Re: Compressed TOAST Slicing

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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