Re: Question about explain of index scan - Mailing list pgsql-hackers

From Tom Lane
Subject Re: Question about explain of index scan
Date
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In response to Re: Question about explain of index scan  (Alvaro Herrera <[email protected]>)
List pgsql-hackers
Alvaro Herrera <[email protected]> writes:
> On Sun, Sep 04, 2005 at 06:21:51PM -0400, Tom Lane wrote:
>> XID comparison works OK as long as you make sure that all the XIDs
>> extant in the system at any one time are within +/- 2 billion of each
>> other, and so transitivity does hold within that subset.  The problem
>> with a btree is that upper-level tree nodes are likely to contain page
>> boundary keys copied from data that vanished some time ago from the
>> underlying table.

> So there would be no problem if a REINDEX was forced every two billion
> transactions, right?  (A bit less, I think.)

That seems a bit brute-force, but it'd probably work.  (IIRC the
convention we use for vacuuming is to force some activity every 1
billion transactions, because waiting 2 billion leaves no safety
margin.)
        regards, tom lane


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