| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Pavel Borisov <pashkin(dot)elfe(at)gmail(dot)com> |
| Cc: | Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, Postgres hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: [PATCH] Improve treatment of page special and page header alignment during page init. |
| Date: | 2021-04-07 15:38:15 |
| Message-ID: | 1593715.1617809895@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Pavel Borisov <pashkin(dot)elfe(at)gmail(dot)com> writes:
>> How can we say that in PageInit the SizeOfPageHeaderData is expected
>> to be max aligned? Am I missing something? There are lots of other
>> places where SizeOfPageHeaderData is used, not
>> MAXALIGN(SizeOfPageHeaderData).
> Its maxalign is ensured by its size of 24bytes (which is maxalign'ed). I
> think if we change this to not-maxalign'ed value bad things can happen. So
> I've added assert checking for this value. I think it is similar situation
> for both page header and page special, I wonder why they've been treated
> differently in PageInit.
No, that's wrong. What follows the page header is the line pointer
array, which is only int-aligned. We need to maxalign the special
space because tuples are stored working backwards from that, and
we want maxalignment for tuples.
regards, tom lane
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