Tuning the Database - Expert Oracle RAC Performance Diagnostics and Tuning - page 308

In addition to the INMEMORY attribute, two other attributes that could be helpful in the activity are PRIORITY
and DISTRIBUTE . PRIORITY indicates the priority of populating the in-memory area with data from the tables that
have the attribute INMEMORY , and DISTRIBUTE indicates the distribution of data in a RAC environment, should all
the data be populated into all the instances in-memory area or should the data be split and distributed to the
respective instances.
To better understand the behavior and utilization of the data in the in-memory area, let's sample the process via
a workshop.

Workshop
In this workshop, let's discuss the creation of the in-memory area, its access, and how to monitor its functioning and
memory utilization.

Step 1
The first step in a process of configuring the in-memory functionality is to identify tables that are good candidates
for analytical operations and can benefit from the columnar format. Alter the table metadata and add the INMEMORY
attributes.

ALTER TABLE STOCK INMEMORY PRIORITY LOW;
ALTER TABLE DISTRICT INMEMORY PRIORITY LOW;

Step 2
Allocate the fixed area in the SGA that will be used to store the data in a columnar format. With the PRIORITY LOW
option, data is loaded after instance startup, but after all preliminary instance level startup functions including
instance recovery are complete. The fixed area of the SGA for the in-memory area is defined by the parameter
INMEMORY_SIZE . Set the area sufficiently large to accommodate all the columnar data identified in Step 1.

ALTER SYSTEM SET INMEMORY_SIZE = 10G SCOPE =SPFILE;
ALTER SYSTEM SET SGA_SIZE = 100G SCOPE=SPFILE;

■ Note the in-memory feature can also be invoked using the INMEMORY hint.

In the above change, when the in-memory area is allocated, the SGA area should also be increased
proportionately. If sufficient memory is not allocated to store the columnar data, Oracle will report the following
informational message in the alert log file:

Sun Aug 10 01:06:53 2014
Insufficient memory to populate table to inmemory area
Sun Aug 10 01:12:57 2014
Insufficient memory to populate table to inmemory area
Sun Aug 10 01:13:08 2014