Another index question
Monday, 18 January 2010 · 1 message
CG
Christian Grün18 Jan 2010 20:44 #
Hi Phil,
in nearly all cases, the query optimizer will try to apply the existing index structures. As the XQuery syntax is much more versatile than SQL, this won't always succeed. - However, your query can be easily written. Three alternative writings, that all should access the index, look as follows:
Query:
//page[para[text() contains text "indiana"]
and para[text() contains text "ninth"]]
Alternative 1:
//page[para/text() contains text "indiana"]
[para/text() contains text "ninth"]
Alternative 2:
//page[para/text() contains text "indiana" and
para/text() contains text "ninth"]
Alternative 3:
//page[para/text() contains text "indiana" ftand "ninth"]
All three queries will yield different execution plans, and - to be strict - the third plan is not equivalent to the first two, as it expects the two query terms to occur in the very same text node. - Check out all of the alternatives to see which one works out best for you.
Christian
Quoted text · Phil Oliver · 26 lines
On Mon, Jan 18, 2010 at 7:25 PM, Phil Oliver <phil3 at olivercomputing.com> wrote: > Another question regarding usage of full-text indices. My test database has > the full text indexing enabled with no options currently for simplicity > (e.g. wildcards, stemming, etc. disabled). > > A simple query such as: > > let $p:=//para[text() contains text "indiana"] > return $p > > executes rapidly using the FT index selection. However, if I try a more > complex query (designed to find two words on the same page): > > let $p:=//page[para[text() contains text "indiana"] and para[text() contains > text "ninth"]] > return $p > > the query plan does *not* use the FT index and takes a long time to execute. > > While this is a more complex query, it doesn't seem *really* complex, and > would be a common use case. Can you give me some idea as to why the FT > indices are not used in this instance, and if possible a suggestion on a > rewritten query that would use them? Is there a way to give hints to the > optimizer to always use them? > >
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