Thanks for the help!
David On Oct 22, 2012, at 1:27 PM, Gajanan Chinchwadkar <[email protected]> wrote: > If an xpath expression has a predicate with value, then element range index > will be used, if available. > For example, in the following two cases a range index on xs:QName("title") > will be used: > a. /bookstore/book[title="XQuery Programming"] > b. /bookstore/book[title="XQuery Programming"]/author > > However, if there is no value in the predicate then the range index will not > be used: > c. . /bookstore/book[title] > > The same logic applies to where clause. If there is a value in the where > clause and a corresponding element range index, it will be used. > It is different in order by, where an index gets used even though there is no > comparison predicate and value. > > In 6.0.1-1, XPath based index can be defined. There are many situations when > MarkLogic server attempts to find matching path range index. Again in order > to use range index, there must be a comparison predicate in the query. > > Thanks, > > Gajanan > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Michael Blakeley > Sent: Monday, October 22, 2012 9:47 AM > To: MarkLogic Developer Discussion > Subject: Re: [MarkLogic Dev General] Range Index in Where Clause > > I would rephrase this as "does the evaluator ever use indexes for where > clauses?" If indexes are used at all, I would expect ranges to work too. And > with 6.0-1.1 the answer seems to be "yes" - but I would still recommend doing > as much as possible in XPath predicates. > > Here's a contrived test. In real life it would be very odd to have a > dls:created element in the main document, but since the range index comes > preconfigured it's handy for testing. > > declare namespace dls="http://marklogic.com/xdmp/dls";; > > xdmp:document-insert( > 'test/1', > element a { > element b { 'c' }, > element dls:created { xs:dateTime(xs:date('2012-12-01')) } }), > xdmp:document-insert( > 'test/2', > element a { > element b { 'c' }, > element dls:created { xs:dateTime(xs:date('2012-12-12')) } }) => () > > Now we have two documents that match the /a[b eq 'c'] portion of the > expression, but with different dsl:created values. Let's write a test query > that matches one, but not the other: > > declare namespace dls="http://marklogic.com/xdmp/dls";; > xdmp:query-trace(true()), > for $n in /a[ b eq 'c' ] > where $n/dls:created < xs:dateTime(xs:date('2012-12-12')) > return $n > > One document should match the dls:created constraint, and the other > shouldn't. The actual results match expectations, but that could be due to > filtering. Let's check the trace: > > 2012-10-22 09:06:18.661 Info: 8003-cq: at 4:11: Analyzing path for $n: > fn:collection()/a[b eq "c"] > 2012-10-22 09:06:18.661 Info: 8003-cq: at 4:11: Step 1 is searchable: > fn:collection() > 2012-10-22 09:06:18.661 Info: 8003-cq: at 4:11: Step 2 is searchable: a[b eq > "c"] > 2012-10-22 09:06:18.661 Info: 8003-cq: at 4:11: Path is fully searchable. > 2012-10-22 09:06:18.661 Info: 8003-cq: at 4:11: Gathering constraints. > 2012-10-22 09:06:18.661 Info: 8003-cq: at 4:14: Comparison contributed hash > value constraint: b = "c" > 2012-10-22 09:06:18.661 Info: 8003-cq: at 4:11: Step 2 predicate 1 > contributed 1 constraint: b eq "c" > 2012-10-22 09:06:18.661 Info: 8003-cq: at 4:14: Comparison contributed hash > value constraint: b = "c" > 2012-10-22 09:06:18.661 Info: 8003-cq: at 4:11: Step 2 predicate 1 > contributed 1 constraint: b eq "c" > 2012-10-22 09:06:18.661 Info: 8003-cq: at 4:11: Step 2 contributed 2 > constraints: a[b eq "c"] > 2012-10-22 09:06:18.661 Info: 8003-cq: at 5:9: Comparison contributed > dateTime range value constraint: dls:created < > xs:dateTime("2012-12-12T00:00:00") > 2012-10-22 09:06:18.661 Info: 8003-cq: at 4:11: Where clause contributed 1 > constraint for $n: $n/dls:created < xs:dateTime("2012-12-12T00:00:00") > 2012-10-22 09:06:18.661 Info: 8003-cq: at 4:11: Executing search. > 2012-10-22 09:06:18.667 Info: 8003-cq: at 4:11: Selected 1 fragment to filter > > That looks exactly as expected (aside from the duplication of b=c, anyway). > If we increment the date to the 13th or the 31st, both fragments match. If we > try to use a QName that doesn't have a range index, we lose the "Comparison > contributed dateTime range value constraint" line. So it seems clear that the > range index is used for the where-clause. > > Note that the same expression will be unsearchable according to xdmp:plan, > though. Presumably that's because the FLWOR expression taken as a whole is > unsearchable. That's understandable, but a little frustrating. > > Even knowing this, I would still recommend doing as much as possible in XPath > predicates. For one thing, you can use xdmp:plan instead of xdmp:query-trace. > > -- Mike > > On 22 Oct 2012, at 08:02 , David Sargeant <[email protected]> wrote: > >> I'm wondering if ML uses a range index in the where portion of a FLOWR >> expression where applicable. I could only find examples of 'order by'. >> Thanks. >> >> >> >> David >> >> _______________________________________________ >> General mailing list >> [email protected] >> http://developer.marklogic.com/mailman/listinfo/general > > _______________________________________________ > General mailing list > [email protected] > http://developer.marklogic.com/mailman/listinfo/general > _______________________________________________ > General mailing list > [email protected] > http://developer.marklogic.com/mailman/listinfo/general _______________________________________________ General mailing list [email protected] http://developer.marklogic.com/mailman/listinfo/general
