| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Mark Dilger <mark(dot)dilger(at)enterprisedb(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru>, Stephen Frost <sfrost(at)snowman(dot)net>, Michael Paquier <michael(at)paquier(dot)xyz>, Amul Sul <sulamul(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: new heapcheck contrib module |
| Date: | 2020-10-22 22:45:15 |
| Message-ID: | 95051.1603406715@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Mark Dilger <mark(dot)dilger(at)enterprisedb(dot)com> writes:
>> On Oct 22, 2020, at 2:06 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Oh, wait a second. ItemIdData has the flag bits in the middle:
>> meaning that for that particular bit pattern, one endianness
>> is going to see the flags as 01 (LP_NORMAL) and the other as 10
>> (LP_REDIRECT).
> Well, the issue is that on big-endian machines it is not reporting any
> corruption at all. Are you sure the difference will be LP_NORMAL vs
> LP_REDIRECT?
[ thinks a bit harder... ] Probably not. The byte/bit string looks
the same either way, given that it's four repetitions of the same
byte value. But which field is which will differ: we have either
oooooooooooooooFFlllllllllllllll
01110111011101110111011101110111
or
lllllllllllllllFFooooooooooooooo
01110111011101110111011101110111
So now I think this is a REDIRECT on either architecture, but the
offset and length fields have different values, causing the redirect
pointer to point to different places. Maybe it happens to point
at a DEAD tuple in the big-endian case.
regards, tom lane
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