Databases Reference
In-Depth Information
In the previous screenshot we can see the
SID
, identifying the session, and which session is
locking (
BLOCK=1
) other sessions. In our example, session
31
(our
SESSION
1
) is blocking
session
17
(our
SESSION
2
).
The
TYPE
field indicates that two different types of locks are held by session
31
: a
TM
, or Table
Level Lock. This prevents DDL operations on the object with
ID
74136
, and a
TX
, or Row Level
Lock, which ensures that at the same time no two transactions modify the same row.
In the previous screenshot we can also see the result for the query in step 7, which tells us
that the object on which the
TM
lock is held is the
SH.CUSTOMERS
table.
In step 8 we query the
V$LOCKED_OBJECT
dynamic performance view, obtaining the
following results:
Using this view we can see the undo segment number (XIDUSN), the slot number (XIDSLOT),
and the sequence number (XIDSQN) by the session specified. The view also shows the object
ID, the username (
SH
in our example), and other information about the locks acquired in
the system.
