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Rebuilding bitmap indexes help achieve space and get some free space?

845836
845836 Member Posts: 96
edited May 26, 2011 5:14PM in Advanced Compression
Hi,
I have a tablespace which is 90% full. I will be able to add space only after 3-4 days. But right now I need some free space.

Does rebuilding or COALESCE help achieving some free space?


Thanks,
Gangadhar

Answers

  • Hi Gangadhar,

    Rebuilding bitmap indexes are not supposed to give you much free space after rebuilding, comparing to b-tree indexes. Is this your only option for freeing up space?

    LMC
    Luis Moreno Campos-Oracle
  • 845836
    845836 Member Posts: 96
    It was a b-tree index and it did free up 5% space. Now I have 15% free space and can manage for next 4-5 days.

    But good to know about bitmap indexes doesn't free up much space compared to b-tree. So when its bitmap index adding space is the only option?
  • Bitmap indexes are not supposed to belong to tables being updated frequently, they usually take up much less space than b-tree when the column cardinality is low. So when something is small, for much space it can save, it will never be as much as something bigger.
    But remember that if you are rebuilding indexes in the same tablespace you will need temporary space inside that same tablespace to rebuild them, so it might be the case that the free space you have right now it's not even enough for the rebuilding process.

    LMC
    Luis Moreno Campos-Oracle
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