Hi Malcolm,
> To help conserve resources, should indexing be removed once used?
>
No. It would be very inefficient. Index creation is considered as expensive
operation which should be done usually at the beginning of the deployment,
> Can indexes become corrupted? If so, is there a method to determine the
> corruption and correct?
>
No (otherwise it's considered as a bug). Indexes are updated automatically
whenever data is updated.
> In some situations, can an index save memory? For instances, rather than
> conducting a full scan on a very large file to return data (which would
> require loading the file into memory), can using index prevent the full file
> load?
>
Yes! That's exactly why do we need them. For example, we got:
<persons>
<person name='Malcolm">...</person>
....
<person name='Ivan'>...</person>
</persons>
and want to get <person name='Ivan'> element. In naive straightforward
implementation we have something like:
doc('persons')/persons/person[@name eq 'Ivan']
it will scan ALL <person> elements to find the last one. For example, you
have millions of persons. Sedna would need to read from disc all chain of
blocks which contains <person> nodes.
But if you have index that query looks like:
index-scan("person-by-name", "EQ" "Ivan")
That's it. It's not direct access but it's much much better than full scan.
Sorry, I am not a dba type, so I am unaware of the problem space and
> techniques used in db development. I reviewed the Sedna technology papers,
> but I am still clueless.
>
No problems. Do not hesitate to ask any questions.
Ivan Shcheklein,
Sedna Team
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