New Features for Oracle Database 12cR2 In-Memory

Oracle 12cR2 release introduced many new features for the in-memory database technology, the following is some of the new features introduced:

Dynamically increase In-Memory area on the fly

Starting in 12.2, it is possible to increase the size of the In-Memory area on the fly, by increasing the INMEMORY_SIZE parameter using ALTER SYSTEM command. Also, worht mentioning is that The INMEMORY_SIZE parameter must be increased by 128MB or more in order for this change to take effect. However, It is not possible to shrink the size of the In-Memory area on the fly.

In-Memory FastStart

Enabling In-Memory FastStart (IM FastStart) the system will checkpoints the IMCUs from the IM column store to the FastStart area on disk. Consequnetly, when database restarts takes place, data is populated via the FastStart area rather than from the base tables.

Note that FAST_START_TBS is a dedicated tablespace configured for FastStart,is allowed for each PDB or non-CDB.the FastStart tablespace should be at least twice the size of the INMEMORY_SIZE setting.

CREATE TABLESPACE FAST_START_TBS DATAFILE
‘D:\APP\EMAD\VIRTUAL\ORADATA\ORACLE\FASTSTARTD01.DBF’ SIZE 400M
LOGGING FORCE LOGGING ONLINE PERMANENT BLOCKSIZE 8192
EXTENT MANAGEMENT LOCAL AUTOALLOCATE DEFAULT
NOCOMPRESS SEGMENT SPACE MANAGEMENT AUTO;

SQL> BEGIN dbms_inmemory_admin.faststart_enable(‘FAST_START_TBS’); END;

So, basically The FastStart area defines what data is loaded when the database reopens. Population of data is still controlled by the “priority” settings, it won’t affect it.

SQL> SELECT * FROM V$INMEMORY_FASTSTART_AREA;

inmem1

In-Memory Expressions

In-Memory Expressions provide the ability to materialize commonly used expressions in the In-Memory column store. Materializing these expressions will improve the query performance by preventing the re-computation of the expression for every row. Also, it enables us to take advantage of all of the In-Memory query performance optimization when we access them.

* Analytic queries often contain complex expressions in the select list or where clause predicates that need to be evaluated for every row processed by the query

* The evaluation of these complex expressions can be very resource intensive and time consuming

* In-Memory Expressions greatly improve the performance of analytic queries that use computationally intensive expressions and access large data sets

* In-Memory expressions speed queries of large data sets by pre-computing computationally intensive expressions

In-Memory Virtual Columns

user-defined virtual columns can now be populated in the In-Memory column store. Virtual columns will be materialized as they are populated and since the expression is evaluated at population time it can be retrieved repeatedly without re-evaluation.

To illustrate:

SQL> alter system set inmemory_virtual_columns=ENABLE scope=spfile;

inmem2

CREATE TABLE HR.EMPLOYEE_SALES (
employee_id NUMBER(6) PRIMARY KEY ,
first_name VARCHAR2(10),
last_name VARCHAR2(10),
salary NUMBER(8,2)
);

The target query against the table will be:

SQL> select employee_id,last_name,salary,(salary/12) as monthly_sal, 3*(salary+2000) as bonus from HR.EMPLOYEE_SALES order by bonus;

SQL> ALTER TABLE HR.EMPLOYEE_SALES ADD monthly_sal AS (salary/12);
SQL>ALTER TABLE HR.EMPLOYEE_SALES ADD bonus AS (3*(salary+2000));

SQL> ALTER TABLE HR.EMPLOYEE_SALES INMEMORY PRIORITY HIGH;

SQL>DBMS_INMEMORY_ADMIN.IME_CAPTURE_EXPRESSIONS(‘CURRENT’);
SQL> EXEC DBMS_INMEMORY_ADMIN.IME_POPULATE_EXPRESSIONS();

SQL>SELECT OWNER, TABLE_NAME, COLUMN_NAME, SQL_EXPRESSION
FROM DBA_IM_EXPRESSIONS;

 

 

 

 

 

 

 

 

 

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