The original comment was about PQ
slaves reading data blocks - not
PX slaves running parallel update/inserts.
When PX slaves do parallel inserts the
processing is usually split to avoid
contention - e.g. each slaves gets
one partition of a partitioned object;
or each slave gets a new extent above
the HWM of an existing data segment;
so I don't think PX slaves would have
that issue. (which can, of course, be an
issue with 'ordinary' highly concurrent
processes).
Jonathan Lewis
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-----Original Message-----
To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
Date: 23 August 2001 13:42
|Jonathan,
|
|OK, what am I missing? All of the PX sessions have to
|access the segment header in order to get blocks off
|the free lists so can't that result in buffer busy
|waits on the segment header unless it was created with
|more than one free list group?
|
|-- Anita
|
|--- Jonathan Lewis <[EMAIL PROTECTED]>
|wrote:
|>
|> 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.
|>
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