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differences between local and dictionary mangaged tablespace [message #632461] Sun, 01 February 2015 05:29 Go to next message
m.abdulhaq
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Registered: April 2013
Location: Ajman
Senior Member
Hi,

Can someone explain me what is locally managed tablespace and dictionary managed tables and why locally is preferred ahead of dictionary managed with some good examples.I searched google but could not find any satisfactory answer.Appreciate if someone can help me on this.
Re: differences between local and dictionary mangaged tablespace [message #632466 is a reply to message #632461] Sun, 01 February 2015 06:31 Go to previous messageGo to next message
Michel Cadot
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What about a look at the documentation?

Quote:
I searched google but could not find any satisfactory answer


And what answers did you get (from where)?

Re: differences between local and dictionary mangaged tablespace [message #632469 is a reply to message #632466] Sun, 01 February 2015 07:16 Go to previous messageGo to next message
BlackSwan
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Location: SoCal
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With V8 Oracle DMT were produced as part of default database creation.
When V9 was the current release Oracle created LMT.
Since V10 & later LMT exist for default database creation.
To learn more Read The Fine Manual NEW FEATURES GUIDE for V9 point releases to read why LMT is preferable to DMT.
Re: differences between local and dictionary mangaged tablespace [message #632481 is a reply to message #632466] Sun, 01 February 2015 11:37 Go to previous messageGo to next message
m.abdulhaq
Messages: 243
Registered: April 2013
Location: Ajman
Senior Member
thanks Michael and Blackswan , i was reading oracle db concepts manual and there i came across following lines , i got confused over bitmap issue and how locally managed tablespace work.

Quote:


Tablespaces allocate space in extents. Tablespaces can use two different methods to
keep track of their free and used space:
■ Locally managed tablespaces: Extent management by the tablespace
■ Dictionary managed tablespaces: Extent management by the data dictionary




what does the following mean


Quote:

A tablespace that manages its own extents maintains a bitmap in each datafile to keep
track of the free or used status of blocks in that datafile. Each bit in the bitmap
corresponds to a block or a group of blocks. When an extent is allocated or freed for
reuse, Oracle changes the bitmap values to show the new status of the blocks. These
changes do not generate rollback information because they do not update tables in the
data dictionary (except for special cases such as tablespace quota information).
Locally managed tablespaces have the following advantages over dictionary managed
tablespaces:
■ Local management of extents automatically tracks adjacent free space, eliminating
the need to coalesce free extents.
■ Local management of extents avoids recursive space management operations.
Such recursive operations can occur in dictionary managed tablespaces if
consuming or releasing space in an extent results in another operation that
consumes or releases space in a data dictionary table or rollback segment.



Re: differences between local and dictionary mangaged tablespace [message #632482 is a reply to message #632481] Sun, 01 February 2015 12:07 Go to previous messageGo to next message
BlackSwan
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Location: SoCal
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It means LMT work fine.
LMT are more efficient than DMT they replaced.
Exactly what will you do differently after you decide you understand how LMT function internally since nothing you can do impacts LMT behavior?
Re: differences between local and dictionary mangaged tablespace [message #632486 is a reply to message #632481] Sun, 01 February 2015 13:56 Go to previous messageGo to next message
Michel Cadot
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Location: Nanterre, France, http://...
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You don't need to know how LMT works to use it (above all when you have no other choice).
Consider to investigate in more important points that are needed to work with Oracle.
For instance, do you master Data Concurrency and Consistency and Transactions?
These are the most important points to use Oracle.

Re: differences between local and dictionary mangaged tablespace [message #632495 is a reply to message #632486] Sun, 01 February 2015 22:01 Go to previous message
m.abdulhaq
Messages: 243
Registered: April 2013
Location: Ajman
Senior Member
thanks Michael and Blackswan, as of now i will move forwards with Data concurrency and transactions .
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