How does one prevent tablespace fragmentation

That is, the copying of the contents of one table to another while the original table is updated. Changes to the original table were tracked and applied to the new table.

Physical and logical attributes of the table could be changed during this online operation, thus allowing an online reorganization. Prior to Oracle9i, reducing fragmentation was more difficult. The general recommendation was to avoid fragmentation through careful planning. But the usual way to solve fragmentation was to reorganize a table by exporting the table, dropping it, and importing it.

The data was unavailable while the table was in the process of being reorganized. If you now ask for an initial extent of K, then you will be allocated two extents of K each. Ask for K, and you'll get 3 K extents, and so on. And since every extent is always going to be K, you've now got entirely consistent extent sizes, and zero possibility of ever encountering fragmentation. One more thing to say about this idea of consistent extent sizes: it does mean that you need to plan your tablespaces more carefully.

If all you had was a tablespace allocating K extents, it would be a bit sad to then use it to house the "States and Territories of Australia" lookup table which happens to consist of 8 records. That would be a mammoth waste of space -which is all fragmentation itself is at the end of the day. What you really need, of course, is a range of tablespaces, some allocating 16K extents, some 64K, some K, some K and so on. Then all you have to do is house the right segment in the right sort of tablespace.

Diagnosis is relatively easy. Incidentally, if you're using Oracle Enterprise Manager, the Tablespace Map utility gives a nice visual display of extent allocations within a tablespace, and fragmentation leaps out at you as lots of little bits of white space.

Curing it is tricky. That would allow EMP, requesting a 5 block extent, to acquire it from that piece of free space. Notice what coalesce didn't do, though: It did not merge the block chunk with the 2-block chunk at the end to generate a single block piece of free space.

Coalesce only merges adjacent pieces of free space. That would indeed achieve the following sort of result: Of course, having to truncate the EMP table means it's unavailable for use by anyone until the import has finished, so it's not exactly a high-availability solution. Regards, Santosh. September 27, - pm UTC. Sir, I got the term from the below links: jonathanlewis.

September 28, - am UTC. What other questions do you have. But in short - LMT's have nothing to do with block space management. Hi Tom, Still a little bit confused about 'tablespace fragmentation', hope you can find some time to elaborate I am on 11g with LMT.

Basically my question is if i see below, can i say there is 'tablespace fragmentation'? Also during my testing in terms of tablespace fragmentation, i got some other questions, hope you can help to answer at the same time. They are inside my below test script, started with Q Q1,Q Or it is possible to allocate extent in different file even they both have free space? There is no data inserted, should not take space i think. Should not it be used up? I know it is somehow due to i create some small table before and drop it, but not quite clear.

Because if i did not create small table before, but just create a big table as below script , when check free space, no rows return So it really make me believe it is 'tablespace fragmentation' in Q5. March 26, - am UTC. This typically only happens with dictionary managed tablespaces. It can never happen with locally managed tablespaces with uniform extent sizes and rarely happens with locally managed tablespaces with system allocated extents.

For that one, we tend to put the first N extents "together" if possible so that if the segment is dropped later - we get a bigger chunk of free space together they are all 64k extents in many cases q2 round robin. But when the extent size bumps up to blocks - we start going round robin to spread the data out. If you insert a billion rows into a table and rollback - you'll have had to of allocated space for one billion rows.

And since a rollback is a logical operation it'll delete each row inserted, it is not like recovery - it cannot release allocated space.

A reader, March 26, - am UTC. Hi Tom, Regarding your last response above I just put in a row, commit and so on. March 27, - am UTC. Tablespace fragmentation Oracle This is clear to me. But can fragmentation happen in case of segment updates, deletes and truncates. When segment is looking for next extent then it will find there is no contiguous free space available. May 10, - am UTC.

After that - they are meaningless. Your mixing of E and B is incorrect. An extent is a collection of blocks, it doesn't make sense to mix them like that. An extent either belongs to a segment and is entirely NOT free or it does not and is entirely free. Table have only 60 rows so I want to remove fragmentation so I moved table within tablespace but fragmentation not removed. It showing still same size 4gb. August 16, - am UTC. What are synonyms used for?

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