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Re: What is persisted index?

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Hmm.. hmm... weired things happening here in SCN.

 

The Rules of Engagement (http://scn.sap.com/docs/DOC-18590) document is not accessible anymore??

 

Anyhow, didn't we have that rule to use our real names here?

If that's your real name "cc 122010" I am actually sorry for you.

 

So, persisted indexes?

It's a rather straight forward thingy. Up until SPS 7 the default behavior for inverted indexes on column store table columns was: re-create them after loading the column to memory.

As all the information we need to create the index is in that column, there is no need to store it on disk.

 

That's fine until you have

a) a rather large indexes that take long to create (keep in mind, the inverted indexes are pretty similar to the main/value vector and compression is applied to the inverted index as well)

and/or

b) the column on which the inverted index has been created gets unloaded and loaded rather often.

 

In such a scenario it might be better to have the index also stored on disk.

Also, and that is a major reason, the index is immediately usable again after a fail-over to a standby node.

 

With SPS 7 the default behavior changed, so that the inverted indexes get stored to disk as well.

Hope that answers the question.

 

- Lars


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