From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: Thomas Munro <thomas.munro@enterprisedb.com>,
        pgsql-hackers@lists.postgresql.org
Subject: Re: Ensuring hash tuples are properly maxaligned
In-reply-to: <20180103013300.cf4jermw5ksygm7l@alap3.anarazel.de>
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Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Tue, 02 Jan 2018 17:33:00 -0800"
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Date: Tue, 02 Jan 2018 20:40:50 -0500
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Andres Freund <andres@anarazel.de> writes:
> On 2018-01-03 14:29:15 +1300, Thomas Munro wrote:
>> On Wed, Jan 3, 2018 at 2:20 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> Andres Freund <andres@anarazel.de> writes:
>>> But note that dsa_pointer can be wider than a regular pointer on
>>> platforms without atomics support.

>>> Hm.  I did not get that impression from the comments in dsa.h,
>>> but if it's true then this approach won't work --- and indeed the
>>> hash code would be actively broken in such a case, so it's a problem
>>> we must fix.

>> Maybe Andres is thinking of dsa_pointer_atomic?  dsa_pointer is
>> normally the size of a pointer (well, really, the size of size_t),
>> though it could be *narrower* if you don't have atomics or ask for it
>> with USE_SMALL_DSA_POINTER

> Yep, I was.

OK, then there's not a live bug, but I'm a bit tempted to get rid of
the data[] member anyway.  It's not clear to me now that keeping it
results in net cleaner code.  Thoughts?

			regards, tom lane