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I have huge table in DB with estimated size 7 GB (I saw that using DB2CC and did the action Estimate Size for that Table).

In estimate size dialog I noticed that two of my indexes for that table have very huge size - one is 4 GB and other is 2 GB.

How is possible that index can take so much disk space and is this regular behavior?

Thank you

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Indexes essentially duplicate data on disk. The idea though is the tradeoff in performance. Extra disk used, but faster response looking up data.

But since indexes do cost extra disk, one should weigh carefully whether or not the index is actually needed. If not needed, it will cost that extra disk and may even cost you in terms of performance (especially on inserts, updates, and deletes).

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  • Hi Chris, this is out of the box system indexes for that table and cannot be deleted. So basically please conclude - nothing we can do, this is regular behavior right?
    – Dejan
    Feb 18, 2015 at 14:09
  • If it is an out of the box system, then if you have concerns I would discuss it with the vendor. Perhaps they can address your concerns by removing the index, or compressing it, etc. Feb 18, 2015 at 16:30
  • Hi Crris , sorry can you please assist me with these two question if you are in position to help? Thanks dba.stackexchange.com/questions/154338/… dba.stackexchange.com/questions/154230/…
    – Dejan
    Nov 5, 2016 at 17:35

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