Answer / jiwitesh

RMAN makes up to five attempts to get the enqueue and then
fails the job. The conflict is usually caused when two jobs
are both backing up the control file, and the job that
first starts backing up the control file waits for service
from the media manager.

Solution Commonly, enqueue situations occur when a job is
writing to a tape drive, but the tape drive is waiting for
new tape to be inserted. If you start a new job in this
situation, then you will probably receive the enqueue
message because the first job cannot complete until the new
tape is loaded.

Kill all the hanging session or wait to finish the seeion
and then retry.

Answer / gaurav ojha

When Recovery Manager (RMAN) needs to back up or
resynchronize from the control file, it first creates a
snapshot or consistent image of the control file. If one
RMAN job is already backing up the control file, while
another needs to create a new snapshot control file, then
the following message may show up:

RMAN-08512: waiting for snapshot controlfile enqueue

To determine which job is holding the conflicting enqueue,
do the following:
After the first RMAN-08512 message appears, start a new
SQL*Plus session on the target database as shown:


% sqlplus sys/sys_pwd@prod1


Execute the following query to determine which job is
causing the wait:


SELECT s.sid, username AS "User", program, module, action,
logon_time "Logon", l.*
FROM v$session s, v$enqueue_lock l
WHERE l.sid = s.sid and l.type = 'CF' AND l.id1 = 0 and
l.id2 = 2;

The output shown should be similar to the following (the
output in this example has been truncated):

SID User Program Module Action Logon
--- ---- -------------------- -------------------------
---------------- ---------
9 SYS rman@h13 (TNS V1-V3) backup full datafile: c1 0000210


Solution:

After determining which job is creating the enqueue, do one
of the following:

1. Wait until the job creating the enqueue completes

OR

2. Cancel the current job and restart it once the job
creating the enqueue completes

Answer / guest

Cause: The attempted operation cannot be executed at this
time because another process currently holds the snapshot
controlfile enqueue.

Action: Retry the operation after the concurrent operation
that is holding the snapshot controlfile enqueue terminates.

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