block change tracking buffer space !

From: Nitin Saxena <ntnsxn7_at_gmail.com>
Date: Mon, 12 Mar 2018 17:48:08 -0700
Message-ID: <CAM+YwA_usUdgs2QUM_b4xHweqJUX4ugOUWWYdovaPUpr8mcHpg_at_mail.gmail.com>

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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Received on Tue Mar 13 2018 - 01:48:08 CET