Oracle 11g XMLType Experience - oracle

Question

1
Hello community,
we are currently evaluating possibilities to store generic data structures. We found that at least from a functional point of view Oracle XMLType is a good alternative to the good old BLOB. Because you can query and update single fields from the xml and also create indexes on XPath expressions.
We are a bit worried about the performance of XMLType. Especially the select performance in interesting. We have queries that select multiple data structures at once. These need to be fast.
Such a query looks something like this
SELECT DOC_VALUE.getClobval() AS XML_VALUE FROM XML_TABLE WHERE d.ID = IN ('1','2',...);
Our XML documents are 7 to 8 KB in size. We are on Oracle 11g and create the XML column with type 'XMLTYPE'
Do you have experience about the performance of selects on xml type columns. What overall experiences do you have with XMLTYPE. Is this a robust and fast Oracle feature? Or is it rather something immature and experimental.
Regards, Mathias

Answer 1

XMLDB is a strong and reliable feature we have since 9i.
Flexible-schema XMLType columns are implemented over hidden CLOB columns, while fixed-schema XMLType are decomposed into hidden tables and views; after all XMLType is as reliable as standard objects.
Performance would vary on your use, but just reading the whole XML on an XMLType is fast as reading the same on a classical CLOB, because actually it really just read and give you the XML code stored on CLOB as-is.

Answer 2

You can assign an XDB.XMLIndex to an XMLType, and performance will be good after that. We had a table with only 13,000 records, each containing an XML Clob that wasn't too big, maybe 40 pages each if it was printed on text, and running simple queries without an XMLIndex often took over 10 minutes, and running more complex queries often took 2x or 3x longer!
With an XMLIndex, the performance was on par with a typical table (On the order of milliseconds for full table scans). The XMLIndex can be as complex as you need it to be, I tried this naive one and it worked fine: (I say naive because I do not fully understand the inner workings of this index type!)
CREATE INDEX myschema.my_idx_name ON myschema.mytable
(SYS_MAKEXML(0,"SYS_SOMETHING$"))
INDEXTYPE IS XDB.XMLINDEX
NOPARALLEL;
You should understand the various XMLIndex options available to you, and choose according to your needs. Documentation:
https://docs.oracle.com/cd/B28359_01/appdev.111/b28369/xdb_indexing.htm#CHDJECDA