imitatio creatio

Rafal Pietrak asked a question about postgres performance in partitioning scenarios.

The problem is, in classical partitioning approach you decide into which partition put the data basing only on the inserted data itself.

But we consider also situation when you want to make this decision basing on current database content.

For example we have some “driving” or “routing” table which tells us which partition is currently active.

Please read the above post for more background.

I prepared 4 test cases, for all combinations of rule versus trigger and static versus dynamic aka table-driven partitioning.

Test was performed on PostgreSQL 8.3.3 on Linux, commodity desktop box.

To make things short, here are the results of two test runs (links point to test scripts):
/what is measured: INSERT of 10000 rows/

Partitioning with RULEs, no dynamic routing:
2444.293 ms 2516.314 ms

Partitioning with RULEs, with dynamic routing:
42380.037 ms 39248.666 ms

Partitioning with TRIGGER, no dynamic routing:
14512.787 ms 14669.310 ms

Partitioning with TRIGGER, with dynamic routing:
13486.808 ms 13904.370 ms

Conclusion:

If you have to do some database lookup to decide which partition data belongs to, use a trigger on master table.
If you have a well defined static set of rules, use PostgreSQL rule system.

hstore is a “Lazy DBA” extension for postgres, which enables storing hash tables in a table column.

When using hstore, sometimes you want to rename hash keys.


#
# create function renamekey( _hstore hstore, _oldname text, _newname text ) returns hstore as
$$ select delete($1, $2) || ($3 => ($1 -> $2)) $$ language sql immutable strict;
#
# \set old_codename '''dizzyflag'''
# \set new_codename '''is_trade'''
#
# UPDATE table_with_hstore
SET flags = renamekey(flags, :old_codename, :new_codename)
WHERE (flags -> :old_codename) is not null;
#


Jarek napisał ciekawy artykuł o sortowaniu napisów w PostgreSQL (i nie tylko, w zasadzie rzecz dotyczy localesów w glibc).

Same as depesz and Greg, but using user-defined function:


CREATE FUNCTION ea_totals(text) RETURNS text AS $body$
my $result;
my $com = shift;
$com =~ /^\s*explain\s+/i or die qq{Not an explain query\n};
my $rv = spi_exec_query($com);
$rv->{status} eq 'SPI_OK_UTILITY' or die qq{Not a proper explain?\n};
for (map { $_->{'QUERY PLAN'} } @{$rv->{rows}}) {
my $string = ' ' x 10;
if ( /actual time=\d+\.\d*\.\.(\d+\.\d*) rows=\d+ loops=(\d+)/ ) {
$string = sprintf("%10.1f", $1 * $2);
}
$result .= "$string $_ \n";
}
return $result;
$body$ LANGUAGE plperl;


Usage:

SELECT * FROM ea_totals( $$ explain analyze query here $$);