On Wed, 7 Aug 2002, Curt Sampson wrote:
> 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).
This sounds more or less like the method employed by Firebird as described
by Ann Douglas to Tom at OSCON (correct me if I get this wrong).
Basically, firebird populates a bitmap with entries the scan is interested
in. The bitmap is populated in page order so that all entries on the same
heap page can be fetched at once.
This is totally different to the way postgres does things and would
require significant modification to the index access methods.
Gavin