partitioning
Message-ID: <20200314194220.GA22336@momjian.us>
References: <158099182679.1093.11650509001908549339@wrigleys.postgresql.org>
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On Thu, Feb  6, 2020 at 12:23:46PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/12/ddl-partitioning.html
> Description:
> 
> Hello ,
> 
> As I'm searching for the official documentation of Hash Partition and List
> Partition with example with more description the only information is found
> is  as below :
> 
> List Partitioning
> The table is partitioned by explicitly listing which key values appear in
> each partition.
> 
> Hash Partitioning
> The table is partitioned by specifying a modulus and a remainder for each
> partition. Each partition will hold the rows for which the hash value of the
> partition key divided by the specified modulus will produce the specified
> remainder.
> 
> But how to create and manage these above 2 partition is not explained in
> documentation properly officially.for further information related to these 2
> partition we need to search private blogs,because of lack of information
> provided in the documentation 5.10. Table Partitioning I only saw the Range
> partition example throughout the Table Partitioning .
> 
> I request you to modify the 5.10. Table Partitioning section and make it
> more informative as Table Partition is very important in PostgreSQL .

Well, there are examples in the CREATE TABLE manual page:

	https://www.postgresql.org/docs/12/sql-createtable.html

	When creating a hash partition, a modulus and remainder must be
	specified. The modulus must be a positive integer, and the remainder
	must be a non-negative integer less than the modulus. Typically, when
	initially setting up a hash-partitioned table, you should choose a
	modulus equal to the number of partitions and assign every table the
	same modulus and a different remainder (see examples, below). However,
	it is not required that every partition have the same modulus, only that
	every modulus which occurs among the partitions of a hash-partitioned
	table is a factor of the next larger modulus. This allows the number of
	partitions to be increased incrementally without needing to move all the
	data at once. For example, suppose you have a hash-partitioned table
	with 8 partitions, each of which has modulus 8, but find it necessary to
	increase the number of partitions to 16. You can detach one of the
	modulus-8 partitions, create two new modulus-16 partitions covering the
	same portion of the key space (one with a remainder equal to the
	remainder of the detached partition, and the other with a remainder
	equal to that value plus 8), and repopulate them with data. You can then
	repeat this -- perhaps at a later time -- for each modulus-8 partition
	until none remain. While this may still involve a large amount of data
	movement at each step, it is still better than having to create a whole
	new table and move all the data at once.

	CREATE TABLE orders (
	    order_id     bigint not null,
	    cust_id      bigint not null,
	    status       text
	) PARTITION BY HASH (order_id);

	CREATE TABLE orders_p1 PARTITION OF orders
	    FOR VALUES WITH (MODULUS 4, REMAINDER 0);
	CREATE TABLE orders_p2 PARTITION OF orders
	    FOR VALUES WITH (MODULUS 4, REMAINDER 1);
	CREATE TABLE orders_p3 PARTITION OF orders
	    FOR VALUES WITH (MODULUS 4, REMAINDER 2);
	CREATE TABLE orders_p4 PARTITION OF orders
	    FOR VALUES WITH (MODULUS 4, REMAINDER 3);


	CREATE TABLE cities (
	    city_id      bigserial not null,
	    name         text not null,
	    population   bigint
	) PARTITION BY LIST (left(lower(name), 1));

	CREATE TABLE cities_ab
	    PARTITION OF cities (
	    CONSTRAINT city_id_nonzero CHECK (city_id != 0)
	) FOR VALUES IN ('a', 'b');

Is that sufficient?

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +