Re: buffer busy waits and v$filestat

From: Prem Khanna J <jprem_at_kssnet.co.jp>
Date: Tue, 29 Jul 2003 18:34:23 -0800
Message-ID: <F001.005C7B93.20030729183423@fatcity.com>

Gogala,

<quote>

	RMAN is writing the block. That's right, RMAN locks (pins) blocks in
	memory, otherwise it couldn't ensure consistent backup. That is the reason
	why RMAN doesn't need "alter tablespace begin backup" command.

</quote>

I have read that RMAN has the advantage of not generating excessive redo which "alter tablespace begin backup" does.

When RMAN locks a data block while backup and suppose if some data is to be written to the same data block,what happens now ?

1.where will the data be until RMAN releases the lock ? 2.will this be a wait event.if so,how can it be identified ?

Sorry,if i sound silly.
i am going thro' the RMAN book by Robert Freeman and so curious to know ?!

Regards,
Jp.

30-07-2003 06:49:23, Mladen Gogala <mgogala_at_adelphia.net> wrote:
>Buffer busy wait has a different correlation with v$filestat and I/O. Buffer
>busy wait simply means that the buffer you're waiting for is pinned by
>somebody else.
>There are 3 classic situations:
>1) DBWR hasn't finished writing to the disk yet.
>2) Block is locked by another node (OPS, RAC).
>3) RMAN is writing the block. That's right, RMAN locks (pins) blocks in
> memory, otherwise it couldn't ensure consistent backup. That is the reason
> why RMAN doesn't need "alter tablespace begin backup" command.
>To make the long story short, there is a note on metalink (Note:155971.1) with
>an appropriate title: Resolving Intense and "Random" Buffer Busy Wait
>Performance Problems. Buffer busy waits are usually a consequence of I/O
>subsystem not being to provide enough throughput to the database. What can you
>do with v$filestat? You can find where are your hot spots and fix the problem.

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Author: Prem Khanna J
  INET: jprem_at_kssnet.co.jp

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Received on Tue Jul 29 2003 - 21:34:23 CDT