Re: How to avoid transaction ID wrap

Tom Lane wrote:
> Zdenek Kotala <Zdenek.Kotala@Sun.COM> writes:
>> Koichi Suzuki wrote:
>>> I've once proposed a patch for 64bit transaction ID, but this causes 
>>> some overhead to each tuple (XMIN and XMAX).
> 
>> Did you check performance on 32-bit or 64-bit systems and 64-bit binary 
>> version of PGSQL? I think that today is not problem to have 64-bit 
>> architecture and 64-bit ID should increase scalability of Postgres.

I checked the performance on 64-bit system and 64bit binary.

> 
> The percentage increase in I/O demand is the main reason the patch was
> rejected, not so much the arithmetic.

That's right.  I've also ovserved I/O demand increase.   I remember we
have to pay three to five percent performance decrease in pgbench.  So I
don't think we should apply this patch without further justification.
I'm looking for other reasons for larger transaction ID.


> 
>             regards, tom lane
> 
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-- 
Koichi Suzuki