Waiting for PostgreSQL 11 – Add hash partitioning.

On 9th of November 2017, Robert Haas committed patch:

Add hash partitioning.
 
Hash partitioning is useful when you want to partition a growing data
set evenly.  This can be useful to keep table sizes reasonable, which
makes maintenance operations such as VACUUM faster, or to enable
partition-wise join.
 
At present, we still depend on constraint exclusion for partitioning
pruning, and the shape of the partition constraints for hash
partitioning is such that that doesn't work.  Work is underway to fix
that, which should both improve performance and make partitioning
pruning work with hash partitioning.
 
Amul Sul, reviewed and tested by Dilip Kumar, Ashutosh Bapat, Yugo
Nagata, Rajkumar Raghuwanshi, Jesper Pedersen, and by me.  A few
final tweaks also by me.
 
Discussion: http://postgr.es/m/CAAJ_b96fhpJAP=ALbETmeLk1Uni_GFZD938zgenhF49qgDTjaQ@mail.gmail.com

Continue reading Waiting for PostgreSQL 11 – Add hash partitioning.

Waiting for PostgreSQL 10 – hash indexing vs. WAL

For a long time hash indexed were not crash safe, and couldn't be used on replication slave, because they skipped WAL. Now, thanks to these two commits, it has changed:

On 14th of March 2017, Robert Haas committed patch:

hash: Add write-ahead logging support.
 
The warning about hash indexes not being write-ahead logged and their
use being discouraged has been removed.  "snapshot too old" is now
supported for tables with hash indexes.  Most importantly, barring
bugs, hash indexes will now be crash-safe and usable on standbys.
 
This commit doesn't yet add WAL consistency checking for hash
indexes, as we now have for other index types; a separate patch has
been submitted to cure that lack.
 
Amit Kapila, reviewed and slightly modified by me.  The larger patch
series of which this is a part has been reviewed and tested by Álvaro
Herrera, Ashutosh Sharma, Mark Kirkwood, Jeff Janes, and Jesper
Pedersen.
 
Discussion: http://postgr.es/m/CAA4eK1JOBX=YU33631Qh-XivYXtPSALh514+jR8XeD7v+K3r_Q@mail.gmail.com

and then, ~ 13 hours later, Robert committed also:

hash: Support WAL consistency checking.
 
Kuntal Ghosh, reviewed by Amit Kapila and Ashutosh Sharma, with
a few tweaks by me.
 
Discussion: http://postgr.es/m/CAGz5QCJLERUn_zoO0eDv6_Y_d0o4tNTMPeR7ivTLBg4rUrJdwg@mail.gmail.com

Continue reading Waiting for PostgreSQL 10 – hash indexing vs. WAL

Explaining the unexplainable – part 3

In previous post in the series I wrote about how to interpret single line in explain analyze output, it's structure, and later on described all basic data-getting operations (nodes in explain tree).

Today, we'll move towards more complicated operations.

Continue reading Explaining the unexplainable – part 3

Waiting for 9.1 – Arrays in PL/Perl

On 18th of February, Alvaro Herrera committed patch:

Convert Postgres arrays to Perl arrays on PL/perl input arguments
 
More generally, arrays are turned in Perl array references, and row and
composite types are turned into Perl hash references.  This is done
recursively, in a way that's natural to every Perl programmer.
 
To avoid a backwards compatibility hit, the string representation of
each structure is also available if the function requests it.
 
Authors: Alexey Klyukin and Alex Hunsaker.
Some code cleanups by me.

Continue reading Waiting for 9.1 – Arrays in PL/Perl

Should you use HASH index?

Today, Mattias|farm on IRC asked how to create primary key using HASH index. After some talk, he said that in some books it said that for “=" (equality) hash indexes are better.

So, I digged a bit deeper.

IMPORTANT UPDATE: As of PostgreSQL 10 hash indexes are WAL logged. As such, main point against them is gone.

Continue reading Should you use HASH index?

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Tag: hash