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Re: Block B-Tree concept

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Block B-Tree concept
Date: 2006-09-26 12:51:10
Message-ID: 23964.1159275070@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> Tom Lane wrote:
>> VACUUM?
>> 
> There's a few options that I've thought of this far:

> 1. Whenever a tuple is found dead on page X, vacuum of the index will 
> have to go to that page again to see if there's any matching tuples left.

Anything that involves having VACUUM re-evaluate index expressions is a
nonstarter ... or have you already forgotten the optimizations we put
into 8.2 that assume, eg, no sub-transactions within a VACUUM?

> 2. Have a reference counter on index tuple that's increased on insert 
> and decreased by vacuum.

The "increase on insert" part I understand, the "decrease by vacuum"
part seems to have the same problem as #1.  How do you tell which index
entries should be changed?

> 3. Do nothing. Let index scans mark the index tuple as dead when it's 
> convenient. There's no correctness problem with just leaving dead index 
> tuples there, because you have to check the index quals on each heap 
> tuple anyway when you scan.

And we're back to routine REINDEX I guess :-(.  This doesn't seem like a
satisfactory answer.

			regards, tom lane

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