Monitoring the Data Guard Log apply service Oracle Database Tips by Donald BurlesonDecember 9, 2015

Monitoring Data Guard Log Apply Services

The v$logstdby and v$logstdby_stats views provide comprehensive data about the various processes involved in the SQL Apply operations. As mentioned earlier in the "Data Guard Architecture" chapter, the SQL Apply operation is facilitated by LogMiner technology.

The v$logstdby view can be queried to find the state of the individual process of LogMiner. The following simple query on v$logstdby will give sufficient information needed to analyze any problem with the log apply service:

Oracle Data Guard

Monitoring Log Apply Services

Select
   PID,
   TYPE,
   STATUS
From
   V$LOGSTDBY
Order by
   HIGH_SCN;

The following is a sample output, from the above query showing the status of the log apply service:

PID    TYPE         STATUS
------ --------     -------------------------------------
1479   ANALYZER     ORA-16116: no work available
1475   BUILDER      ORA-16127: stalled waiting for additional
                    transactions to be applied
1477   PREPARER     ORA-16116: no work available
1471   COORDINATOR  ORA-16116: no work available
1473   READER       ORA-16127: stalled waiting for additional
                    transactions to be applied
1481   APPLIER      ORA-16116: no work available

Monitoring Log Apply Services

The v$logstdby_stats view contains the performance statistics on the log apply service. The records from this view will be cleared when the log apply service is not running. The following query can be used for performance monitoring purposes:

Select
   NAME,
   VALUE
From
   V$LOGSTDBY_STATS;

The output from the v$logstdby_stats view is as follows:

NAME                                   VALUE
-----                              ---------
number of preparers                  1
number of appliers                   1
maximum SGA for LCR cache            2
parallel servers in use              5
maximum events recorded            100
transaction consistency            FULL
record skip errors                   Y
record skip DDL                      Y
record applied DDL                   Y

NAME                                   VALUE
-----                              ---------
coordinator state                                          APPLYING
transactions ready                                                         2
transactions applied                                                      2
coordinator uptime                                                       4
preparer memory alloc waits                                         2
builder memory alloc waits                                      2346
attempts to handle low memory                               2346
successful low memory recovery                                    1
pageout avoided                                                           0
pageout avoided by rollback                                         0
pageouts                                                                       0
memory low watermark reached                                   0
recovery checkpoints not taken                                     0
recovery checkpoints taken                                           0
available work units                                                  155
prepared work units                                                      0
committed txns ready                                                    0
un-committed txns ready                                               0
committed txns being applied                                         0
un-committed txns being applied                                    0

Monitoring Log Apply Services

Column Thread      format 99
Column Status_Code format a10

Select
   l.FILE_NAME Archive_Log_Name,
   l.THREAD# Thread,
   e.STATUS_CODE Status_Code
From
   DBA_LOGSTDBY_LOG l,
   DBA_LOGSTDBY_EVENTS e
SEE CODE DEPOT FOR FULL SCRIPT