Overhead to consistent gets?
- From: Jonathan Gennick <jonathan@xxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Wed, 11 Jan 2006 22:16:34 -0500
A reader just asked me an interesting question, to which I can only
answer "I don't know". But I'd sure like to know, so in the interests
of gaining enlightnment here's the question:
Is there likely to be a performance difference between the following
two situations:
a) Your query reads 1000 rows packed into 10 blocks. All blocks
are already in the buffer cache (no physical reads). No other
transaction has updated the blocks.
b) Your query reads the same 1000 rows, but this time they are
scattered over, say, 50 blocks. Again, all blocks are in cache. No
other transaction has updated the blocks.
Case b results in more consistent gets. But the same number of rows
are returned in either case. This question seems to boil down to
"what's the overhead to a consistent get?"
And, my own question that I'll is: do things change if another
transaction has updated the blocks since your transaction began?
Best regards,
Jonathan Gennick --- Brighten the corner where you are
http://Gennick.com * 906.387.1698 * mailto:jonathan@xxxxxxxxxxx
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