Hi, On Thu, Jun 25, 2026 at 11:28 AM Masahiko Sawada <[email protected]> wrote: > > Since commit ec8719ccbfcd made hex_decode_safe() SIMD-aware, decoding > a run of hex digits is now fast. The attached patch reuses > hex_decode_safe() in the UUID input function to speed up parsing. > > We accept several textual forms of a UUID[1]. The fast path handles > the common ones: 32 hex digits, the canonical 8x-4x-4x-4x-12x form > (where "nx" means n hex digits), and either of those wrapped in > braces. Otherwise, it falls back to the ordinary scalar UUID parse. > > I've benchmarked the parse speed using the following query: > > CREATE TEMP TABLE u AS SELECT gen_random_uuid()::text AS t FROM > generate_series(1, 1000000); > EXPLAIN (ANALYZE, TIMING OFF) SELECT t::uuid FROM u; > > I compared the execution time of the second query, which measures > uuid_in() alone, with/without SIMD optimization. Here are results (the > median of 5 runs): > > HEAD: 208.879 ms > Patched: 40.983 ms
Nice! > The improvements look promising to me. But in a realistic pipeline the > parse is a small fraction of the work, so end-to-end gains could be > much smaller. > > Feedback is very welcome. I had a quick look at the patch. It mostly looks good to me. I like the idea of falling back to the scalar path when an error occurs - a neat user experience. I think it's not worth adding a test case for this because I believe this code gets covered anyway from existing tests. A few comments: 1/ + * pass the local esctx instead of escontext to hex_decode_safe() to Instead of using variable names in the comments, let's say something like: we pass a separate error context to detect errors in the SIMD path and fall back to the normal path instead of raising ERRORs, for a better user experience. 2/ + if (esctx.error_occurred) + string_to_uuid_scalar(source, uuid, escontext); An error on supported platforms seems rare, but when one occurs, I think it's worth emitting a WARNING or LOG message. This way the query succeeds, but later in the server logs, if noticed, it could provide useful reasoning or uncover issues in the SIMD code. -- Bharath Rupireddy Amazon Web Services: https://aws.amazon.com
