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

Oracle Data Guard

Tuning the Data Guard Log Apply Services

The log apply service is the slowest phase in the process of data synchronization in a Data Guard environment. If the log transfer service is well tuned, the DBA should divert attention to tuning the log apply service. On a logical database, the log apply service uses the SQL apply method. On a physical standby database, it uses a block-per-block media recovery.

For this reason, the log apply service on a physical Oracle instance is more efficient than on the logical standby database. In this section, the collection of data needed for performance tuning of the log apply service will be presented. Interpreting this information and applying corrective measures will also be discussed.

Gathering Log Apply Service Related Statistics

Performance data gathering on physical and logical standby databases will be covered in this section. For this chapter, the information will start with the physical standby database.

Physical Standby Database

As mentioned earlier, the log apply services on a physical Oracle instance rarely cause performance issues. However, run some periodic checks to ensure that it is not falling behind. Querying the dynamic performance table v$managed_standby will reveal if the log apply is not coping with the amount of redo generated by the primary database.

The script, MngStandby.sql, from the code depot can be used for this purpose. Execute this script on the physical standby database:

Gathering Log Apply Service Related Statistics
Physical Standby Database

            MngStandby.sql

-- *************************************************
-- Copyright © 2015 by Rampant TechPress
-- *************************************************
 
-- Script to monitor the log apply service performance on
-- physical standby database.
 
Set Linesize 90
Column Process Format a7
Column Status Format a12
Column Sequence# Format 9999999999
Column Block# Format 99999999
Column Blocks Format 99999999
 
Select
   Process,
   Status,
   Sequence#,
   Block#,
   Blocks
From
   See code depot for full scripts
   V$MANAGED_STANDBY;