Oracle Database In-Memory – simple example
In a previous post, I showed how to enable and increase the memory allocation for use by Oracle In-Memory. That example was based on using the Pre-built VM supplied by Oracle.
To use In-Memory on your objects, you have a few options.
Enabling the In-Memory attribute on the EXAMPLE tablespace by specifying the INMEMORY attribute
SQL> ALTER TABLESPACE example INMEMORY;
Enabling the In-Memory attribute on the sales table but excluding the “prod_id” column
SQL> ALTER TABLE sales INMEMORY NO INMEMORY(prod_id);
Disabling the In-Memory attribute on one partition of the sales table by specifying the NO INMEMORY clause
SQL> ALTER TABLE sales MODIFY PARTITION SALES_Q1_1998 NO INMEMORY;
Enabling the In-Memory attribute on the customers table with a priority level of critical
SQL> ALTER TABLE customers INMEMORY PRIORITY CRITICAL;
You can also specify the priority level, which helps to prioritise the order the objects are loaded into memory.

A simple example to illustrate the effect of using In-Memory versus not.
Create a table with, say, 11K records. It doesn’t really matter what columns and data are.
Now select all the records and display the explain plan
select count(*) from test_inmemory;

Now, move the table to In-Memory and rerun your query.
alter table test_inmemory inmemory PRIORITY critical;
select count(*) from test_inmemory; -- again

There you go!
We can check to see what object are In-Memory by
SELECT table_name, inmemory, inmemory_priority, inmemory_distribute,
inmemory_compression, inmemory_duplicate
FROM user_tables
WHERE inmemory = 'ENABLED’
ORDER BY table_name;

To remove the object from In-Memory
SQL > alter table test_inmemory no inmemory; -- remove the table from in-memory
This is just a simple test and lots of other things can be done to improve performance
But, you do need to be careful about using In-Memory. It does have some limitations and scenarios where it doesn’t work so well. So care is needed
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September 13, 2022 at 1:10 pm
[…] Brendan Tierney shows us how to work with Oracle’s In-Memory capabilities: […]
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