XMLType's poor performance? (vs. Relational data retrieval)

Question

Hi,
I'm currently doing a proof of concept for the XMLType Vs Relational Storage.
I have TABLE_A which has the following DDL:
CREATE TABLE "WEBUSER"."TABLE_A"
( "HEADER_NUM" NUMBER(10,0),
"DETAIL_NUM" NUMBER(10,0),
"XML_RESPONSE" "SYS"."XMLTYPE"
) XMLTYPE COLUMN "XML_RESPONSE" STORE AS RELATIONAL XMLSCHEMA "MySchema.xsd" ELEMENT "test"
I have TABLE_B which has regular relational table structure (with each column representing a node in MySchema.xsd. The schema has around 85-100 elements.
Now I'm running queries as follows:
A) TO RETRIEVE XMLTYPE COLUMN
     StringBuilder queryStr = new StringBuilder();
     queryStr.append("SELECT X.* FROM TABLE_A X WHERE ROWNUM <= 10000 ORDER BY X.DETAIL_NUM");
     pstmt=conn.prepareStatement(queryStr.toString());     
     rs = pstmt.executeQuery();
     int totalRecordsFiltered = 0
     while(rs.next())
     totalRecordsFiltered++;
     System.out.println(totalRecordsFiltered);
B) TO RETRIEVE VALUES FROM RELATIONAL TABLE
     StringBuilder queryStr = new StringBuilder();
     queryStr.append("SELECT X.* FROM TABLE_B X WHERE ROWNUM <= 10000 ORDER BY X.DETAIL_NUM");
     pstmt=conn.prepareStatement(queryStr.toString());     
     rs = pstmt.executeQuery();
     int totalRecordsFiltered = 0
     while(rs.next())
     totalRecordsFiltered++;
     System.out.println(totalRecordsFiltered);
When the number of rows in both tables are 10,000
     - the While loop in (a) completes in about 5 min
     - the while loop in (b) completes in about 10 sec
Note that I'm really not doing anything inside the While loop. Just want to see how long it takes to loop through the resultset.
Can you please tell me why we see such difference in both types of data storage? Am I doing something wrong in the way resultset is handled?
I'm using Oracle 10g / ojdbc14.jar with JDBC thin driver / Websphere Application Server
Edited by: 916343 on Mar 7, 2012 1:03 PM
Edited by: 916343 on Mar 7, 2012 1:04 PM

Answer 1

First to answer you question..
1. There is no such option STORE AS RELATIOAL, I assume you meant OBJECT RELATIONAL.
2. We would need to see the XML schema, to get an idea of how complex the object model defined by the XML Schema is. We we would also need to see the instacne docuemnt to see how much of that model the instance document(s) are populating
3. Remember that your statement is going to retrieve all of the data ( which may require joining multliple tables to get all the content if the XML contains collections, we can't tell without seeing your schema) and then re-assemble the XML from the data stored in the object relational tables. This is way more expensive that simply fetching a number of columns from one table.
4. Note that in general if you are interested in fetching alll the XML, rather than fragments or scalar values the binary storage model (11g+) is a better choice for XML persistence. THe Object Relational model is more suited to situations where the access pattens on the XML willl be primarily leaf level selects and updates.
To answer Dan's comment...
If the you have an Ojbect Relational storage model, and write an XML Query using XMLTable to access leaf level nodes and the query is re-written in SQL it should be (nearly) as fast as a relational query for the same set of data. In some cases the XML can be faster since it alllows us to do master detail joins and only bring back the master data once for the result set, rather than once for each row in the result set.