Philip There is no function in Oracle (up to 11g currently) that will allow you to reduce the size of the undo tablespace. Sometimes you will need to free up space and the best way to get it will be to reduce the size of the undo tablespace. The way to do this is basically to …
When data is changed in the oracle database, the information needed to undo the changes is recorded so that the change can be undone (Rolled back). The record is basically just the original information. Information is recorded in rollback segments and the undo tablespaces. This information is also used to provide read consistency which allows long running transactions …
When a redo log file fills up it switches to the next file. This is called a log switch. The log switch always causes a checkpoint to occur. This flushes all dirty buffers from the log cache. (writes modified data to disk) If archiving is on, the old log file id archived. The new log …
One of the most important ideas in Oracle is that your data is safe. It is protected from corruption and also from system crashes. One of the most important ways that it does this is through the Redo logs. A Redo log record is written to describe the changes every time some data is changed …
When the data in a oracle database needs to be changed, it has to be done quickly. Accessing the data files on disk is slow and so, all changes in the Oracle database are carried out in the buffer cache and are only written to files at a later point by the DBWR. The buffer …
Oracle is a multi user system and as such, multiple processes need to access the database at the same time to perform both reads and writes. Each one needs to get a consistent view of the data – one that does not change during a tranaction. Oracle ensures that the data that a process gets …
In Oracle, the Undo records allow data that is being modified to be accessed. Oracle uses row level locking to prevent two processes from trying to update the same data at the same time. Only the rows being modified are locked. This means that the rest of the table can still be modified while a …
The Users server process is the process that handles the users requests to the oracle database. When the user requests a add, update or delete of data in the database, the server process modifies the data from the buffer cache, not the actual data files. The DBWR (Database Writer) process is the only process that …
Reading from the Oracle RDMS is done by the users server process Once a query is submitted, the users server process first determines if data is in the buffer cache of the SGA (System Global Area) memory area. If the data is not already in the buffer cache, Oracle reads the data from the data …