Re: Freelist Contention

Not only that, PX slaves do direct reads  anyway, bypassing the buffer cache.

It is possible, though, that the flush
that has to take place before the PX
scan can read back is sufficient to
cause other processes to wait for
write complete waits, and I guess that
you could also get extra rbs header
waits as the flushed and scanned blocks
are rolled back by the PX slaves for
read consistency.

Excessive serial tablescans, on the other hand can easily cause significant buffer busy waits.

Jonathan Lewis

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-----Original Message-----
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Date: 21 August 2001 18:32

|On Tuesday 21 August 2001 08:21, Johnson Poovathummoottil wrote:
|> Bufer busy waits can also be caused by parallel query
|> servers trying to read the same buffer block at the
|> same time.
|
|Just off the top of my head, and without giving it a lot
|of thought, this doesn't sound right.
|
|PQS divvy up the blocks to read, and should not be trying
|to access the same block.
|
|Got any documentation or evidence to back that up?
|
|Jared

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