Postgresql partition into a fixed set of files by ID - sql

Question

Apache Spark has the option to split into multiple files with the bucketBy command. For example if I have 100 million user IDs, I can split the table into 32 different files, where some type of hashing algorithm is used to distribute and lookup the data between files.
Can Postgres split tables into a fixed number of partitions somehow? If it's not a native feature can it still be accomplished, for example generate a hash; turn hash into a number; take modulo % 32 as parititon range.

Answer 1

example with modulo:
a short partitions setup:
db=# create table p(i int);
CREATE TABLE
db=# create table p1 ( check (mod(i,3)=0) ) inherits (p);
CREATE TABLE
db=# create table p2 ( check (mod(i,3)=1) ) inherits (p);
CREATE TABLE
db=# create table p3 ( check (mod(i,3)=2) ) inherits (p);
CREATE TABLE
db=# create rule pir3 AS ON insert to p where mod(i,3) = 2 do instead insert into p3 values (new.*);
CREATE RULE
db=# create rule pir2 AS ON insert to p where mod(i,3) = 1 do instead insert into p2 values (new.*);
CREATE RULE
db=# create rule pir1 AS ON insert to p where mod(i,3) = 0 do instead insert into p1 values (new.*);
CREATE RULE
checking:
db=# insert into p values (1),(2),(3),(4),(5);
INSERT 0 0
db=# select * from p;
i
---
3
1
4
2
5
(5 rows)
db=# select * from p1;
i
---
3
(1 row)
db=# select * from p2;
i
---
1
4
(2 rows)
db=# select * from p3;
i
---
2
5
(2 rows)
https://www.postgresql.org/docs/current/static/tutorial-inheritance.html
https://www.postgresql.org/docs/current/static/ddl-partitioning.html
and demo of partitions working:
db=# explain analyze select * from p where mod(i,3) = 2;
QUERY PLAN
----------------------------------------------------------------------------------------------------
Append (cost=0.00..48.25 rows=14 width=4) (actual time=0.013..0.015 rows=2 loops=1)
-> Seq Scan on p (cost=0.00..0.00 rows=1 width=4) (actual time=0.004..0.004 rows=0 loops=1)
Filter: (mod(i, 3) = 2)
-> Seq Scan on p3 (cost=0.00..48.25 rows=13 width=4) (actual time=0.009..0.011 rows=2 loops=1)
Filter: (mod(i, 3) = 2)
Planning time: 0.203 ms
Execution time: 0.052 ms
(7 rows)