Hello Ivan,
Thank you very much for you time and response!
This will help us out a great deal in our development and producing a better
product for our clients.
Malcolm
From: Ivan Shcheklein [mailto:shchekl...@gmail.com]
Sent: Thursday, July 07, 2011 2:31 PM
To: Malcolm Davis
Cc: sedna-discussion@lists.sourceforge.net
Subject: Re: [Sedna-discussion] Sedna indexing usage
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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