On Mon, Aug 17, 2026 at 3:21 PM Masahiko Sawada <[email protected]> wrote:
> On Fri, Aug 14, 2026 at 6:08 PM Masahiko Sawada <[email protected]> > wrote: > > > > On Fri, Aug 14, 2026 at 4:33 PM Masahiko Sawada <[email protected]> > wrote: > > > > > > On Thu, Aug 6, 2026 at 8:07 PM Chao Li <[email protected]> wrote: > > > > > > > > > > > > > > > > > On Aug 7, 2026, at 00:09, Masahiko Sawada <[email protected]> > wrote: > > > > > > > > > > On Wed, Aug 5, 2026 at 8:40 PM Chao Li <[email protected]> > wrote: > > > > >> > > > > >> > > > > >> > > > > >>> On Aug 6, 2026, at 08:19, Masahiko Sawada <[email protected]> > wrote: > > > > >>> > > > > >>> On Tue, Jun 30, 2026 at 11:03 AM Haibo Yan < > [email protected]> wrote: > > > > >>>> > > > > >>>> On Tue, Jun 30, 2026 at 10:53 AM Masahiko Sawada < > [email protected]> wrote: > > > > >>>>> > > > > >>>>> On Mon, Jun 29, 2026 at 5:53 PM Haibo Yan < > [email protected]> wrote: > > > > >>>>>> > > > > >>>>>> On Mon, Jun 29, 2026 at 2:55 PM Masahiko Sawada < > [email protected]> wrote: > > > > >>>>>>> > > > > >>>>>>> On Sun, Jun 28, 2026 at 7:20 PM Haibo Yan < > [email protected]> wrote: > > > > >>>>>>>> > > > > >>>>>>>> On Thu, Jun 25, 2026 at 3:16 PM Masahiko Sawada < > [email protected]> wrote: > > > > >>>>>>>>> > > > > >>>>>>>>> On Thu, Jun 25, 2026 at 2:31 PM Haibo Yan < > [email protected]> wrote: > > > > >>>>>>>>>> > > > > >>>>>>>>>> > > > > >>>>>>>>>> > > > > >>>>>>>>>> On Thu, Jun 25, 2026 at 11:28 AM Masahiko Sawada < > [email protected]> wrote: > > > > >>>>>>>>>>> > > > > >>>>>>>>>>> Hi all, > > > > >>>>>>>>>>> > > > > >>>>>>>>>>> I'd like to propose the $subject. > > > > >>>>>>>>>>> > > > > >>>>>>>>>>> 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 > > > > >>>>>>>>>>> > > > > >>>>>>>>>>> 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 may be missing something, but I wonder whether the fast > path is relying on > > > > >>>>>>>>>> slightly different input semantics from the existing UUID > parser. > > > > >>>>>>>>>> > > > > >>>>>>>>>> In particular, hex_decode_safe() is not a strict “32 hex > characters only” > > > > >>>>>>>>>> decoder. It skips whitespace, which is fine for its > existing callers, but I > > > > >>>>>>>>>> don’t think UUID input should treat whitespace inside the > UUID body as > > > > >>>>>>>>>> ignorable. > > > > >>>>>>>>> > > > > >>>>>>>>> Good catch! hex_decode_safe() skips whitespaces so the > patch accepts > > > > >>>>>>>>> the following UUID value, which is bad: > > > > >>>>>>>>> > > > > >>>>>>>>> select '019f00b5-7f8a-722f-b707-59f0ed25cd '::uuid; > > > > >>>>>>>>> uuid > > > > >>>>>>>>> -------------------------------------- > > > > >>>>>>>>> 019f00b5-7f8a-722f-b707-59f0ed25cd00 > > > > >>>>>>>>> (1 row) > > > > >>>>>>>>> > > > > >>>>>>>>>> Also, since hex_decode_safe() returns void, the UUID fast > path > > > > >>>>>>>>>> cannot verify that exactly UUID_LEN bytes were produced. > > > > >>>>>>>>> > > > > >>>>>>>>> IIUC hex_decode_safe() does return the output length in > bytes. So I > > > > >>>>>>>>> think we can fallback to the scalar UUID parser if > > > > >>>>>>>>> esctx.error_occurred is true or if the returned value is > not 16. > > > > >>>>>>>>> > > > > >>>>>>>> > > > > >>>>>>>> You’re right, I misread that part. Checking both > esctx.error_occurred and > > > > >>>>>>>> the returned length sounds good to me. > > > > >>>>>>>> > > > > >>>>>>>>>> > > > > >>>>>>>>>> So I think it would be safer either to pre-validate that > the 32 source > > > > >>>>>>>>>> characters are all hex digits before calling > hex_decode_safe(), or to use a > > > > >>>>>>>>>> UUID-specific strict hex decoder for this path. After > that, a comment > > > > >>>>>>>>>> explaining why hex_decode_safe() is safe here would make > the invariant much > > > > >>>>>>>>>> clearer. > > > > >>>>>>>>> > > > > >>>>>>>>> IIUC hex_decode_simd_helper() accepts only hex digits so > we could > > > > >>>>>>>>> re-use it for UUID parsing. Let me check if the above idea > of using > > > > >>>>>>>>> the return value works for us first. > > > > >>>>>>>>> > > > > >>>>>>>> > > > > >>>>>>>> That sounds reasonable. My main concern was to keep the > fast path’s accepted > > > > >>>>>>>> input set identical to the scalar UUID parser. Falling > back when the decoded > > > > >>>>>>>> length is not UUID_LEN, together with regression tests for > whitespace cases, > > > > >>>>>>>> should address that. > > > > >>>>>>>> > > > > >>>>>>>>>> > > > > >>>>>>>>>> Could you also add a few regression tests for invalid > inputs that contain > > > > >>>>>>>>>> whitespace inside otherwise fast-path-looking UUID > strings? For example: > > > > >>>>>>>>>> > > > > >>>>>>>>>> > --------------------------------------------------------------- > > > > >>>>>>>>>> > > > > >>>>>>>>>> SELECT 'a0eebc99 9c0b4ef8bb6d6bb9bd380a11'::uuid; > > > > >>>>>>>>>> SELECT 'a0eebc999c0b4ef8bb6d6bb9bd380a1 '::uuid; > > > > >>>>>>>>>> SELECT '{a0eebc999c0b4ef8bb6d6bb9bd380a1 }'::uuid; > > > > >>>>>>>>>> SELECT 'a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a1 '::uuid; > > > > >>>>>>>>>> > --------------------------------------------------------------- > > > > >>>>>>>>>> > > > > >>>>>>>>>> These should continue to be rejected in the same way as > the scalar parser. > > > > >>>>>>>>>> Regards, > > > > >>>>>>>>> > > > > >>>>>>>>> Agreed. > > > > >>>>>>>>> > > > > >>>>>>> > > > > >>>>>>> I've attached the updated patch. > > > > >>>>>>> > > > > >>>>>>> Regards, > > > > >>>>>>> > > > > >>>>>>> -- > > > > >>>>>>> Masahiko Sawada > > > > >>>>>>> Amazon Web Services: https://aws.amazon.com > > > > >>>>>> > > > > >>>>>> I noticed a few typos in the comments: > > > > >>>>>> > > > > >>>>>> src/backend/utils/adt/uuid.c > > > > >>>>>> line 56: “scalar implmentation” -> “scalar implementation” > > > > >>>>>> line 109: “swalled” -> “swallowed” > > > > >>>>>> line 110: “kepping” -> “keeping” > > > > >>>>>> line 118: “grammer” -> “grammar” > > > > >>>>>> line 119: “whitespaces” -> “whitespace” > > > > >>>>>> > > > > >>>>>> Could you fix them ? > > > > >>>>> > > > > >>>>> Oops, I fixed them and rechecked other places. > > > > >>>>> > > > > >>>>> I've attached the updated patch. > > > > >>>>> > > > > >>>>> Regards, > > > > >>>>> > > > > >>>>> -- > > > > >>>>> Masahiko Sawada > > > > >>>>> Amazon Web Services: https://aws.amazon.com > > > > >>>> > > > > >>>> The code looks good to me now. I only noticed one small typo > in the > > > > >>>> commit trailer: Reviwed-by should be Reviewed-by. > > > > >>>> > > > > >>>> Otherwise, it looks good. Thank you for fixing these issues. > > > > >>>> > > > > >>> > > > > >>> After spending more time on this patch, I find out two things: > > > > >>> > > > > >>> 1. USE_NO_SIMD doesn't work in uuid.c without including > port/simd.h. > > > > >>> But including port/simd.h seems wrong as it doesn't use any SIMD > > > > >>> support functions. > > > > >>> > > > > >>> 2. hex_decode_safe() is faster than the current UUID parse > > > > >>> (isxdigit()+strtoul() approach) even without SIMD. I've created a > > > > >>> small benchmark test tool (attached as 0002 patch, not intended > to be > > > > >>> pushed into the core), and measures UUID parsing performance of > three > > > > >>> approaches: 'scalar' is the current string_to_uuid() that uses > > > > >>> isxdigit()+strtoul()), 'simd' uses hex_decode_safe() with SIMD, > and > > > > >>> 'nosimd' uses hex_decode_safe() without SIMD, with different > shapes of > > > > >>> UUIDs. Here are results: > > > > >>> > > > > >>> =# select path, shape, n_inputs, best_ms::numeric(10,3) from > > > > >>> uuid_parse_bench(100000, 5); > > > > >>> path | shape | n_inputs | best_ms > > > > >>> --------+------------------+----------+--------- > > > > >>> scalar | canonical | 100000 | 22.661 > > > > >>> simd | canonical | 100000 | 1.400 > > > > >>> nosimd | canonical | 100000 | 1.652 > > > > >>> scalar | bare32 | 100000 | 15.932 > > > > >>> simd | bare32 | 100000 | 0.471 > > > > >>> nosimd | bare32 | 100000 | 1.110 > > > > >>> scalar | braced_canonical | 100000 | 17.330 > > > > >>> simd | braced_canonical | 100000 | 1.088 > > > > >>> nosimd | braced_canonical | 100000 | 1.314 > > > > >>> scalar | braced_bare32 | 100000 | 15.942 > > > > >>> simd | braced_bare32 | 100000 | 0.488 > > > > >>> nosimd | braced_bare32 | 100000 | 1.141 > > > > >>> scalar | dashed4 | 100000 | 16.185 > > > > >>> simd | dashed4 | 100000 | 16.493 > > > > >>> nosimd | dashed4 | 100000 | 16.403 > > > > >>> scalar | invalid_hex | 100000 | 0.199 > > > > >>> simd | invalid_hex | 100000 | 1.150 > > > > >>> nosimd | invalid_hex | 100000 | 0.385 > > > > >>> (18 rows) > > > > >>> > > > > >>> Each of shape means: > > > > >>> - 'canonical': 8x-4x-4x-4x-12x, what uuid_out() emits > > > > >>> - 'bare32': 32 contiguous hex digits > > > > >>> - 'braced_canonical': {8x-4x-4x-4x-12x} > > > > >>> - 'braced_bare32': {32 hex digits} > > > > >>> - 'dashed4': dash after every group of 4 > > > > >>> - 'invalid_hdx': canonical but with a invalid digit > > > > >>> > > > > >>> 'nosimd' is 10x~ faster than 'scalar' in most cases. All paths > are > > > > >>> mostly the same in 'dashed4' and 'invalid_hex' cases because > 'simd' > > > > >>> and 'nosimd' fall back to the 'scalar' case. According to these > > > > >>> results, my conclusion is that we can use hex_decode_safe() for > > > > >>> canonical forms and 32 contiguous hex forms anyway, and let > > > > >>> hex_decode_safe() choose whether to use SIMD. We would win in > either > > > > >>> case. We still use the current scalar approach for uncommon UUID > forms > > > > >>> and error reporting purposes. > > > > >>> > > > > >>> Regards, > > > > >>> > > > > >>> -- > > > > >>> Masahiko Sawada > > > > >>> Amazon Web Services: https://aws.amazon.com > > > > >>> > <v4-0001-Optimize-UUID-parse-using-SIMD.patch><v4-0002-uuid_parse_bench-module.patch> > > > > >> > > > > >> A few comments on v4. > > > > >> > > > > >> 1 - 0001 > > > > >> ``` > > > > >> +static void > > > > >> +string_to_uuid(const char *source, pg_uuid_t *uuid, Node > *escontext) > > > > >> +{ > > > > >> + const char *body = source; > > > > >> + size_t len = strlen(source); > > > > >> ``` > > > > >> > > > > >> I think it would be better to avoid strlen(). The old code > processes at most UUID_LEN (16) byte pairs, so it does not need to scan > arbitrarily far on malformed input. So, maybe we could use something like > strnlen(source, 39) instead. > > > > > > > > > > While strnlen(source, 39) works there, 39 is a magic number and > it's > > > > > tied to the current format check logic. What is the benefit of > using > > > > > strnlen(source, 39) instead? I'm not sure it warrants having the > magic > > > > > number. > > > > > > > > It doesn't have to be exactly 39; 1024 (long enough) would also > work, or perhaps something based on UUID_LEN, such as UUID_LEN * 3. I think > the main point is to avoid unbounded scanning on malformed input. > > > > > > > > The old code did not have this issue because it only examined as > much input as needed based on UUID_LEN. The new fast path starts to use > strlen(), so this would be a new risk introduced by the optimization. > > > > > > I don't think the scan can be really unbounded. string_to_uuid() > > > receives a cstring, so by the time it is called the caller has already > > > walked or copied the whole string to produce it. So unless the > > > unbounded scan can be reached in some path I have overlooked, I'd > > > prefer to keep strlen() here. Happy to change it if you still think it > > > is worth it. > > > > After more thoughts, while I still don't think the scan can be > > unbounded, using strlen() would add an extra scan just to determine we > > use hex_decode_safe(). I'll change it to use strnlen() instead. > > I've updated the patch accordingly. Please review it. > The code looks good to me. Just one tiny thing: you stated that The fast path is deliberately not conditional on SIMD support but the test is still commented as: Test UUID shapes that the parser uses the SIMD path. Maybe it could be changed to: Test UUID shapes handled by the fast path. Thanks, Haibo > > Regards, > > -- > Masahiko Sawada > Amazon Web Services: https://aws.amazon.com >
