VIM for Programmers
OK, this one is originally called "Vim for (PHP) Programmers".
But (1) it has not much to do with PHP, and (2) it is such a pearl I have to share it.
See this on scribd: VIM for PHP Programmers.
I use Vim for about 5 years now, and I discovered that I'm just a rookie :)
Postgres partitioning performance – rules vs triggers
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.
variable length positive lookbehind in perl regex
perlre says it does not support lookbehind matches with arbitrary length.
here is a workaround
#!perl -l -w
use strict;
#
print my $txt = 'Alice has a fish. It is a nice fish.
Bob has a dog. John has a cat.
Line 3 is not important.
Filip has a perl.
---------------------------';
#
=pod WE WANT THIS but this gives Perl error.
while ( $txt =~ m{(?<=$behind_re)($match_re)(?=$ahead_re)}g ) {
print $&;
}
=cut
#
my $behind_re = qr/[A-Z][a-z]+ has a /; # Filip has a
my $match_re = qr/\w+/i; # perl
my $ahead_re = qr/\./; # .
#
while ( $txt =~ m{($behind_re)}g ) { # we look for behind match globally,
if ( $txt =~ m{\G($match_re)(?=$ahead_re)} ) { # we search for the rest anchored at each found position
print $&; # voila
}
}
#
