Horton

Re: Change GUC hashtable to use simplehash?

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: John Naylor <johncnaylorls@gmail.com>
Cc: Jeff Davis <pgsql@j-davis.com>, Tom Lane <tgl@sss.pgh.pa.us>, Gurjeet Singh <gurjeet@singh.im>, pgsql-hackers@postgresql.org
Date: 2023-11-22T20:50:30Z
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. Silence warning in older versions of Valgrind

  2. Revert "Speed up tail processing when hashing aligned C strings, take two"

  3. Speed up tail processing when hashing aligned C strings, take two

  4. Teach fasthash_accum to use platform endianness for bytewise loads

  5. Add macro to disable address safety instrumentation

  6. Convert uses of hash_string_pointer to fasthash equivalent

  7. Speed up tail processing when hashing aligned C strings

  8. Add helper functions for dshash tables with string keys.

  9. Fix warnings in cpluspluscheck

  10. Further cosmetic review of hashfn_unstable.h

  11. Simplify initialization of incremental hash state

  12. Add optimized C string hashing

  13. Add inline incremental hash functions for in-memory use

  14. Make all Perl warnings fatal

Hi,

On 2023-11-21 16:42:55 +0700, John Naylor wrote:
> I get a noticeable regression in 0002, though, and I think I see why:
> 
>  guc_name_hash(const char *name)
>  {
> - uint32 result = 0;
> + const unsigned char *bytes = (const unsigned char *)name;
> + int                  blen  = strlen(name);
> 
> The strlen call required for hashbytes() is not free. The lack of
> mixing in the (probably inlined after 0001) previous hash function can
> remedied directly, as in the attached:

I doubt this is a good hashfunction. For short strings, sure, but after
that...  I don't think it makes sense to reduce the internal state of a hash
function to something this small.

Greetings,

Andres Freund