Application Looping Until Lock a Row with NOWAIT Clause


GREPORA

Yesterday I treated an interesting situation:
A BATCH stayed on “SQL*Net message from client” event but the last_call_et was always on 1 or 0. Seems OK, with some client contention to send the commands to the DBMS, right? Nope.

It was caused by a loop in the application code “waiting” for a row lock but without “DBMS waiting events” (something like “select * from table for update nowait”). Take a look in how it was identified below.

First the session with no SQL_ID, no wait events and last_Call_et=0 of a “BATH_PROCESS” user:

proddb2> @sid
Sid:9796
Inst:
LAST_CALL_ET SQL_ID   EVENT STATUS SID SERIAL# INST_ID USERNAME
------------ ------- ------------- ---------- ------------------------
0 SQL*Net message from client INACTIVE 9796 45117 2 BATCH_PROCESS
proddb2> @trace
Enter value for sid: 9796
Enter value for serial: 45117
PL/SQL procedure successfully completed.

As you see, with no idea about what is happening, I started a trace. The…

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