Horton

Re: Change GUC hashtable to use simplehash?

John Naylor <johncnaylorls@gmail.com>

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From: John Naylor <johncnaylorls@gmail.com>
To: Jeff Davis <pgsql@j-davis.com>
Cc: Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>, Gurjeet Singh <gurjeet@singh.im>, pgsql-hackers@postgresql.org
Date: 2023-11-22T07:09:12Z
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

On Wed, Nov 22, 2023 at 12:00 AM Jeff Davis <pgsql@j-davis.com> wrote:
>
> On Tue, 2023-11-21 at 16:42 +0700, John Naylor wrote:
> > The strlen call required for hashbytes() is not free.
>
> Should we have a hash_string() that's like hash_bytes() but checks for
> the NUL terminator itself?
>
> That wouldn't be inlinable, but it would save on the strlen() call. It
> might benefit some other callers?

We do have string_hash(), which...calls strlen. :-)

Thinking some more, I'm not quite comfortable with the number of
places in these patches that have to know about the pre-downcased
strings, or whether we need that in the first place. If lower case is
common enough to optimize for, it seems the equality function can just
check strict equality on the char and only on mismatch try downcasing
before returning false. Doing our own function would allow the
compiler to inline it, or at least keep it on the same page. Further,
the old hash function shouldn't need to branch to do the same
downcasing, since hashing is lossy anyway. In the keyword hashes, we
just do "*ch |= 0x20", which downcases letters and turns undercores to
DEL. I can take a stab at that later.