pgsql: Use hex_decode_safe() to speed up UUID input.

Use hex_decode_safe() to speed up UUID input.

Previously, string_to_uuid() decoded one byte at a time, calling
isxdigit() twice and strtoul() once for every pair of hexadecimal
digits. Commit ec8719ccbfcd made hex_decode_safe() decode a run of
hexadecimal digits in bulk, so add a fast path for the two common
shapes: 32 contiguous hexadecimal digits, and the canonical
8x-4x-4x-4x-12x form, each optionally wrapped in braces.

Anything else, and any decoding error, falls back to the
byte-at-a-time parser, so the accepted grammar and the error messages
don't change. hex_decode_safe() also skips whitespace, which the UUID
grammar forbids, so we treat a short decode as an error too. Rejecting
an input that has a fast-path shape therefore costs a second
parse. But this only happens for syntax-error cases, so it's not a
problem in practice.

Reviewed-by: Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>
Reviewed-by: Haibo Yan <tristan(dot)yim(at)gmail(dot)com>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: John Naylor <johncnaylorls(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAD21AoCqeR4UQU77Q_yOMNNzJ7AVeiO5QZT+4HnzPm4Wm-e02Q@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/72af14bccd2127bf20ddeaf198b78de46e9e892b

Modified Files
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src/backend/utils/adt/uuid.c | 101 +++++++++++++++++++++++++++++++++++--
src/test/regress/expected/uuid.out | 74 +++++++++++++++++++++++++++
src/test/regress/sql/uuid.sql | 24 +++++++++
3 files changed, 194 insertions(+), 5 deletions(-)