Nitin,
I think I'd look at a couple of other figures before trying to fiddle with
undocumented parameters.
What does the wait event histogram say about change tracking writes and reads ?
Any clues that there's an I/O problem there ?
How about checking the size and free space in the large pool - changing the
allocation size may make no difference if the large pool can't supply it. Maybe
setting a larger large_pool_size would be sufficient.
It's a long time since I looked at BCT, but maybe your data files are growing
and this is putting some odd pressure on your change tracking file that's
causing delays with writes to the file.
Regards
Jonathan Lewis
________________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> on behalf
of Nitin Saxena <ntnsxn7@xxxxxxxxx>
Sent: 13 March 2018 00:48
To: ORACLE-L
Subject: block change tracking buffer space !
Hello Everyone,
I am facing lot of concurrency wait events due to "block change tracking buffer
space" when rman L0 backup is run. I see that database gets overwhelmed with
concurrency due to less space for CTWR buffer as shown in event. I see
following problem area . Any recommendations if we should bump
"_bct_public_dba_buffer_size" to higher value ?
NAME VALUE
DESCRIPTION
--------------------------------------------- ------------------------------
-------------------------------------------------------
_bct_public_dba_buffer_size 0
total size of all public change tracking dba buffers,
in
bytes
NAME VALUE
DESCRIPTION
--------------------------------------------- ------------------------------
-------------------------------------------------------
_bct_buffer_allocation_max 104857600
maximum size of all change tracking buffer allocations,
in
bytes
SQL> select dba_buffer_count_public*dba_entry_count_public*dba_entry_size from
X$KRCSTAT;
DBA_BUFFER_COUNT_PUBLIC*DBA_ENTRY_COUNT_PUBLIC*DBA_ENTRY_SIZE
-------------------------------------------------------------
25276400
SQL> SELECT * FROM v$sgastat WHERE name like 'CTWR%';
POOL NAME BYTES
------------ -------------------------- ----------
large pool CTWR dba buffer 11386880
snippet from ash and dash is as follows:
%This SECONDS WAIT_CHAIN
------ ----------
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
12% 14650 -> 1vyayutd1117p:buffer busy waits -> 1vyayutd1117p:block
change tracking buffer space
--
Cheers
Nitin
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