What Makes Oracle Exadata So Great

Article By: Richard Niemiec

With the acquisition of Sun, a paradigm shift occurred in the database market, the hardware world, and the IT industry. While this shift is just beginning, the early tremors are showing that the major shift is coming and will be big over the next decade. Here are a few points about what is coming. Exadata is hardware that combines the power of the database, while leveraging features Oracle added at the hardware level that other hardware providers will not be able to replicate easily (or at all). Some of the major Exadata benefits include:

Flash Cache The Flash Cache is comprised of solid-state disks (information stored on chips—over 5 terabytes in a full rack), which is around 20× to 50× faster than disks (depending on the disks). The Flash Cache caches hot data (data frequently used). It does this as the last step (so it returns data to the user first and then caches it for the next time based on the settings you give it).

NOTE

The Flash Cache memory (hardware/chips) is not the same as the Database Flash Cache. You can use Database Flash Cache with the Oracle Database 11g and Oracle RAC 11g. The Database Flash Cache is an optional area that you can add if your database is running on Solaris or Oracle Linux. It is a file-based extension of the SGA-resident buffer cache (similar to a swap area), providing a level-2 cache for database blocks. The file is used as the database is aged out of the SGA. To get more information, see the initialization parameter DB_FLASH_CACHE_SIZE.

Storage index A storage index utilizes minimum/maximum (min/max) values to help queries run faster. A performance gain of 10× is common with storage indexes. They primarily maintain summary information about the data (like metadata in a way). The memory structure resides at the cell level (disk/storage cell). For a cell (a unit of storage), the min/max values for up to eight queried table columns are stored in that Exadata storage cell and in the storage index. So a storage index is an index of how the data is stored across cells (like the min/max values for partitions). When a query is run against a table, the storage index is checked to see which cells need to be accessed to retrieve the data. Oracle searches data based on the min/max for various columns and eliminates I/Os where there is no match. The process is 100 percent transparent to the user. It is performed at the hardware level and typically has one index for every 1M of disk. No setup is required; Oracle does this internally and automatically. Storage indexes can also provide a huge benefit for highly skewed data. The storage index offers quick access to the highly selective values, whereas the normal Exadata offloading handles the nonselective values.
Smart scans Smart scans are performed internally at the hardware level by Oracle and 10× savings are common. Oracle filters things based on the WHERE clause (predicates) and filters on row/column/join condition. No setup is required; Oracle does this internally and automatically.
Hybrid Columnar Compression (HCC) Hybrid Columnar Compression (HCC), also known as Exadata Hybrid Columnar Compression (EHCC), is data that is organized by a hybrid of column and row formats and then compressed. A performance gain anywhere from 10× to 30× is common. The tables are organized in Compression Units (CU), which contain around 1000 rows (more or less depending on the amount of data in the rows). CUs span many blocks. HCC is good for data that is bulk loaded, but it’s not built for OLTP or single block-read operations. It is primarily built for Data Warehouses and Queried Data and not for frequently updated data. Compared to Gzip/Bzip2, HCC typically has 2× the compression and is 10× faster.
Enterprise Manager Grid Control Oracle Enterprise Manager Grid Control has a specific plug-in for Exadata, which allows you to manage and view many of the advantages that Oracle provides with Exadata easily. It is also a good way to ensure things are working properly and efficiently.
Enterprise Manager Exadata Simulation This allows you to check the benefits of Exadata before implementing it by running a simulation on your current system. This feature is a part of SQL Performance Analyzer, which is a part of Oracle Real Application Testing. Additional licensing is required.
I/O Resource Manager Oracle’s latest I/O Resource Management (IORM) tool can be used with Exadata to manage multiple workloads and set resources as you deem necessary for each database, user, or task. IORM gives you the capability to manage many systems easily with a single machine.
Security Secure encrypted backup with change tracking file (which is much faster), in which the storage nodes offer hardware decryption acceleration. Exadata takes advantage of CPU hardware decryption acceleration with AES-NI, so you can encrypt and decrypt even when using TDE tablespace or column encryption (encrypted data is now decrypted before Smart-Scan is applied).
Utilities Cellcli is a command-line interface for queries at the hardware level and for monitoring various health metrics for individual cells; DCLI is for querying multiple cells, and ADR Command Interpreter (ADRCI) is for diagnostics.