pctused bs

From: Greg Moore <sqlgreg_at_pacbell.net>
Date: Wed, 06 Jun 2001 22:54:05 -0700
Message-ID: <F001.0031FA9E.20010606230022@fatcity.com>

The general theory about increasing PCTUSED is that blocks will be fuller, but they may go on and off the freelist more often and that will hurt DML performance.

But in reality what is the overhead of this? Isn't the need to bring more blocks in and out of the data buffer greater than the overhead of taking such a block on and off the freelist?

How the heck does a person measure what the overhead is of taking a block on and off the freelist? Furthermore, even if you have a measure, how do you compare the disadvantage from fuller blocks going on and off a freelist against the advantage of fuller blocks making full table scans faster?

I see all this stuff in books, but it's just a lot of general statements that amount to so much garbage. It can sound fancy to talk about PCTUSED, and if you can do it in a book you can pose as an expert and fool most hiring managers into thinking you're an expert, but unless you can actually measure the gains and the losses from changing this parameter, what good is any of this talk?

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Author: Greg Moore
  INET: sqlgreg_at_pacbell.net

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