UpdateXML query rewrite with unstructured data?

Question

Hi,
I'm currently loading unstructured, non-schema based XML and am trying to address some performance issues when I merge changes to a document.
I currently read the document from the table, merge the changes using XQuery and save the document back - however, I'm aware that this can be excessive when a minor number of changes are involved (I'm also seeing some contention on the path table when a number of parallel threads are involved).
I know that using "updateXML" and "insertChildXML" can be more efficient due to the XPath rewrite - however, I'm not sure if this is applicable when the XML is unstructured and non-schema based.
Any advice on this would be greatly appreciated.
Regards
Larry

Answer 1

Hi Larry,
I know that using "updateXML" and "insertChildXML" can be more efficient due to the XPath rewrite - however, I'm not sure if this is applicable when the XML is unstructured and non-schema based.XPath rewrite applies to structured (Object-Relational) storage, but to Binary XML and/or XMLIndex as well.
Besides, with Binary XML and a SECUREFILE LOB storage, a "sliding update" is used when the data is written back to disk (only the modified portion of the LOB is affected) thus reducing the overhead of writing whole documents over and over again even for small changes.
For example (OOX_SML_WORKBOOK is a binary XMLType table here) :
-- unstructured XMLIndex with path-subsetting :
CREATE INDEX oox_sml_workbook_uxi1 ON oox_sml_workbook (object_value) INDEXTYPE IS XDB.XMLIndex
  PARAMETERS ('PATH TABLE oox_sml_workbook_ptb
  PATHS (INCLUDE (/workbook/sheets/sheet)
                     NAMESPACE MAPPING (xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"))');
-- update of an attribute using updateXML function :
update oox_sml_workbook
set object_value = updateXML( object_value
                            , '/workbook/sheets/sheet[@sheetId="3"]/@name'
                            , 'NewName'
                            , 'xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"' )
where xmlexists('declare default element namespace "http://schemas.openxmlformats.org/spreadsheetml/2006/main"; (::)
                 /workbook/sheets/sheet[@sheetId="3"]'
                passing object_value)
;If you're lucky and currently working with the latest patchset (11.2.0.3), you can also use XQuery Update Facility, a small extension to the XQuery standard that allows various kinds of operations on nodes : inserting (after/before), updating, renaming and deleting.
This extension supersedes the old proprietary functions updateXML, insertXML etc.
And it can be optimized via XPath/XQuery rewrite too :
update oox_sml_workbook
set object_value =
    xmlquery('declare default element namespace "http://schemas.openxmlformats.org/spreadsheetml/2006/main"; (::)
              copy $d := .
              modify (
                for $i in $d/workbook/sheets/sheet
                return replace value of node $i/@name with concat("MySheet",$i/@sheetId)
              return $d'
              passing object_value
              returning content)
;