Re: FSM search modes

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: "Simon Riggs" <simon(at)2ndQuadrant(dot)com>, "Alvaro Herrera" <alvherre(at)commandprompt(dot)com>, "decibel" <decibel(at)decibel(dot)org>, "Itagaki Takahiro" <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, "pgsql-hackers" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: FSM search modes
Date: 2009-10-01 18:55:18
Message-ID: 1412.1254423318@sss.pgh.pa.us
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"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> So for example we might try resetting the search to the start of the
>> relation with probability 0.01.

> If I understand the heuristic you propose, and my math skill haven't
> eroded too badly from lack of use, every 229 spots considered would
> cause a 90% chance of reset.

Sorry, I wasn't clear. What I was thinking of was that we'd consider
resetting the search position once, upon entry to fsm_search, and then
search normally thereafter. Some experimentation would be needed to
choose the right probability of course. A number like 0.01 might seem
too small to affect the behavior at all, but that's what we thought
about the btree case too. A very light thumb upon the scales may be
sufficient.

regards, tom lane

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