Adding Logfiles To add a redo log, the following command is used: ALTER DATABASE database name ADD LOGFILE THREAD y GROUP n (file specification, file specification) SIZE x; or: ALTER DATABASE dat...
The database writer process (often referred to as DBWR from the times when only one was allowed, but more properly referred to as DBWn) is responsible for asynchronously writing out dirty buffers in t...
Sometimes, data blocks are read in the database, and are infrequently reused. Often in a database we also have data blocks that are of frequent use (hot blocks). It is for these types of database bloc...
Processing SQL Statements The first time a select query is executed inside the Oracle engine, the statement will generally need to proceed through 4 different stages in order to return results back to...
Log file space/switch waits Log file space/switch waits occur when a redo log entry cannot be made. A redo log cannot be written to when: there is no free space in the redo log buffer, or it is i...
Once the application and memory areas have been tuned, the next performance bottleneck can be the disk subsystem. A number of performance indicators can suggest a need to improve Oracle disk I/O. A ma...
There are several ways to look at what's happening in a multi-threaded server environment. Using operating-system commands, you may be able to see a list of the dispatcher and shared server processes ...
RAC uses cluster interconnects to transfer blocks between the nodes participating in the cluster. A block transfer occurs when a user session connected to one instance requests a block being held in t...
Improving Redo Log Writer Performance Redo logs contain details of transactions that may not yet have been written to the data files. The primary purpose of the redo logs is to allow for the recove...
The Parallel Query Option (PQO) is best used for systems where large, intense queries are being performed or where large amounts of data are being loaded, indexed and queried, such as in data warehous...
While you initially configure MTS in your instance parameter file, there are some changes that you can make while the instance is running. Using the ALTER SYSTEM command, you can manually adjust the n...
Just as the architecture of the database buffer cache has changed dramatically from release to release, so too have the effectiveness of the tools Oracle supplies to assist with tuning the database bu...
