Improve SIMILAR TO performance
------------------------------
Key: CORE-3919
URL: http://tracker.firebirdsql.org/browse/CORE-3919
Project: Firebird Core
Issue Type: Improvement
Affects Versions: 3.0 Initial
Reporter: Adriano dos Santos Fernandes
There is two tickets (CORE-3773 and CORE-3858) about SIMILAR TO performance.
Both are related to the algorithm (NFA-based, without heuristics) used, which
may cause exponential backtracking for special patterns and/or long texts.
The improvement performance of this ticket is about re-implementation of the
current algorithm.
With test from CORE-3858, time decreases from 165 seconds to 101 seconds.
Times in seconds for test: echo "set stats on; select
iif('aaaaaaaaaaabaaaaaabaaaaaaaaaab' SIMILAR TO '(a+b?)+a+' escape '\', 1, 0)
from rdb\$database;" | isql -q t.fdb
(iterative version is the one used, and recursive version is deactivated due to
stack overflow problems)
Before:
gcc iterative: 11,83
gcc recursive: 4,74
clang iterative: 9,73
clang recursive: 3,45
After:
gcc iterative: 5,54
gcc recursive: 3,97
clang iterative: 3,85
clang recursive: 3,69
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