| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>,Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>,"pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>,Jeff Davis <pgsql(at)j-davis(dot)com>,Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>,amul sul <sulamul(at)gmail(dot)com> |
| Subject: | Re: Hash Functions |
| Date: | 2017-05-14 03:47:39 |
| Message-ID: | 52778957-B778-415F-AEC1-CFD9F4842BCB@anarazel.de |
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| Lists: | pgsql-hackers |
On May 13, 2017 8:44:22 PM PDT, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>On Sat, May 13, 2017 at 7:08 PM, Andres Freund <andres(at)anarazel(dot)de>
>wrote:
>> I seriously doubt that's true. A lot of more complex types have
>> internal alignment padding and such.
>
>True, but I believe we require those padding bytes to be zero. If we
>didn't, then hstore_hash would be broken already.
It'll be differently sized on different platforms. So everyone will have to write hash functions that look at each member individually, rather than hashing the entire struct at once. And for each member you'll have to use a type specific hash function...
Andres
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