Re: "gc cr multi block request" and "Current Blocks Received"

Interesting.

I try to reproduce it in my Oracle 10.2.0.4 2-nodes RAC, but have no luck.

In rac2 intance, I insert some new rows into table T, and try to remaster it manually:

SQL> insert into kamus.t select * from dba_objects;

10300 rows created.

SQL> select count(*) from kamus.t;

  COUNT(*)

    348792

SQL> select object_id,data_object_id from dba_objects where object_name='T';

 OBJECT_ID DATA_OBJECT_ID
---------- --------------

     23143 23143

SQL> oradebug lkdebug -m 23143
Statement processed.
SQL> In rac1 instance:
SQL> select name,value from v$sysstat where NAME in ('gc cr blocks received','gc current blocks received');

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
gc cr blocks received                                                  2317
gc current blocks received                                             6204

SQL> /

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
gc cr blocks received                                                  2317
gc current blocks received                                             6204

SQL> select count(*) from kamus.t;

  COUNT(*)

    338492

SQL> select name,value from v$sysstat where NAME in ('gc cr blocks received','gc current blocks received');

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
gc cr blocks received                                                  2603
gc current blocks received                                             6205

Only got 1 block "gc current blocks received" and all others are "gc cr blocks received".

--
Kamus <kamusis_at_gmail.com>

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On Sun, Nov 21, 2010 at 8:03 AM, K Gopalakrishnan <kaygopal_at_gmail.com> wrote:


> Kamus,

> Depending on the state of the block and mode, you might get a cr block or

> current block.�Here is the possible operations for your gc cr request. I

> have dealt these issues little bit �in my upcoming 11g RAC book, however you

> might have to wait for few months to get a copy in your hand. So to answer

> your question here is the possible answer.

> If 'gc cr request' is made from your instance

> If the block is not cached elsewhere,

> You get the CR grant, and wait on 2-3 way messages.

> If the block is held in X mode in another in another instance

> Holder constructs CR copy and you get the block.

> <gc cr block received>

> If the block held in S mode in another instance,

> And if the holder=master, you get the current block.

> <gc current blocks received>

> However please keep in mind undo block (header/data) transfers are always

> current blocks, though it increments the 'gc cr blocks received' stats.

> -Gopal

>

>

> On Fri, Nov 19, 2010 at 5:21 PM, Leyi Zhang (Kamus) <kamusis_at_gmail.com>

> 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"?

>>

>> --

>>

>

>

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