Weird explain plan on multi-level structured XmlType column

Question

Hello,
am running an explain on the follwing query on 11.2.0.2:
SELECT
T1.EVENT_ID,
ACTION_SUB_ID,
PARAM_KEY,
PARAM_VALUE,
TO_DATE('2013-12-10', 'YYYY-MM-DD')
FROM  T_C_RMP_MNTRNG_XML_FULL_IL ,
  XMLTABLE('/monitoring' PASSING XML_CONTENT COLUMNS
  EVENT_ID VARCHAR2(4000) PATH 'eventId',
  ACTIONS XMLTYPE PATH 'action'
) T1,
  XMLTABLE('/action' PASSING T1.ACTIONS COLUMNS
  ACTION_SUB_ID NUMBER(10,0) PATH 'actionSubId',
  PARAMS xmltype PATH 'param'
) T2,
  XMLTABLE('/param' PASSING T2.params columns
  PARAM_KEY VARCHAR2(4000) PATH 'key',
  PARAM_VALUE VARCHAR2(1000) PATH 'value'
) T3
WHERE MESSAGE_ID = 4972102 ;
Although MESSAGE_ID is the primary key of T_C_RMP_MNTRNG_XML_FULL_IL and thus there is only one record matching the condition, I get an explain plan with huge costs, 500MB of data and an estimated 10 hour runtime:
PLAN_TABLE_OUTPUT
Plan hash value: 4011854835
| Id  | Operation                      | Name                  | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT               |                       |   223K|   489M|  3111K  (1)| 10:22:17 |
|   1 |  NESTED LOOPS                  |                       |       |       |            |          |
|   2 |   NESTED LOOPS                 |                       |   223K|   489M|  3111K  (1)| 10:22:17 |
|   3 |    NESTED LOOPS                |                       |   140K|    11M|  1678   (1)| 00:00:21 |
|*  4 |     INDEX RANGE SCAN           | X1B                   |     1 |    53 |     3   (0)| 00:00:01 |
|   5 |     TABLE ACCESS BY INDEX ROWID| T_OR_MON_ACTION       |   140K|  4542K|  1675   (1)| 00:00:21 |
PLAN_TABLE_OUTPUT
|*  6 |      INDEX RANGE SCAN          | X3                    |   140K|       |     4  (25)| 00:00:01 |
|*  7 |    INDEX RANGE SCAN            | X4G                   |  4083 |       |    22   (0)| 00:00:01 |
|   8 |   TABLE ACCESS BY INDEX ROWID  | T_OR_MON_ACTION_PARAM |     2 |  4428 |    52   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   4 - access("MESSAGE_ID"=4972102)
   6 - access("SYS_ALIAS_0"."NESTED_TABLE_ID"="T_C_RMP_MNTRNG_XML_FULL_IL"."SYS_NC0001200013$")
   7 - access("NESTED_TABLE_ID"="SYS_ALIAS_0"."SYS_NC0000500006$")
PLAN_TABLE_OUTPUT
Note
   - dynamic sampling used for this statement (level=2)
When I run the query, the result comes back within 0.3 seconds.
Why is the explain plan off like that?
Is this just the way it is, or is there something going wrong here?

Answer 1

This is my table create statement:
CREATE TABLE QQRCSBI0.T_C_RMP_MNTRNG_XML_FULL_IL (
  MESSAGE_ID NUMBER(22,0) NOT NULL ENABLE,
  XML_EVAL_ID NUMBER(22,0),
  VIN7 VARCHAR2(7 BYTE),
  FLEET_ID VARCHAR2(50 BYTE),
  CSC_SW_VERSION VARCHAR2(100 BYTE),
  RECEIVED DATE,
  XML_CONTENT SYS.XMLTYPE ,
  DWH_LM_TS_UTC DATE NOT NULL ENABLE,
  CONSTRAINT PK_C_RMP_MNTRNG_XML_FULL_IL5 PRIMARY KEY (MESSAGE_ID)
) NOLOGGING TABLESPACE CATALOG
VARRAY "XML_CONTENT"."XMLDATA"."ACTION" STORE AS TABLE "T_OR_MON_ACTION" (
  NOLOGGING TABLESPACE "CATALOG"
  VARRAY "PARAM" STORE AS TABLE "T_OR_MON_ACTION_PARAM" (
  NOLOGGING TABLESPACE "CATALOG"
  ) RETURN AS LOCATOR
) RETURN AS LOCATOR
XMLTYPE XML_CONTENT STORE AS OBJECT RELATIONAL XMLSCHEMA "http://mydomain.com/csc_monitoring_session.xsd" ELEMENT "monitoring";
I set all default table names in the schema to blank and registered the schema with genTables=false.
I am still running into problems retrieving the 3rd level T_OR_MON_ACTION_PARAM data. The query just crashes after a while because it is running out of either TEMP space or UNDO space (it keeps changing). I'll take a step back to re-evaluate and post another thread about that in a bit I guess...
You said "SQL*Plus explain plan, goes most of the time bananas" - is there a difference in what client (SqlPlus or SqlDeveloper) I use to get the explain plan? I thought the plan was generated by the DB and the clients just display the result, and the only difference is the way the clients display the plan?!