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Sizing the Data Guard SQL Apply LCR cache

Oracle Database Tips by Donald BurlesonConsulting

May 7, 2015

Question:  I am getting g the ORA-16243 error when doing logical standby replication in Data Guard:

APPLIER 16116 ORA-16116: no work available
BUILDER 16243 ORA-16243: paging out 2816 bytes of memory to disk
COORDINATOR 16116 ORA-16116: no work available


How can we identify the table/SQL to skip & instantiate the table rows later?

Answer:  That is NOT supported, since holding-back a table might cause logical corruption (e.g. orphan rows) in constraints.  The docs note that the ORA-16243 error simply notes that it has paged out to disk:

ORA-16243: paging out string bytes of memory to disk

Cause: Builder process is paging out memory to free up space in Logical Change Record (LCR) cache.

Action: No action necessary, this informational statement is provided to record the event for diagnostic purposes.

Your root cause solution is to tune the logical standby to get the transactions applied faster.

The LCRs for Data Guard SQL Apply are staged in the shared pool of the system global area (SGA), in a heap that is known as the "Logical Change Record cache" or LCR cache.  The ORA-16243 error happens when you don't allocate enough RAM to the SQL Apply process.

To increase the SQL Apply LCR cache size, follow these steps:

1 - Start by increasing shared_pool_size (or sga_max_size if using AMM)

2 - Increase the size of the LCR cache memory.  This will double your existing LCR cache size:

execute dbms_logstdby.apply_set('MAX_SGA',4800);

3 - Look at parallelization of the LCR.  To allocate 30 parallel query servers for logical standby log apply services, enter the following statement:

execute dbms_logstdby.apply_set('max_servers', 30);

For complete tuning details for Oracle Data Guard, see the book Oracle Data Guard.
 
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