No of Datafiles needed in single tablespace ?

hi,
i have one tablespace of size 120gb with 23 datafiles in which first 19 datafiles are size with 2gb each. and rest data files are size with around 28 gb.
Recently i heard that by keeping more no of datafiles will affect the performance of Database . so my question is what are the advantage and disadvantage of keeping more no of
datafiles in single tablespace and how can i merge small data files of 2 gb ?
Regards,
Mithun Mathew
Oracle DBA

After going through couple of links provied by google i made a note on this issue :
Optimizer does not consider number of data files when selecting execution path. Also as a general rule, you do not deal with I/O performance at tablespace level. You cannot stripe the contents of a tablespace across multiple datafiles. This need to be dealt with at a lower level (like inside Oracle ASM).
Advantages: (More Datafiles)
1.By using more than one datafile per tablespace, you can spread data over many different disks to distribute the I/O load and improve performance.
2.Easy and faster restoration and recovery. The more datafiles for a given amount of data, some recovery scenarios will be faster due to having to restore/recover a smaller file.
3.Less chances of encountering 2gb
issue.(http://www.fors.com/velpuri2/Oracle%20block%20structure/2gb)
4.Having multiple datafiles per tablespace facilitates the adoption of a uniform datafile size policy, which in turn facilitates disk load rebalancing.
5.For file system based databases, having multiple datafiles may reduce the risk of contention for the operating system's datafile read/write locks (inode locks).
6.If any corruption happens in a datafile, then there is less data loss chances in compare to one or less datafile.
Disadvantages: (More Datafiles)
1.We can not have BigFile Tablespace's advantages.
2.Tough managebility and portability.
3.Putting tablespace offline will offline all the datafiles, which will stop other applications/of its parts unnecessarily.
4.More datafiles for DBWR for writting and more files for RMAN to backup.
5.Many datafiles are opens when we online tablespace; means many file handlers for OS at kernel side.
6.We have to carefull to create rollback segments because, never create rollback segments using multiple datafiles within a single tablespace.
7.The more datafiles, the more time required to do checkpoints and such, because every file has to have its header updated.
8.More entries in data dictionary, control file entries more file structs in SGA vs less or 1.
Regards
Girish Sharma

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Message was edited by:
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No of Datafiles needed in single tablespace ?

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