Re: CLUSTER and indisclustered

On Sun, 4 Aug 2002, mark Kirkwood wrote:

> Ok, this change would save you the initial access of the index
> structure itself - but isnt the usual killer for indexes is the
> "thrashing" that happens when the "pointed to" table data is spread
> over a many pages.

Yeah, no kidding on this one. I've reduced queries from 75 seconds
to 0.6 seconds by clustering on the appropriate field.

But after doing some benchmarking of various sorts of random reads
and writes, it occurred to me that there might be optimizations
that could help a lot with this sort of thing. What if, when we've
got an index block with a bunch of entries, instead of doing the
reads in the order of the entries, we do them in the order of the
blocks the entries point to? That would introduce a certain amount
of "sequentialness" to the reads that the OS is not capable of
introducing (since it can't reschedule the reads you're doing, the
way it could reschedule, say, random writes).

cjs
-- 
Curt Sampson  <cjs@cynic.net>   +81 90 7737 2974   http://www.netbsd.org   Don't you know, in this new Dark Age, we're
alllight.  --XTC