Horton

Re: Some regular-expression performance hacking

Joel Jacobson <joel@compiler.org>

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From: "Joel Jacobson" <joel@compiler.org>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@lists.postgresql.org
Date: 2021-02-19T12:45:34Z
Lists: pgsql-hackers 
On Thu, Feb 18, 2021, at 19:53, Tom Lane wrote:
>(Having said that, I can't help noticing that a very large fraction
>of those usages look like, eg, "[\w\W]".  It seems to me that that's
>a very expensive and unwieldy way to spell ".".  Am I missing
>something about what that does in Javascript?)

This popular regex

    ^(?:\s*(<[\w\W]+>)[^>]*|#([\w-]+))$

is coming from jQuery:

// A simple way to check for HTML strings
// Prioritize #id over <tag> to avoid XSS via location.hash (#9521)
// Strict HTML recognition (#11290: must start with <)
// Shortcut simple #id case for speed
rquickExpr = /^(?:\s*(<[\w\W]+>)[^>]*|#([\w-]+))$/,

From: https://code.jquery.com/jquery-3.5.1.js

I think this is a non-POSIX hack to match any character, including newlines,
which are not included unless the "s" flag is set.

Javascript test:

"foo\nbar".match(/(.+)/)[1];
"foo"

"foo\nbar".match(/(.+)/s)[1];
"foo
bar"

"foo\nbar".match(/([\w\W]+)/)[1];
"foo
bar"

/Joel

Commits

  1. Suppress unnecessary regex subre nodes in a couple more cases.

  2. Improve memory management in regex compiler.

  3. Extend a test case a little

  4. Allow complemented character class escapes within regex brackets.

  5. Suppress compiler warning in new regex match-all detection code.

  6. Avoid generating extra subre tree nodes for capturing parentheses.

  7. Convert regex engine's subre tree from binary to N-ary style.

  8. Fix regex engine to suppress useless concatenation sub-REs.

  9. Recognize "match-all" NFAs within the regex engine.

  10. Invent "rainbow" arcs within the regex engine.

  11. Make some minor improvements in the regex code.

  12. Display the time when the process started waiting for the lock, in pg_locks, take 2

  13. README/C-comment: document GiST's NSN value

  14. doc: Mention NO DEPENDS ON EXTENSION in its supported ALTER commands