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From "Paolo Castagna (Updated) (JIRA)" <>
Subject [jira] [Updated] (JENA-144) An optimisation for queries with FILTER ((?date > "..."^^xsd:dateTime) && (?date < "..."^^xsd:dateTime))
Date Wed, 16 Nov 2011 22:21:52 GMT


Paolo Castagna updated JENA-144:

    Summary: An optimisation for queries with FILTER ((?date > "..."^^xsd:dateTime) &&
(?date < "..."^^xsd:dateTime))   (was: An optimimsation for queries with FILTER ((?date
> "..."^^xsd:dateTime) && (?date < "..."^^xsd:dateTime)) )
> An optimisation for queries with FILTER ((?date > "..."^^xsd:dateTime) &&
(?date < "..."^^xsd:dateTime)) 
> ---------------------------------------------------------------------------------------------------------
>                 Key: JENA-144
>                 URL:
>             Project: Jena
>          Issue Type: Improvement
>          Components: TDB
>            Reporter: Paolo Castagna
>              Labels: optimization, performance
>   Original Estimate: 120h
>  Remaining Estimate: 120h
> When TDB index literal values, if possible, it encodes the literal value directly into
the NodeId. 
> 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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