Oracle XDB XML requires 10 times the space

Question

Issue:
Oracle XDB uses a lot of disk space. I persisted 10000 records of 24kb each.
Expected size = 24kb * 10000 = 235 MB
Actual size = 2.1G for XMLType table & 633M for CLOB table. Tablespace showed utilization of 91%.
Pls suggest ways to reduce disk usage ?
XMLTYPE table –
Structure = CREATE TABLE mytable OF XMLType XMLTYPE store AS SECUREFILE BINARY XML
Record size = 24kb ( xml measured as bytes )
Rows = 10000
Size of table space on file system (.dbf) = 2.1 GB
CLOB Table –
Structure = Create table mytable ( event CLOB)
Record size = 24kb ( xml measured as bytes )
Rows = 10000
Size of table space on file system (.dbf) = 633 MB
So a CLOB is about 2X and XMLType is 10X.
Is this expected? Can XMLType be tweeked to use less space?

Answer 1

The size of the datafile does not necessarily reflect the size of the object(s) within. How did you load the data? Did you perform any updates?
What is the value of bytes in user_segments for the table and the lob segment? How many extents have been allocated to each segment? Try running these queries before the data load against empty tables and then again after the load and note the diff in sizes.
select tablespace_name, segment_name, segment_type, blocks, bytes from user_segments order by tablespace_name, segment_name;
select * from user_extents order by tablespace_name, segment_name, extent_id;What are the attributes of the tablespaces that contain the table and lob segment? Extent sizes, extent allocation method?
select * from user_tablespaces;
select * from user_lobs;