Categories
dba sql

When v$session_longops is not long enough

With large table scans, sometimes the estimated total work is far beyond reality


SQL> select message from v$session_longops where target='SCOTT.EMP';

MESSAGE
------------------------------------------------------------
Table Scan: SCOTT.EMP: 7377612 out of 629683 Blocks done

The total work is the Oracle estimation :

SQL> select blocks from dba_tables where table_name='EMP';

BLOCKS
----------
629683

This may differ quite a lot from the segment size, for instance if the table is not very often analyzed :


SQL> select blocks, sysdate, last_analyzed from dba_tables where table_name='EMP';

BLOCKS SYSDATE LAST_ANALYZED
---------- ------------------- -------------------
629683 2013-04-21_09:21:47 2007-10-13_21:40:58

SQL> select blocks from dba_segments where segment_name='EMP';

BLOCKS
----------
7749888

I have customized my very long ops query to deal with very long waits.


col target for a20
set lin 150 pages 40000 termout off
alter session set nls_currency='%';
col PCT_DONE for 990.00L jus r
col time_remaining for 999999

select
lo.target,lo.sofar,seg.blocks,
lo.ELAPSED_SECONDS*seg.blocks/lo.sofar-lo.ELAPSED_SECONDS TIME_REMAINING,
100*lo.sofar/seg.blocks PCT_DONE
from
dba_segments seg,
v$session_longops lo
where
lo.units='Blocks'
and lo.totalwork>0 and (lo.time_remaining>0 or lo.time_remaining is null)
and regexp_substr(lo.target,'[^.]+') = seg.owner
and regexp_substr(lo.target,'[^.]+$') = seg.segment_name
/