9 Commits (f80049f76a32858601510eaaef19ab8160e4c9b3)

Author	SHA1	Message	Date
Bruce Momjian	ee94300446	Update copyright for 2016 ... Backpatch certain files through 9.1	10 years ago
Tom Lane	12c9a04008	Implement lookbehind constraints in our regular-expression engine. ... A lookbehind constraint is like a lookahead constraint in that it consumes no text; but it checks for existence (or nonexistence) of a match *ending* at the current point in the string, rather than one *starting* at the current point. This is a long-requested feature since it exists in many other regex libraries, but Henry Spencer had never got around to implementing it in the code we use. Just making it work is actually pretty trivial; but naive copying of the logic for lookahead constraints leads to code that often spends O(N^2) time to scan an N-character string, because we have to run the match engine from string start to the current probe point each time the constraint is checked. In typical use-cases a lookbehind constraint will be written at the start of the regex and hence will need to be checked at every character --- so O(N^2) work overall. To fix that, I introduced a third copy of the core DFA matching loop, paralleling the existing longest() and shortest() loops. This version, matchuntil(), can suspend and resume matching given a couple of pointers' worth of storage space. So we need only run it across the string once, stopping at each interesting probe point and then resuming to advance to the next one. I also put in an optimization that simplifies one-character lookahead and lookbehind constraints, such as "(?=x)" or "(?<!\w)", into AHEAD and BEHIND constraints, which already existed in the engine. This avoids the overhead of the LACON machinery entirely for these rather common cases. The net result is that lookbehind constraints run a factor of three or so slower than Perl's for multi-character constraints, but faster than Perl's for one-character constraints ... and they work fine for variable-length constraints, which Perl gives up on entirely. So that's not bad from a competitive perspective, and there's room for further optimization if anyone cares. (In reality, raw scan rate across a large input string is probably not that big a deal for Postgres usage anyway; so I'm happy if it's linear.)	10 years ago
Tom Lane	9f1e642d50	Fix incorrect handling of lookahead constraints in pg_regprefix(). ... pg_regprefix was doing nothing with lookahead constraints, which would be fine if it were the right kind of nothing, but it isn't: we have to terminate our search for a fixed prefix, not just pretend the LACON arc isn't there. Otherwise, if the current state has both a LACON outarc and a single plain-color outarc, we'd falsely conclude that the color represents an addition to the fixed prefix, and generate an extracted index condition that restricts the indexscan too much. (See added regression test case.) Terminating the search is conservative: we could traverse the LACON arc (thus assuming that the constraint can be satisfied at runtime) and then examine the outarcs of the linked-to state. But that would be a lot more work than it seems worth, because writing a LACON followed by a single plain character is a pretty silly thing to do. This makes a difference only in rather contrived cases, but it's a bug, so back-patch to all supported branches.	10 years ago
Bruce Momjian	4baaf863ec	Update copyright for 2015 ... Backpatch certain files through 9.0	11 years ago
Bruce Momjian	0a78320057	pgindent run for 9.4 ... This includes removing tabs after periods in C comments, which was applied to back branches, so this change should not effect backpatching.	12 years ago
Bruce Momjian	7e04792a1c	Update copyright for 2014 ... Update all files in head, and files COPYRIGHT and legal.sgml in all back branches.	12 years ago
Bruce Momjian	9af4159fce	pgindent run for release 9.3 ... This is the first run of the Perl-based pgindent script. Also update pgindent instructions.	13 years ago
Bruce Momjian	bd61a623ac	Update copyrights for 2013 ... Fully update git head, and update back branches in ./COPYRIGHT and legal.sgml files.	13 years ago
Tom Lane	628cbb50ba	Re-implement extraction of fixed prefixes from regular expressions. ... To generate btree-indexable conditions from regex WHERE conditions (such as WHERE indexed_col ~ '^foo'), we need to be able to identify any fixed prefix that a regex might have; that is, find any string that must be a prefix of all strings satisfying the regex. We used to do that with entirely ad-hoc code that looked at the source text of the regex. It didn't know very much about regex syntax, which mostly meant that it would fail to identify some optimizable cases; but Viktor Rosenfeld reported that it would produce actively wrong answers for quantified parenthesized subexpressions, such as '^(foo)?bar'. Rather than trying to extend the ad-hoc code to cover this, let's get rid of it altogether in favor of identifying prefixes by examining the compiled form of a regex. To do this, I've added a new entry point "pg_regprefix" to the regex library; hopefully it is defined in a sufficiently general fashion that it can remain in the library when/if that code gets split out as a standalone project. Since this bug has been there for a very long time, this fix needs to get back-patched. However it depends on some other recent commits (particularly the addition of wchar-to-database-encoding conversion), so I'll commit this separately and then go to work on back-porting the necessary fixes.	14 years ago