Re: XIDs and big boxes again ...

Tom Lane wrote:
> Gregory Stark <stark@enterprisedb.com> writes:
>   
>> ... Keep in mind you're proposing to make everything run 3% slower instead of
>> using that 3% i/o bandwidth headroom to run vacuum outside the critical path.
>>     
>
> I think that's actually understating the problem.  Assuming this is a
> 64-bit machine (which it had better be, if you want XID to be 64 bits...)
> then the effective increase in tuple header size is not just 12 bytes
> but 16 bytes, due to alignment padding.  Greg's 3% overhead number is
> only on-target if your average row width is presently about 530 bytes.
> It could easily be a whole lot less than that, and the overhead
> proportionally higher.
>
>             regards, tom lane
>   


overhead is not an issue here - if i lose 10 or 15% i am totally fine as 
long as i can reduce vacuum overhead to an absolute minimum.
overhead will vary with row sizes anyway - this is not the point.

the point is that you don't want to potentially vacuum a table when only 
a handful of records has been changed.
   many thanks,
      hans

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