2-cpu, 220mhz, 32-bit HPUX 11.0. Oracle 8.1.7.0.0
Could someone explain what's going on here?
This SQL takes no time at all :
select
substr(username , 1, 12) "User"
, substr(lock_type, 1, 18) "Lock Type"
, substr(mode_held, 1, 18) "Mode Held"
from sys.dba_lock a
, v$session b
where /*lock_type not in ('Media Recovery','Redo Thread')
and*/ a.session_id = b.sid;
with explain plan:
SELECT STATEMENT Optimizer=CHOOSE (Cost=70 Card=1 Bytes=148)
NESTED LOOPS (Cost=70 Card=1 Bytes=148)
NESTED LOOPS (Cost=60 Card=1 Bytes=141)
NESTED LOOPS (Cost=20 Card=1 Bytes=107)
FIXED TABLE (FULL) OF X$KSUSE (Cost=10 Card=1 Bytes=30)
FIXED TABLE (FIXED INDEX #1) OF X$KSUSE (Cost=10 Card=1
Bytes=77)
VIEW OF GV$_LOCK
UNION-ALL
VIEW OF GV$_LOCK1 (Cost=20 Card=2 Bytes=162)
UNION-ALL
FIXED TABLE (FULL) OF X$KDNSSF (Cost=10 Card=1
Bytes=94)
FIXED TABLE (FULL) OF X$KSQEQ (Cost=10 Card=1
Bytes=94)
FIXED TABLE (FULL) OF X$KTADM (Cost=10 Card=1 Bytes=94)
FIXED TABLE (FULL) OF X$KTCXB (Cost=10 Card=1 Bytes=94)
FIXED TABLE (FIXED INDEX #1) OF X$KSQRS (Cost=10 Card=100
Bytes=700)
whereas an uncommented predicate consumes 40 minutes of CPU (sez TOP) with
this explain plan:
SELECT STATEMENT Optimizer=CHOOSE (Cost=70 Card=1 Bytes=148)
NESTED LOOPS (Cost=70 Card=1 Bytes=148)
NESTED LOOPS (Cost=30 Card=1 Bytes=114)
MERGE JOIN (CARTESIAN) (Cost=20 Card=1 Bytes=37)
FIXED TABLE (FULL) OF X$KSUSE (Cost=10 Card=1 Bytes=30)
SORT (JOIN) (Cost=10 Card=1 Bytes=7)
FIXED TABLE (FULL) OF X$KSQRS (Cost=10 Card=1 Bytes=7)
FIXED TABLE (FIXED INDEX #1) OF X$KSUSE (Cost=10 Card=1
Bytes=77)
VIEW OF GV$_LOCK
UNION-ALL
VIEW OF GV$_LOCK1 (Cost=20 Card=2 Bytes=162)
UNION-ALL
FIXED TABLE (FULL) OF X$KDNSSF (Cost=10 Card=1 Bytes=94)
FIXED TABLE (FULL) OF X$KSQEQ (Cost=10 Card=1 Bytes=94)
FIXED TABLE (FULL) OF X$KTADM (Cost=10 Card=1 Bytes=94)
FIXED TABLE (FULL) OF X$KTCXB (Cost=10 Card=1 Bytes=94)
If it jams, force it. If it breaks, it needed replacing anyway. --John F
Duval
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