Re: POSIX regex performance bug in 7.3 Vs. 7.2

Proof of concept:

PG 7.3 using regression database:

regression=# select count(*) from tenk1 where 'quotidian' ~ string4;count
-------    0
(1 row)

Time: 676.14 ms
regression=# select count(*) from tenk1 where 'quotidian' ~ stringu1;count
-------    0
(1 row)

Time: 3426.96 ms
regression=# select count(*) from tenk1 where 'quotidian' ~* stringu1;count
-------    0
(1 row)

Time: 466344.48 ms


CVS tip plus code extracted from Tcl:

regression=# select count(*) from tenk1 where 'quotidian' ~ string4;count
-------    0
(1 row)

Time: 472.48 ms
regression=# select count(*) from tenk1 where 'quotidian' ~ stringu1;count
-------    0
(1 row)

Time: 4414.91 ms
regression=# select count(*) from tenk1 where 'quotidian' ~* stringu1;count
-------    0
(1 row)

Time: 4608.49 ms

In the first case there are only four distinct patterns used, so we're
running with cached precompiled regexes.  In the other cases a new regex
compilation must occur at each row.  So, regex execution is a little
faster than before (at least for trivial regexes); compilation seems to
be a shade slower, but it doesn't fall over and die when compiling
case-insensitive patterns (or bracket expressions, which is what the
code actually reduces a case-insensitive pattern to).

This is nowhere near ready to commit, but it compiles cleanly and passes
regression tests ...
        regards, tom lane