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From "Paolo Castagna (Created) (JIRA)" <>
Subject [jira] [Created] (JENA-144) An optimimsation for queries with FILTER ((?date > "..."^^xsd:dateTime) && (?date < "..."^^xsd:dateTime))
Date Fri, 21 Oct 2011 08:50:32 GMT
An optimimsation for queries with FILTER ((?date > "..."^^xsd:dateTime) && (?date
< "..."^^xsd:dateTime)) 

                 Key: JENA-144
             Project: Jena
          Issue Type: Improvement
          Components: TDB
            Reporter: Paolo Castagna

When TDB index literal values, if possible, it encodes the literal value directly into the
See NodeId.inline(Node node) method:
At query time, since there isn't an entry in the node table for values encoded in this way,
there is no need to perform lookups on the node table.

Let's consider this query pattern:

    ?s <> ?date .
    FILTER ( ( ?date > "2011-06-06T00:00:00Z"^^xsd:dateTime ) &&
             ( ?date < "2011-06-07T00:00:00Z"^^xsd:dateTime ) )

In this case the POS index will be used, doing a partial scan with a fixed P: [(P,0,0), (P+1,0,0))
where P is the NodeId corresponding to property used in the BGP (i.e. <>
in the example above).
However, if there are many subjects with a date, the filter expression needs to be evaluated
for all the date values. Even if those date values came straight out of the POS index and
not from the node table, this can take a while.

We could have a better range index scan which starts at a particular value (i.e. "2011-06-06T00:00:00Z"^^xsd:dateTime,
from the example above). The range index scan could be: [(P,D1,0), (P,D2,0)) where D1 and
D2 are the NodeId corresponding to the values specified in the FILTER expression.

It is also not clear how the optimizer could decide if this will be more selective than other
triple patterns.

See a couple of thread on jena-dev and jena-users mailing lists related to this:


(Or, maybe, this sort of optimisation is too specific, overly complicated... and a caching
layer would solve this and many other performance related issues! ;-))

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