Native SQL query - Need help

Question

Hi All,
We have a native SQL query accessing Oracle database(given below).
Can anyone please let me know what this query is about and how can we fine tune the query?
SELECT O.OBJECT_NAME ,
               H.SID,
               HS.MACHINE,
               HS.PROCESS,
               W.SID,
               WS.MACHINE,
               WS.PROCESS,
               H.CTIME,
               W.CTIME,
               WS.ROW_WAIT_OBJ#,
               WS.ROW_WAIT_FILE#,
               WS.ROW_WAIT_BLOCK#,
               WS.ROW_WAIT_ROW#,
               HP.SPID,
               WP.SPID
        FROM V$LOCK H, V$LOCK W, V$LOCK I, V$LOCK I2, ALL_OBJECTS O,
             V$SESSION HS, V$SESSION WS, V$PROCESS HP, V$PROCESS WP
        WHERE   H.ID1 = W.ID1
        AND     H.SID <> W.SID
        AND     H.TYPE IN ('TX','DL')
        AND     H.REQUEST = 0
        AND     H.SID = I.SID
        AND     I.TYPE = 'TM'
        AND     I.ID1 = O.OBJECT_ID
        AND     I.ID1 = I2.ID1
        AND     W.SID = I2.SID
        AND     I2.TYPE = 'TM'
        AND     H.SID = HS.SID
        AND     W.SID = WS.SID
        AND     HS.PADDR = HP.ADDR
        AND     WS.PADDR = WP.ADDR
        INTO :EXCL_LOCK_WAITERS-OBJ_NAME   ,
             :EXCL_LOCK_WAITERS-HOLDER_SID ,
             :EXCL_LOCK_WAITERS-H_HOSTNAME ,
            :EXCL_LOCK_WAITERS-HOLDER_PID ,
             :HOLDER_PID ,
             :EXCL_LOCK_WAITERS-WAITER_SID ,
             :EXCL_LOCK_WAITERS-W_HOSTNAME ,
            :EXCL_LOCK_WAITERS-WAITER_PID ,
             :WAITER_PID ,
             :EXCL_LOCK_WAITERS-HELD_SINCE ,
             :EXCL_LOCK_WAITERS-WAITSSINCE,
             :ROW_WAIT_OBJ,
             :ROW_WAIT_FILE,
             :ROW_WAIT_BLOCK,
             :ROW_WAIT_ROW,
             :H_PROCESS,
             :W_PROCESS
      ENDEXEC
Thanks in advance.
Neethu Mohan

Answer 1

Hi Neethu,
It gives you an overwiew of blocking Oracle sessions.
1. In general, the SQL checks Oracle sessions (SID's) that were requirering a DML lock ('TM') and now holding row locks (TX)  to prevent destructive interference of simultaneous conflicting DML or DDL operations. DML statements automatically acquire both table-level locks and row-level locks ('TX')  => holders
It joins these with the sessions that are waiting of releasing the lock by the holders  => waiters.
2. it retrieves the detail information wich  Oracle process , the object (table) , it's row , block  and file
are affected by the locks.
3. Normally, the locks are only hold for a short period of time. If you have blocking sessions it may be of a log running task (i.e. mass data update of a table) ; but it could also be a application bug due to improper handling of concurrent updates of the same object.
4. Tuning
V$tables are expensive to query: Why?
v$ tables are generally Oracle memory structures.
v$ tables are not read consistent.
v$ tables require latches to access -- cannot modify and read memory at the same
time.
heavy access to v$ tables like this may cause some serious heavy duty contention.
Especially if you self join V$lock several times.
So the best would be to save the contents of V$LOCK in some table:
Create table mylocks as select * from v$lock;
Use that table for self-joining and joins to the other tables.
You can also CTAS the other v$ tables to bypass the performance bottleneck while retrieving
v$ directly.
You can empty or drop the created tables any time for new data.
Because you want to investigate only lock hold for a longert time  to copy the v$ memory structures into
physical tables is not a disadvantage. You certainly will wait longer on finishing your query
instead of copy them into the tables.
Hope this helped
yk