[embedplusvideo height=”328″ width=”584″ standard=”http://www.youtube.com/v/nNGLyWIPPTQ?fs=1″ vars=”ytid=nNGLyWIPPTQ&width=584&height=328&start=&stop=&rs=w&hd=0&autoplay=0&react=1&chapters=¬es=” id=”ep8443″ /] Watch the earlier parts first: Part 1 Part 2 Part 3 Notes: Oracle Processes Dbwr Database Writer Writes from the SGA to the data files Does deffered writes like a hotel room clerk kicks blocks out to disk when new data needs free blocks Lgwr Log …
[embedplusvideo height=”328″ width=”584″ standard=”http://www.youtube.com/v/wmc9uxNW99E?fs=1″ vars=”ytid=wmc9uxNW99E&width=584&height=328&start=&stop=&rs=w&hd=0&autoplay=0&react=1&chapters=¬es=” id=”ep5503″ /] Check out part 1 first. Notes: Online Redo Logs Contains Redo and Undo info DML Inserts/Deletes DDL – Create alter drop Commits Need at least 2 files/groups Should be multiplexed each on different devices and controlers When each file fils, next one is started and old one is archived (if …
[embedplusvideo height=”328″ width=”584″ standard=”http://www.youtube.com/v/addFo5FMzkg?fs=1″ vars=”ytid=addFo5FMzkg&width=584&height=328&start=&stop=&rs=w&hd=0&autoplay=0&react=1&chapters=¬es=” id=”ep3446″ /] There are 3 essential elements of any database system Datafiles – storage Memory – in oracle its the SGA Processes – To operate on the data files and memory Storage Datafiles Contains data Tables Indexes Undo segments (used to be rollback segments) Temporary files Oracle is easy as DIRT …
In much the same way as with the Undo tablespace, you may want to reduce the size of the Temp tablespace in Oracle to reclaim space. 11g —- ALTER TABLESPACE [tbsp_name] SHRINK SPACE KEEP 30M; 10g and earlier —————— Unfortunatly, if the temp tablespace is full (as will be the case if it has …
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 …