How to know the usage of temporary tablespace in Oracle

Question

I am trying to compare two tables which are very large in my system(Oracle 10g). The way I used to compare is the "MINUS" operation. Because of the large size of tables, I want to know the usage of the temporary tablespace on the real time.

I googled someways on how to get the usage of the tempory tablespace. But I am not sure which one is right.Here are the three ways:

1.select TABLESPACE_NAME, BYTES_USED, BYTES_FREE from V$TEMP_SPACE_HEADER;

2.select BYTES_USED,BYTES_CACHED from V$TEMP_EXTEND_POOL

   What is the difference of BYTES_USED and BYTES_CACHED

3.select USED_EXTENDS, USED_BLOCKS v$sort_segment

the three ways really confused me a lot and I don't know what is the difference.

Answer 1

Look at the dynamic perfomance views v$sql_workarea and v$sql_workarea_active -- they will tell you not only how much space is being used by the query, but how much of it is attributable to different phases in the execution plan, what sort of sort area it is (hash join etc) and how it is being used (one-pass etc). It'll be a much more effective method of performance tuning.

Answer 2

V$SORT_SEGMENT view can be used to get used/free extents, used/free blocks information for TEMPORARY tablespaces.

V$TEMP_SPACE_HEADER and V$TEMP_EXTEND_POOL views are almost the same which provides used bytes information. However, V$TEMP_EXTEND_POOL is reliable because former is updated only when DB is restarted or tablespace is recreated.

Note: From Oracle 11g, DBA_TEMP_FREE_SPACE view can be used to get TEMPORARY tablespace information.