Re: "gc cr multi block request" and "Current Blocks Received"
- From: Riyaj Shamsudeen <riyaj.shamsudeen@xxxxxxxxx>
- To: kamusis@xxxxxxxxx
- Date: Sat, 20 Nov 2010 13:38:25 -0600
Hello Kamusis,
Event 'gc buffer busy' waits simply means that the blocks are already
involved in some sort of Global cache operation.
Event 'gc cr multi block request' is for Full table scan or full index
scan operations (similar to db file scattered read). Segment statistics
lists only top 5 segments and if the application reads lots of different
segments (such as partition scans or scans on different segments, that might
not show up in AWR report). You might want to query gv$segment_statistics
directly.
To answer your question, no, if the session requests a CR block, it will
get CR block and the 'gc cr blocks received' will be incremented. Only
exception (I can think of) , in which, sessions might need to request
Current block is that, if the 'lightworks rule' kicked in and the sessions
has to apply much undo blocks from different instance to fabricate specific
version of the block.
Cheers
Riyaj Shamsudeen
Principal DBA,
Ora!nternals - http://www.orainternals.com - Specialists in Performance,
Recovery and EBS11i
Blog: http://orainternals.wordpress.com
OakTable member http://www.oaktable.com
Co-author: "Expert Oracle practices: Oracle Database Administration from the
Oak Table" http://www.apress.com/book/view/9781430226680
On Fri, Nov 19, 2010 at 5:21 PM, Leyi Zhang (Kamus) <kamusis@xxxxxxxxx>wrote:
> Hi, experts:
>
> We have a RAC system, in AWR report "gc buffer busy" is top 1 wait (31
> Percent Total DB Time), and "gc cr multi block request" is the 2nd (21
> Percent Total DB Time)
>
> But in AWR report - "Segment Statistics" section ,we can only find
> there are lots of "Current Blocks Received", not so much "CR Blocks
> Received".
>
> So my question is: Is it possible If a session waiting on "gc cr multi
> block request" and then it received a "Current Block"?
>
> --
> Kamus <kamusis@xxxxxxxxx>
>
> Visit my blog for more : http://www.dbform.com
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