8.1.2 In-Memory Columnar Caching on Storage Servers

Oracle Exadata System Software release 12.2.1.1.0 introduced the support for In-Memory Columnar Caching on Oracle Exadata Storage Servers for Exadata Hybrid Columnar Compression tables. Oracle Exadata System Software 18c (18.1.0) extends the support for In-Memory Columnar Caching on storage servers for additional table types, specifically uncompressed tables and OLTP compressed tables.

By extending the Database In-Memory format for uncompressed tables and OLTP compressed tables, smart scan queries on more table types can benefit from fast vector-processing in-memory algorithms on data stored in the storage flash cache. With this format, most in-memory performance enhancements are supported in Smart Scan including joins and aggregation. Database In-Memory format is space efficient and usually takes up less space than uncompressed or OLTP compressed formats. Storing data in Database In-memory format results in better storage flash cache space utilization.

Rewriting data from the traditional uncompressed or OLTP compressed format to Database In-Memory format is very CPU intensive. Oracle Exadata System Software has built-in intelligence to cache data in Database In-Memory format for regions that are not modified frequently.

Data from normal (unencrypted) as well as encrypted tablespaces can be cached in the in-memory columnar cache format.

Just as with Oracle Database In-Memory, the new Database In-Memory format is created by a background process so that it does not interfere with the performance of queries.

This feature is enabled by default when you configure the INMEMORY_SIZE database initialization parameter; no further configuration is required to use this feature. If INMEMORY_SIZE is not configured, then uncompressed tables and OLTP compressed table data is cached in Flash Cache in its native format and not in the Database In-Memory columnar format.

If you need to disable this feature, you can use a new DDL keyword CELLMEMORY with the ALTER TABLE command. See "Enabling or Disabling In-Memory Columnar Caching on Storage Servers" in Oracle Exadata System Software User's Guide.

Minimum requirements:

• Oracle Exadata System Software 18c (18.1.0)

• Oracle Database 12c release 1 (12.1.0.2) version 12.1.0.2.161018DBBP or Oracle Database 12c release 2 (12.2.0.1)

• Patch for bug 24521608 if using Oracle Database 12c release 1 (12.1.0.2)

• (Recommended) Patch for bug 26261327 (Enables better reverse offload functionality for complex queries)