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Hello Mark,

Am 30.03.2023 um 14:48 schrieb Mark Murphy <jmarkmurphy@xxxxxxxxx>:

We have a client who wants to rebuild indexes, just because they haven't
been built for a long time (3-4 years). They think it will improve
performance. I've never rebuilt indexes to improve performance. Does anyone
have an opinion on this?

In theory, any object might become fragmented on disk over time. Recreating indexes thus might increase performance.

If this theoretical increase is relevant in practice, or even measurable, I can't tell. This heavily depends on the hardware details such as disk count (and type: mechanical or SSD) of the affected ASPs, amount of RAM, etc., and on the size of the tables and indices themselves.
Probably there's also a penalty for writes, eventhough there's enough RAM to keep the index there (for reads). This also depends on usage of the tables in question, and if journalling is in use (which AFAIK buffers table writes in RAM).

Not an easy to answer question, as you can see. Being a while in this group, I can't recall coming across the topic of defragmentation on IBM i.

I disagree with Rob. I can't see how this might end up being a shoot in the foot.

:wq! PoC

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