Oracle Basics - Interesting things

The characteristics of datafiles are:

• A datafile can be associated with only one database.
• Datafiles can have certain characteristics set to let them automatically extend when the database runs out of space.

In a UNIX environment,
most Oracle processes are part of one master Oracle process, rather than being individual processes.

On Windows NT,
All processes consist of at least one thread. A thread is an individual execution within a process. Threads enable concurrent operations within a process so that a process can run different parts of its program simultaneously on different processors.

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Database Buffer Cache of the SGA

Database buffers store the most recently used blocks of data. The set of database buffers in an instance is the database buffer cache. The buffer cache contains modified as well as unmodified blocks. Because the most recently (and often, the most frequently) used data is kept in memory, less disk I/O is necessary, and performance is improved.

Redo Log Buffer of the SGA

The redo log buffer stores redo entries--a log of changes made to the database. The redo entries stored in the redo log buffers are written to an online redo log, which is used if database recovery is necessary. The size of the redo log is static.

Shared Pool of the SGA

The shared pool contains shared memory constructs, such as shared SQL areas. A shared SQL area is required to process every unique SQL statement submitted to a database. A shared SQL area contains information such as the parse tree and execution plan for the corresponding statement. A single shared SQL area is used by multiple applications that issue the same statement, leaving more shared memory for other uses.

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Dig in SMON

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  A control file contains information such as:

• The database name
• The timestamp of database creation
• The names and locations of associated datafiles and online redo log files
• Tablespace information
• Datafile offline ranges
• The log history
• Archived log information
• Backup set and backup piece information
• Backup datafile and redo log information
• Datafile copy information
• The current log sequence number
• Checkpoint information

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