That sounds great, Ron. Not sure why I didn't see the effect of the
indexing before, but I will revisit this soon with renewed hope!
-Mike
Ron Avnur wrote:
You can create range indexes on properties: both server-maintained
properties and the ones you add on your own.
I created a range index on the prop:last-modified property with the
following settings:
scalar type: dateTime
namespace uri: http://marklogic.com/xdmp/property
localname: last-modified
I then executed the following query:
xdmp:query-trace(true()),
(for $t in xdmp:document-properties()//prop:last-modified
order by $t descending
return <node uri="{base-uri ($t)}">{xs:dateTime(data($t))}</node>)[1],
xdmp:query-meters()
It returned:
<node uri="new2.xml">2007-06-14T10:07:55-07:00</node>
<qm:query-meters xsi:schemaLocation="http://marklogic.com/xdmp/query-meters query-meters.xsd"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
xmlns:qm="http://marklogic.com/xdmp/query-meters";>
<qm:elapsed-time>PT0.174421S</qm:elapsed-time>
<qm:requests>1</qm:requests>
<qm:list-cache-hits>12</qm:list-cache-hits>
<qm:list-cache-misses>0</qm:list-cache-misses>
<qm:in-memory-list-hits>0</qm:in-memory-list-hits>
<qm:expanded-tree-cache-hits>4</qm:expanded-tree-cache-hits>
<qm:expanded-tree-cache-misses>0</qm:expanded-tree-cache-misses>
<qm:compressed-tree-cache-hits>0</qm:compressed-tree-cache-hits>
<qm:compressed-tree-cache-misses>0</qm:compressed-tree-cache-misses>
<qm:in-memory-compressed-tree-hits>0</qm:in-memory-compressed-tree-hits>
<qm:value-cache-hits>2</qm:value-cache-hits>
<qm:value-cache-misses>2</qm:value-cache-misses>
<qm:regexp-cache-hits>0</qm:regexp-cache-hits>
<qm:regexp-cache-misses>0</qm:regexp-cache-misses>
<qm:link-cache-hits>0</qm:link-cache-hits>
<qm:link-cache-misses>0</qm:link-cache-misses>
<qm:fragments-added>0</qm:fragments-added>
<qm:fragments-deleted>0</qm:fragments-deleted>
<qm:fs-program-cache-hits>1</qm:fs-program-cache-hits>
<qm:fs-program-cache-misses>0</qm:fs-program-cache-misses>
<qm:db-program-cache-hits>0</qm:db-program-cache-hits>
<qm:db-program-cache-misses>0</qm:db-program-cache-misses>
<qm:fs-main-module-sequence-cache-hits>0</qm:fs-main-module-sequence-cache-hits>
<qm:fs-main-module-sequence-cache-misses>0</qm:fs-main-module-sequence-cache-misses>
<qm:db-main-module-sequence-cache-hits>0</qm:db-main-module-sequence-cache-hits>
<qm:db-main-module-sequence-cache-misses>0</qm:db-main-module-sequence-cache-misses>
<qm:fs-library-module-cache-hits>0</qm:fs-library-module-cache-hits>
<qm:fs-library-module-cache-misses>0</qm:fs-library-module-cache-misses>
<qm:db-library-module-cache-hits>0</qm:db-library-module-cache-hits>
<qm:db-library-module-cache-misses>0</qm:db-library-module-cache-misses>
<qm:fragments>
<qm:fragment>
<qm:root xmlns="http://marklogic.com/xdmp/property";>properties</qm:root>
<qm:expanded-tree-cache-hits>4</qm:expanded-tree-cache-hits>
<qm:expanded-tree-cache-misses>0</qm:expanded-tree-cache-misses>
</qm:fragment>
</qm:fragments>
<qm:documents>
<qm:document>
<qm:uri>new2.xml</qm:uri>
<qm:expanded-tree-cache-hits>1</qm:expanded-tree-cache-hits>
<qm:expanded-tree-cache-misses>0</qm:expanded-tree-cache-misses>
</qm:document>
<qm:document>
<qm:uri>new4.xml</qm:uri>
<qm:expanded-tree-cache-hits>1</qm:expanded-tree-cache-hits>
<qm:expanded-tree-cache-misses>0</qm:expanded-tree-cache-misses>
</qm:document>
<qm:document>
<qm:uri>new6.xml</qm:uri>
<qm:expanded-tree-cache-hits>1</qm:expanded-tree-cache-hits>
<qm:expanded-tree-cache-misses>0</qm:expanded-tree-cache-misses>
</qm:document>
<qm:document>
<qm:uri>new8.xml</qm:uri>
<qm:expanded-tree-cache-hits>1</qm:expanded-tree-cache-hits>
<qm:expanded-tree-cache-misses>0</qm:expanded-tree-cache-misses>
</qm:document>
</qm:documents>
</qm:query-meters>
We can see that the evaluator actually fetched 4 fragments from disk
while processing the results. It turns out there are over 10000
fragments in this query. To see that, we can look at the query-trace
results:
2007-06-14 15:51:41.546 Info: Docs: line 3:
xdmp:eval("xdmp:query-trace(true()), (for $t in
xdmp:document-properties()//prop:last-modified order by $t
descending return <node uri=""{base-uri
($t)}"">{xs:dateTime(data($t))}</node>)[1], xdmp:query-meters() ")
2007-06-14 15:51:41.546 Info: Docs: line 3: Analyzing path for $t:
xdmp:document-properties()/descendant::prop:last-modified
2007-06-14 15:51:41.546 Info: Docs: line 3: Step 1 is searchable:
xdmp:document-properties()
2007-06-14 15:51:41.548 Info: Docs: line 3: Step 2 is searchable:
descendant::prop:last-modified
2007-06-14 15:51:41.548 Info: Docs: line 3: Path is fully searchable.
2007-06-14 15:51:41.548 Info: Docs: line 3: Gathering constraints.
2007-06-14 15:51:41.548 Info: Docs: line 3: Step 2 test contributed 1
constraint: prop:last-modified
2007-06-14 15:51:41.548 Info: Docs: line 3: Order by clause
contributed 1 range ordering constraint for $t: order by $t descending
2007-06-14 15:51:41.548 Info: Docs: line 3: Executing search.
2007-06-14 15:51:41.708 Info: Docs: line 3: Selected 10040 fragments
to filter.
From the last line, you can see that index resolution found 10,040
candidate fragments for evaluating the program. But because it was
able to use a "range ordering constrain" (meaning it used the range
index) it was able to help the server avoid fetching all the fragments
off disk.
Why did we see more than one fragment in the query meters then?
That's because the server is doing some pre-fetching.
Cheers,
Ron
Ron Avnur
Lead Engineer
* Mark Logic Corporation*
2000 Alameda de las Pulgas
Suite 100
San Mateo, California 94403
+1 650 655 2319 Phone
+1 650 655 2310 Fax
[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
www.marklogic.com
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