Horton

Re: Compressed TOAST Slicing

Daniel Verite <daniel@manitou-mail.org>

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From: "Daniel Verite" <daniel@manitou-mail.org>
To: "Paul Ramsey" <pramsey@cleverelephant.ca>
Cc: "Simon Riggs" <simon@2ndquadrant.com>,rafia.sabih@enterprisedb.com,"Tom Lane" <tgl@sss.pgh.pa.us>,"Stephen Frost" <sfrost@snowman.net>,"PostgreSQL Hackers" <pgsql-hackers@lists.postgresql.org>
Date: 2019-02-20T18:50:07Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Add support for partial TOAST decompression

  2. Remove remaining hard-wired OID references in the initial catalog data.

  3. Rephrase references to "time qualification".

	Paul Ramsey wrote:

> Oddly enough, I couldn't find many/any things that were sensitive to
> left-end decompression. The only exception is "LIKE this%" which
> clearly would be helped, but unfortunately wouldn't be a quick
> drop-in, but a rather major reorganization of the regex handling.

What about starts_with(string, prefix)?

text_starts_with(arg1,arg2) in varlena.c does a full decompression
of  arg1 when it could limit itself to the length of the smaller arg2:

Datum
text_starts_with(PG_FUNCTION_ARGS)
....
  len1 = toast_raw_datum_size(arg1);
  len2 = toast_raw_datum_size(arg2);
  if (len2 > len1)
      result = false;
  else
  {
      text	 *targ1 = DatumGetTextPP(arg1);
      text	 *targ2 = DatumGetTextPP(arg2);

      result = (memcmp(VARDATA_ANY(targ1), VARDATA_ANY(targ2),
	       VARSIZE_ANY_EXHDR(targ2)) == 0);
...



Best regards,
-- 
Daniel Vérité
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Twitter: @DanielVerite