Обсуждение: Clarification Regarding Vacuum and template1

Hi :


Saw this post on BUGS mailing list :

"Olleg Samoylov" <olleg_s ( at ) mail ( dot ) ru> writes:
>> Opps, template1 must not be vacuumed.

>Says who?

>If we didn't vacuum template1 then it would be subject to
>XID wraparound
>problems, unless it had never been modified, which is
>something vacuumdb
>can't count on.

> regards, tom lane

  Under normal circumstances, there's no need to vacuum
template1 right? Its quite difficult to imagine XID
wraparound problems occuring in template1. I can't think
how can 4 billion transactions occur in template1 if
template1 is just used as a template in creating a new
database.

  Am I missing something here?

Thank you very much,

ludwig lim

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Ludwig Isaac Lim <ludz_lim@yahoo.com> writes:
>   Under normal circumstances, there's no need to vacuum
> template1 right?

Only if it hasn't been modified.

> Its quite difficult to imagine XID
> wraparound problems occuring in template1. I can't think
> how can 4 billion transactions occur in template1 if
> template1 is just used as a template in creating a new
> database.

>   Am I missing something here?

Yes: the wraparound limit is for transactions cluster-wide, not per
database.  If you make 1 change in template1 and then 2 billion
changes in some other databases, template1 is broken unless it's
been vacuumed meanwhile.

            regards, tom lane

>
> Yes: the wraparound limit is for transactions
> cluster-wide, not per
> database.  If you make 1 change in template1 and then 2
> billion
> changes in some other databases, template1 is broken
> unless it's
> been vacuumed meanwhile.
>
>             regards, tom lane
>

   So in practice,  should  one vacuum template1  when
vacuuming other database (Assuming one doesn't use vaccumdb
script when vacuuming database)?

   Will this problem occur if I vacuum all database except
template1?

   Thanks for the previous quick response.

   Thank you once again.

ludwig lim

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>    So in practice,  should  one vacuum template1  when
> vacuuming other database (Assuming one doesn't use vaccumdb
> script when vacuuming database)?

In practice, it shouldn't be a big deal to vacuum template1 once in a
while, because, since it shouldn't have much data other than
pg_catalog tables in it, it shouldn't take long to vacuum it.

If you vacuum it once a day or once a week or such, the 15 seconds
won't take much out of the life of the disk drives...
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