| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
| Cc: | Hannu Krosing <hannu(at)skype(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Question about explain of index scan |
| Date: | 2005-09-04 23:29:10 |
| Message-ID: | 9520.1125876550@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> 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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