Data Guard Log Apply Statistics Oracle Database Tips by Donald BurlesonDecember 9, 2015

Oracle Data Guard- Performance Tuning of Data Guard Configuration

Gathering Log Apply Service Related Statistics
Physical Standby Database

The following is a sample output from the script:

PROCESS STATUS         SEQUENCE#    BLOCK#    BLOCKS
------- ------------ ----------- --------- ---------
ARCH    CONNECTED              0         0         0
ARCH    CONNECTED              0         0         0
RFS     RECEIVING           1965      2046      2046
RFS     ATTACHING           1964      2046      2046
MRP0    WAIT_FOR_LOG        1948      2044      2046

The SEQUENCE# column indicates the archived log file sequence number being processed. A significant difference between the SEQUENCE# of RFS and MRP0 shows a poor performance of the log apply service.

Logical Standby Database Log Apply Services

In order to find the overall progress of the log apply service on a logical standby database, the dba_logstdby_progress view can be queried. The view provides read and applied SCN. The script named log_progress.sql, from the code depot, can be executed on a logical Oracle instance in order to find the overall progress of the log apply service. This should be the starting point in the diagnosis of performance issues with SQL apply operation. A sample output from the log_progress.sql is shown below:

APPLIED_SCN      READ_SCN      NEWEST_SCN
------------- ------------- ---------------
      2187154       1987779         2187417

If the APPLIED_SCN and NEWEST_SCN are the same, the SQL apply operation has applied all the available transactions. In cases where these two values are not equal, further investigation into the level of individual processes involved in the SQL apply operation is required.

Querying the dynamic performance v$logstdby on a logical Oracle instance will provide the performance of individual processes involved in the SQL apply operation. The script, sql_apply_progress.sql, from the code depot can be used to gather data from v$logstdby.

            sql_apply_progress.sql

-- *************************************************
-- Copyright © 2015 by Rampant TechPress
-- *************************************************

-- Script to find out the progress of individual process
-- involved in SQL Apply operation
column Type Format a12
Column Status Format a40 Trunc
Column High_Scn Format 999999999
Select
   Type,
   Status,
   High_Scn
   See code depot for full scripts
From
   V$LOGSTDBY;

A sample output from the script is shown below:

TYPE         STATUS                                     HIGH_SCN
------------ ---------------------------------------- ----------
COORDINATOR  ORA-16116: no work available
READER       ORA-16127: stalled waiting for additiona
BUILDER      ORA-16127: stalled waiting for additiona    2187196
PREPARER     ORA-16116: no work available                2187196
ANALYZER     ORA-16117: processing                       2187196
APPLIER      ORA-16117: processing                       2187156