Query on virtual column that is defined in XMLIndex does not use the index

Question

Hello,
I am facing an issue in executing queries on a virtual column that is defined in an XMLIndex: it appears as if the index is not used.
Database details:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
PL/SQL Release 11.2.0.3.0 - Production
CORE 11.2.0.3.0 Production
TNS for 64-bit Windows: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production
For this use case the XML documents adhere to the following XSD and are stored in an XMLType column in a table:
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns="http://a_name_space/v1"
    targetNamespace="http://a_name_space/v1"
    elementFormDefault="qualified" attributeFormDefault="unqualified" version="1.0">
    <xsd:element name="fields">
        <xsd:complexType>
            <xsd:sequence>
                <xsd:element name="field" maxOccurs="unbounded">
                    <xsd:complexType>
                        <xsd:choice>
                            <xsd:element name="value" minOccurs="1" maxOccurs="1">
                                <xsd:complexType>
                                    <xsd:simpleContent>
                                        <xsd:extension base="notEmptyString4000Type"/>
                                    </xsd:simpleContent>
                                </xsd:complexType>
                            </xsd:element>
                            <xsd:element name="values" minOccurs="1" maxOccurs="1">
                                <xsd:complexType>
                                    <xsd:sequence>
                                        <xsd:element name="value" minOccurs="1" maxOccurs="1">
                                            <xsd:complexType>
                                                <xsd:simpleContent>
                                                    <xsd:extension base="notEmptyString4000Type">
                                                        <xsd:attribute name="startDate" type="xsd:date" use="required"/>
                                                        <xsd:attribute name="endDate" type="xsd:date" />
                                                    </xsd:extension>
                                                </xsd:simpleContent>
                                            </xsd:complexType>
                                        </xsd:element>
                                    </xsd:sequence>
                                </xsd:complexType>
                            </xsd:element>
                        </xsd:choice>
                        <xsd:attribute name="name" type="string30Type" use="required"/>
                        <xsd:attribute name="type" type="dataType" use="required"/>
                    </xsd:complexType>
                </xsd:element>
            </xsd:sequence>
        </xsd:complexType>
    </xsd:element>
    <xsd:simpleType name="dataType">
        <xsd:annotation>
            <xsd:documentation>Char, Date, Number</xsd:documentation>
        </xsd:annotation>
        <xsd:restriction base="xsd:string">
            <xsd:enumeration value="C"/>
            <xsd:enumeration value="D"/>
            <xsd:enumeration value="N"/>
        </xsd:restriction>
    </xsd:simpleType>
    <xsd:simpleType name="string30Type">
        <xsd:restriction base="xsd:string">
            <xsd:maxLength value="30"/>
        </xsd:restriction>
    </xsd:simpleType>
    <xsd:simpleType name="notEmptyString4000Type">
        <xsd:restriction base="xsd:string">
            <xsd:maxLength value="4000"/>
            <xsd:pattern value=".+"/>
        </xsd:restriction>
    </xsd:simpleType>
</xsd:schema>A field can have a single value as well as multiple values.
The XMLIndex is defined as follows:
CREATE INDEX test_xmltype_idx ON test_xmltype (additional_fields) INDEXTYPE IS XDB.XMLIndex
PARAMETERS
XMLTable dt_fld_tab (TABLESPACE "TAB_SPACE" COMPRESS FOR OLTP) ''fields/field''
COLUMNS
name varchar2(30 char) PATH ''@name''
,dataType varchar2(1 char) PATH ''@type''
,val varchar2(4000 char) PATH ''value/text()''
,vals XMLType PATH ''values/value'' VIRTUAL
XMLTable dt_fld_multi_value_tab (TABLESPACE "TAB_SPACE" COMPRESS FOR OLTP) ''value'' passing vals
COLUMNS
val varchar2(4000) PATH ''text()''
,startDate varchar2(30 char) PATH ''@startDate''
,endDate varchar2(30 char) PATH ''@endDate''
');The following b-tree indexes are defined:
create index dt_field_name_idx on dt_fld_tab (name);
create index dt_field_value_idx on dt_fld_tab (val);
create index dt_field_values_idx on dt_fld_multi_value_tab (val);And stats are properly computed before the queries are executed:
call dbms_stats.gather_table_stats(user, 'test_xmltype', estimate_percent => null);Queries for single values are cost efficient and fast. With 600K rows in the table these return with 0.002 seconds.
Queries for multi-valued fields / elements are not though, these result in a full table scan.
Sample XML snippet:
<fields>
  <field name="multiVal" type="C">
    <values>
      <value startDate="2013-01-01" endDate="2013-01-01">100</value>
      <value startDate="2014-01-01">120</value>
    </values>
  </field>
</fields>Examples of costly and slow queries:
select id from test_xmltype
where xmlexists('/fields/field/@name="multiVal"' passing additional_fields)
and xmlexists('/fields/field/values/value[@startDate="2013-01-01"]' passing additional_fields)
and xmlexists('/fields/field/values/value[text()="100"]' passing additional_fields)
select id from test_xmltype
where xmlexists('/fields/field/@name="multiVal"' passing additional_fields)
and xmlexists('/fields/field/values/value[@startDate="2013-01-01" and .="100"]' passing additional_fields);Whereas the following query on the multi valued field is fast:
select id from test_xmltype
where xmlexists('/fields/field/@name="multiVal"' passing additional_fields)
and xmlexists('/fields/field/values/value[@startDate="2013-01-01"]' passing additional_fields);For the XPath /fields/field/values/value[@startDate="2013-01-01"] the index is used.
Suspected cause: XPath issue for the value of a multi valued field, e.g. /fields/field/values/value[text()="aValue"].
Any hints are appreciated: what am I overlooking here?
Thanks in advance,
-Sjoerd
Edited by: user615230 on May 27, 2013 7:46 AM

Answer 1

Hello,
This is using binary XML. The table creation script is:
create table test_xmltype
(id number(14,0) not null primary key
,member_code varchar2(30 char) not null
,period_code varchar2(30 char) not null
,amount number(12,2) not null
,additional_fields xmltype
);The schema is not registered in the database. Is that required? It is primarily used to generate Java classes that will be used in order to construct the XML documents.
And you are right: for our initial investigation the sample XML documents are generated with a PLSQL routine and do not contain namespaces. But for the single valued fields there are also no namespaces and the queries on these are executed with very satisfactory plans.
Thanks for the swift reply.
-Sjoerd