Improve performance of fixempties() pass in regular-expression compiler. The previous coding took something like O(N^4) time to fully process a chain of N EMPTY arcs. We can't really do much better than O(N^2) because we have to insert about that many arcs, but we can do lots better than what's there now. The win comes partly from using mergeins() to amortize de-duplication of arcs across multiple source states, and partly from exploiting knowledge of the ordering of arcs for each state to avoid looking at arcs we don't need to consider during the scan. We do have to be a bit careful of the possible reordering of arcs introduced by the sort-merge coding of the previous commit, but that's not hard to deal with.
Back-patch to all supported branches. Branch ------ master Details ------- http://git.postgresql.org/pg/commitdiff/f5b7d103bc4a97a64f9e8ca83192a96767d9a34c Modified Files -------------- src/backend/regex/regc_nfa.c | 249 +++++++++++++++++++++--------------------- src/backend/regex/regcomp.c | 6 +- 2 files changed, 128 insertions(+), 127 deletions(-) -- Sent via pgsql-committers mailing list ([email protected]) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-committers
