An In-memory expression, or “hot” expression, enables frequently evaluated query expressions to be materialized in the In-Memory Column Store, for subsequent reuse. By default, the procedure DBMS_INMEMORY_ADMIN.IME_CAPTURE_EXPRESSIONS identifies and populates IM expressions.
Populating the materialized values of frequently used query expressions, into the In-Memory Column Store, greatly reduces the system resources required to execute queries, allowing for better scalability. The procedure, IME_CAPTURE_EXPRESSIONS, will capture and populate the 20 “hottest” expressions in the database for a specified time range.
An IM virtual column, is a value derived by evaluating an expression. IM virtual columns improve query performance by avoiding repeated calculations. Also, the database can scan and filter IM virtual columns, using techniques such as SIMD vector processing.
Before 12.2, the columnar format was only available In-Memory, meaning that after a database restart, the In-Memory Column Store would have to be populated. This multiple step process, converted traditional, row formatted data into the compressed columnar format and placed in-memory.
Now, In-Memory Column Store optimizes the compressed columnar population of database objects (tables, partitions, and subpartitions) in the...
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