Oracle Indexes The degree to which indexes help performance depends partly on the selectivity of the data.High selectivity – Few rows match the index valueLow selectivity – like Country name returns many rows from the index If data is selective but the rows are not stored near each other in the table, many blocks may …
If you are having trouble getting your head around the basics of Oracles Architecture, this video does a good job of simplifying things and making it easy to remember by breaking it down and describing it via everyday examples. You can skip to around 2:30 for the real start of the video. Notes; Datafiles – …
It is possible to use operating system commands such as rm on linux to delete RMAN backup files and generally recover from it, however you are far better using built in RMAN commands to do this. $ rman target / NOCATALOG First, check that all backup files are still available. This will show whether files …
Great webinar on Oracle 12c plugable databases. Skip to 8 minutes for the start of the actual presentation.
[embedplusvideo height=”356″ width=”584″ standard=”http://www.youtube.com/v/L_2TfSHotsY?fs=1″ vars=”ytid=L_2TfSHotsY&width=584&height=356&start=&stop=&rs=w&hd=0&autoplay=0&react=1&chapters=¬es=” id=”ep6822″ /] Watch the rest of this series: Part 1 Part 2 Part 4 Notes: Initilisation params for the Buffer cache: db_cache_size db_block_size It is very helpfull if the buffer block size is a multiple of your operating system block size. The Buffer cache is controled with a Least Recently Used …
[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 …