| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Hash twice |
| Date: | 2013-01-14 19:12:24 |
| Message-ID: | CA+TgmoYB0L8oDLopPC81s63NGOvqzyaY4o_kRH09_wgEpJnWUw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sat, Jan 12, 2013 at 11:39 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> Lock code says it calculates "hash value once and then pass around as needed".
>
> But it actually calculates it twice for new locks.
>
> Trivial patch attached to make it follow the comments in
> LockTagHashCode and save a few cycles.
Hmm. This is a nice idea, but it doesn't look right to me, because
you're searching LockMethodLocalHash with a hash code intended to be
used in LockMethodLockHash, and the two hashing schemes are not
compatible, because the former is hashing a LOCALLOCKTAG, and the
latter is hashing a LOCKTAG, and both are just using tag_hash.
On the flip side if I'm wrong and the hashing schemes are compatible,
there are other places in the file where the same trick could be
employed.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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