Postgresql – enabling fsync in postgresql 9.1

You will need to assign ownership of the table to the group the two users have in common.

Demo:

Setup:

CREATE ROLE thegroup;
CREATE USER user1 IN ROLE thegroup;
CREATE USER user2 IN ROLE thegroup;
CREATE TABLE t1 ( x integer not null );
ALTER TABLE t1 OWNER TO user1;

Without further changes, here's what happens if user2 tries to add an index on t1.x:

regress=# SET ROLE user2;
SET
regress=> CREATE INDEX t1_x_idx ON t1(x);
ERROR:  must be owner of relation t1

The solution is to grant the table ownership to the shared role. As user1 or a superuser:

ALTER TABLE t1 OWNER TO thegroup;

now:

regress=# SET ROLE user2;
SET
regress=> CREATE INDEX t1_x_idx ON t1(x);
CREATE INDEX
regress=> 

After asking on pgsql-performance list, Jeff Janes figured out that the cause was associated to the default collation used by Postgres (see this link for more informations). MacMini was using the much performing collation while Dell T420 was using the en/US collation.

T420 (Postgres 9.4.1)

                                  List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    |   Access privileges   
-----------+----------+----------+-------------+-------------+-----------------------
 pen       | pen      | UTF8     | en_US.UTF-8 | en_US.UTF-8 | 
 postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | 
 template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
 template1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
(4 rows)

MacMini (Postgres 9.0.13)

                                    List of databases
       Name        |   Owner    | Encoding | Collation | Ctype |    Access privileges    
-------------------+------------+----------+-----------+-------+-------------------------
 caldav            | caldav     | UTF8     | C         | C     | 
 collab            | collab     | UTF8     | C         | C     | 
 device_management | _devicemgr | UTF8     | C         | C     | 
 pen               | pen        | UTF8     | C         | C     | 
 postgres          | _postgres  | UTF8     | C         | C     | 
 roundcubemail     | roundcube  | UTF8     | C         | C     | 
 template0         | _postgres  | UTF8     | C         | C     | =c/_postgres           +
                   |            |          |           |       | _postgres=CTc/_postgres
 template1         | _postgres  | UTF8     | C         | C     | =c/_postgres           +
                   |            |          |           |       | _postgres=CTc/_postgres
(8 rows)

After setting collation on T420 "C" the A transaction went from 195 seconds to 33 seconds against 40 seconds on Mac Mini; B type transaction went from 141 seconds to 78 seconds against 101 seconds on Mac Mini. This is the best performance improvement after modifing BIOS settings. Many kernel adjustments didn't provide significant improvements.

So, running the following command will initialize a new database with collation C and encoding UTF8:

/usr/local/pgsql/bin/initdb -D /path/to/your/data --no-locale --encoding=UTF8

I hope this post will help other people in the future. After reading about a lot of digressions about kernel, virtual memory, RAID controllers, disk cache, WAL and other tech stuff I never found someone talking about collations.