Why Isn't xmlindex being used in slow query on binary xml table eval?

Question

I am running a slow simple query on Oracle database server 11.2.0.1 that is not using an xmlindex. Instead, a full table scan against the eval binary xml table occurs. Here is the query:
select -- /*+ NO_XMLINDEX_REWRITE no_parallel(eval)*/
      defid from eval,
      XMLTable(XMLNAMESPACES(DEFAULT 'http://www.cigna.com/acme/domains/eval/2010/03',
      'http://www.cigna.com/acme/domains/derived/fact/2010/03' AS "ns7"),
      '$doc/eval/derivedFacts/ns7:derivedFact' passing eval.object_value as "doc" columns defid varchar2(100) path 'ns7:defId'
       ) eval_xml
where eval_xml.defid in ('59543','55208'); The predicate is not selective at all - the returned row count is the same as the table row count (325,550 xml documents in the eval table). When different values are used bringing the row count down to ~ 33%, the xmlindex still isn't used - as would be expected in a purely relational nonXML environment.
My question is why would'nt the xmlindex be used in a fast full scan manner versus a full table scan traversing the xml in each eval table document record?
Would a FFS hint be applicable to an xmlindex domain-type index?
Here is the xmlindex definition:
CREATE INDEX "EVAL_XMLINDEX_IX" ON "EVAL" (OBJECT_VALUE)
  INDEXTYPE IS "XDB"."XMLINDEX" PARAMETERS
  ('XMLTable eval_idx_tab XMLNamespaces(DEFAULT ''http://www.cigna.com/acme/domains/eval/2010/03'',
  ''http://www.cigna.com/acme/domains/derived/fact/2010/03'' AS "ns7"),''/eval''
       COLUMNS defId VARCHAR2(100) path ''/derivedFacts/ns7:derivedFact/ns7:defId''');Here is the eval table definition:
CREATE
  TABLE "N98991"."EVAL" OF XMLTYPE
    CONSTRAINT "EVAL_ID_PK" PRIMARY KEY ("EVAL_ID") USING INDEX PCTFREE 10
    INITRANS 4 MAXTRANS 255 COMPUTE STATISTICS STORAGE(INITIAL 65536 NEXT
    1048576 MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 FREELISTS 1
    FREELIST GROUPS 1 BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE
    DEFAULT) TABLESPACE "ACME_DATA" ENABLE
  XMLTYPE STORE AS SECUREFILE BINARY XML
    TABLESPACE "ACME_DATA" ENABLE STORAGE IN ROW CHUNK 8192 CACHE NOCOMPRESS
    KEEP_DUPLICATES STORAGE(INITIAL 106496 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS
    2147483645 PCTINCREASE 0 BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT
    CELL_FLASH_CACHE DEFAULT)
  ALLOW NONSCHEMA ALLOW ANYSCHEMA VIRTUAL COLUMNS
    "EVAL_DT" AS (SYS_EXTRACT_UTC(CAST(TO_TIMESTAMP_TZ(SYS_XQ_UPKXML2SQL(
    SYS_XQEXVAL(XMLQUERY(
    'declare default element namespace "http://www.cigna.com/acme/domains/eval/2010/03"; (::)
/eval/@eval_dt'
    PASSING BY VALUE SYS_MAKEXML(128,"XMLDATA") RETURNING CONTENT ),0,0,
    16777216,0),50,1,2),'SYYYY-MM-DD"T"HH24:MI:SS.FFTZH:TZM') AS TIMESTAMP
WITH
  TIME ZONE))),
    "EVAL_CAT" AS (CAST(SYS_XQ_UPKXML2SQL(SYS_XQEXVAL(XMLQUERY(
    'declare default element namespace "http://www.cigna.com/acme/domains/eval/2010/03";/eval/@category'
    PASSING BY VALUE SYS_MAKEXML(128,"XMLDATA") RETURNING CONTENT ),0,0,
    16777216,0),50,1,2) AS VARCHAR2(50))),
    "ACME_MBR_ID" AS (CAST(SYS_XQ_UPKXML2SQL(SYS_XQEXVAL(XMLQUERY(
    'declare default element namespace "http://www.cigna.com/acme/domains/eval/2010/03";/eval/@acmeMemberId'
    PASSING BY VALUE SYS_MAKEXML(128,"XMLDATA") RETURNING CONTENT ),0,0,
    16777216,0),50,1,2) AS VARCHAR2(50))),
    "EVAL_ID" AS (CAST(SYS_XQ_UPKXML2SQL(SYS_XQEXVAL(XMLQUERY(
    'declare default element namespace "http://www.cigna.com/acme/domains/eval/2010/03";/eval/@evalId'
    PASSING BY VALUE SYS_MAKEXML(128,"XMLDATA") RETURNING CONTENT ),0,0,
    16777216,0),50,1,2) AS VARCHAR2(50)))
  PCTFREE 0 PCTUSED 80 INITRANS 4 MAXTRANS 255 NOCOMPRESS LOGGING STORAGE
    INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0
    FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT
    CELL_FLASH_CACHE DEFAULT
  TABLESPACE "ACME_DATA" ; Sample cleansed xml snippet:
<?xml version = '1.0' encoding = 'UTF-8' standalone = 'yes'?><eval createdById="xxxx" hhhhMemberId="37e6f05a-88dc-41e9-a8df-2a2ac6d822c9" category="eeeeeeee" eval_dt="2012-02-11T23:47:02.645Z" evalId="12e007f5-b7c3-4da2-b8b8-4bf066675d1a" xmlns="http://www.xxxxx.com/vvvv/domains/eval/2010/03" xmlns:ns2="http://www.cigna.com/nnnn/domains/derived/fact/2010/03" xmlns:ns3="http://www.xxxxx.com/vvvv/domains/common/2010/03">
   <derivedFacts>
      <ns2:derivedFact>
         <ns2:defId>12345</ns2:defId>
         <ns2:defUrn>urn:mmmmrunner:Medical:Definition:DerivedFact:52657:1</ns2:defUrn>
         <ns2:factSource>tttt Member</ns2:factSource>
         <ns2:origInferred_dt>2012-02-11T23:47:02.645Z</ns2:origInferred_dt>
         <ns2:factValue>
            <ns2:type>boolean</ns2:type>
            <ns2:value>true</ns2:value>
         </ns2:factValue>
      </ns2:derivedFact>
      <ns2:derivedFact>
         <ns2:defId>52600</ns2:defId>
         <ns2:defUrn>urn:ddddrunner:Medical:Definition:DerivedFact:52600:2</ns2:defUrn>
         <ns2:factSource>cccc Member</ns2:factSource>
         <ns2:origInferred_dt>2012-02-11T23:47:02.645Z</ns2:origInferred_dt>
         <ns2:factValue>
            <ns2:type>string</ns2:type>
            <ns2:value>null</ns2:value>
         </ns2:factValue>
      </ns2:derivedFact>
      <ns2:derivedFact>
         <ns2:defId>59543</ns2:defId>
         <ns2:defUrn>urn:ddddunner:Medical:Definition:DerivedFact:52599:1</ns2:defUrn>
         <ns2:factSource>dddd Member</ns2:factSource>
         <ns2:origInferred_dt>2012-02-11T23:47:02.645Z</ns2:origInferred_dt>
         <ns2:factValue>
            <ns2:type>string</ns2:type>
            <ns2:value>INT</ns2:value>
         </ns2:factValue>
      </ns2:derivedFact>
            With the repeating <ns2:derivedFact> element continuing under the <derivedFacts>The Oracle XML DB Developer's Guide 11g Release 2 isn't helping much...
Any assitance much appreciated.
Regards,
Rick Blanchard

Answer 1

odie 63, et. al.;
Attached is the reworked select query, xmlindex, and 2ndary indexes. Note: though namespaces are used; we're not registering any schema defns.
SELECT /*+ NO_USE_HASH(eval) +/ --/*+ NO_QUERY_REWRITE no_parallel(eval)*/
eval_xml.eval_catt, df.defid FROM eval,
--df.defid FROM eval,
XMLTable(XMLNamespaces( DEFAULT 'http://www.cigna.com/acme/domains/eval/2010/03',
                        'http://www.cigna.com/acme/domains/derived/fact/2010/03' AS "ns7" ),
        '/eval' passing eval.object_value
         COLUMNS
           eval_catt VARCHAR2(50) path '@category',
           derivedFact XMLTYPE path '/derivedFacts/ns7:derivedFact')eval_xml,
XMLTable(XMLNamespaces('http://www.cigna.com/acme/domains/derived/fact/2010/03' AS "ns7",
                          DEFAULT 'http://www.cigna.com/acme/domains/eval/2010/03'),
        '/ns7:derivedFact' passing eval_xml.derivedFact
         COLUMNS
           defid VARCHAR2(100) path 'ns7:defId') df
WHERE df.defid IN ('52657','52599') AND eval_xml.eval_catt LIKE 'external';
--where df.defid = '52657';
SELECT /*+ NO_USE_HASH(eval +/ --/*+ NO_QUERY_REWRITE no_parallel(eval)*/
eval_xml.eval_catt, df.defid FROM eval,
--df.defid FROM eval,
XMLTable(XMLNamespaces( DEFAULT 'http://www.cigna.com/acme/domains/eval/2010/03',
                        'http://www.cigna.com/acme/domains/derived/fact/2010/03' AS "ns7" ),
        '/eval' passing eval.object_value
         COLUMNS
           eval_catt VARCHAR2(50) path '@category',
           derivedFact XMLTYPE path '/derivedFacts/ns7:derivedFact')eval_xml,
XMLTable(XMLNamespaces('http://www.cigna.com/acme/domains/derived/fact/2010/03' AS "ns7",
                          DEFAULT 'http://www.cigna.com/acme/domains/eval/2010/03'),
        '/ns7:derivedFact' passing eval_xml.derivedFact
         COLUMNS
           defid VARCHAR2(100) path 'ns7:defId') df
WHERE df.defid IN ('52657','52599') AND eval_xml.eval_catt LIKE 'external';
--where df.defid = '52657'; create index defid_2ndary_ix on eval_idx_tab_II (defID);
     eval_catt VARCHAR2(50) path ''@CATEGORY''');
create index eval_catt_2ndary_ix on eval_idx_tab_I (eval_catt);The xmlindex is getting picked up but a couple of problesm:
1. In the developemnt environment, no xml source records for defid '52657' or '52599' are being displayed - just an empty output set occurs; in spite of these values being present and stored in the source xml.
This really has me stumped, as can query the eval table to see the actual xml defid vaues '52657' and '52599' exist. Something appears off with the query - which didn't return records even before the corrresponding xml index was created.
2. The query still performs slowly, in spite of using the xmlindex. The execution plan shows a full table scan of eval occurring whether or not a HASH JOIN or MERGE JOIN (gets used in place of the HASH JOIN when the NO_USE_HASH(eval) int is used.
3. Single column 2ndary indexes created respectively for eval_catt and defid are not used in the execution plan - which may be expected upon further consideration.
In the process of running stats at this moment, to see if performance improves....
At this point, really after why item '1.' is occurring?
Edited by: RickBlanchardSRSCigna on Apr 16, 2012 1:33 PM