Re: Re: [COMMITTERS] pgsql: Adjust OLDSERXID_MAX_PAGE based on BLCKSZ.

Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> On 08.07.2011 15:22, Kevin Grittner wrote:
>> Heikki Linnakangas wrote:
>>> I'm getting a bunch of warnings on Windows related to this:
>>> .\src\backend\storage\lmgr\predicate.c(768): warning C4307: '+' :
>>> integral constant overflow

>> The part of the expression which is probably causing this:
>>
>> (MaxTransactionId + 1) / OLDSERXID_ENTRIESPERPAGE - 1
>>
>> Which I fear may not be getting into overflow which will not do the
>> right thing even where there is no warning. :-(
>>
>> Would it be safe to assume that integer division would do the right
>> thing if we drop both of the "off by one" adjustments and use?:
>>
>> MaxTransactionId / OLDSERXID_ENTRIESPERPAGE

> Hmm, that seems more correct to me anyway. We are trying to calculate
> which page xid MaxTransactionId would be stored on, if the SLRU didn't
> have a size limit. You calculate that with simply MaxTransactionId /
> OLDSERXID_ENTRIESPERPAGE.

So, what are the consequences if a compiler allows the expression to
overflow to zero? Does this mean that beta3 is dangerously broken?

regards, tom lane