Re: BUG #8673: Could not open file "pg_multixact/members/xxxx" on slave during hot_standby

Tom Lane wrote:
> Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> > After some simplification I think it should be clearer. Thanks Andres
> > for commenting offlist.
>
> I find this not only unreadable but a bit scary:
>
> ! if (offset + MAX_MEMBERS_IN_LAST_MEMBERS_PAGE < offset)
>
> I'm worried whether some compilers might not decide that that's a
> can't-happen situation, and optimize the test away entirely. I think
> Andres' proposal is probably safer (though it needs comments).

Well, somebody would have to work it out fully and test it -- I can't
spend more time on this issue. If somebody is interested in doing that,
I used this little program and make sure that it "zeroes" all pages, for
various block sizes, initial offsets and "step sizes" (#members in each
multi) -- I was able to reproduce Serge's issues with the original
coding, and then watch issues fly by as I tried several approaches until
I settled on the patch as submitted.

--
Álvaro Herrera http://www.2ndQuadrant.com/
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