Block Change Tracking and Duplicate: avoid ORA-19755

If you use Block Change Tracking on your production database and try to duplicate it, you there are good possibilities that you will encounter this error:

ORA-19755: could not open change tracking file
ORA-19750: change tracking file: ‘/u02/oradata/ORCL/ORCL_bct.dbf’
ORA-27037: unable to obtain file status

The problem is caused by the block change tracking file entry that exists in the target controlfile, but Oracle can’t find the file because the directory structure on the auxiliary server changes.

After the restore and recovery of the auxiliary database, the duplicate process tries to open the DB but the bct file doesn’t exist and the error is thrown.

If you do a quick google search you will find several workarounds:

• disable the block change tracking after you get the error and manually open the auxiliary instance (this prevent the possibility to get the duplicate outcome from the rman return code)
• disable the BCT on the target before running the duplicate (this forces your incremental backups to read all your target database!)
• Richard Harrison proposed another workaround, you can read more about it here.

There is another workaround that I like more (and that you can also find as comment in Richard’s post):

• Disable the Block Change Tracking on the auxiliary while it’s doing the restore/recovery (in mounted status)

(This solutions isn’t coming from me, but as far as I know, the father of this solution is a colleague working at Trivadis.)

You can easily fork a process before running the duplicate command that:

• loops and checks the auxiliary instance status
• run the disable as soon as the auxiliary is mounted

I’ve worked out this script that does the job:

#!/bin/ksh

if [ $# -ne 1 ] ; then
        echo "Usage: $0 \$ORACLE_SID"
        exit 1
fi
ORACLE_SID=$1
export ORACLE_SID

ORACLE_HOME=`cat /etc/oratab | grep ^$ORACLE_SID | awk -F":" '{print $2}'`
export ORACLE_HOME


disable_trk () {
        echo "DISABLE BLOCK CHANGE TRACKING"
        sqlplus -s / as sysdba << EOF
        set echo on
        col FILENAME for a30
        ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;
        select * from v\$block_change_tracking;
EOF
}

echo "Checking block change tracking for $ORACLE_SID"

PATH=${ORACLE_HOME}/bin:$PATH; export PATH

## for how much time do you want to run the check?
INTERVAL=30
MAXCOUNT=30

# loop until the database status is either MOUNTED or OPEN
COUNT=1
while [ $COUNT -le $MAXCOUNT ] ; do
        STATUS=`sqlplus -s / as sysdba <<EOF
                whenever sqlerror exit SQL.SQLCODE;
                set head off feed off
                select status from v\\$instance;
EOF
`
        if [ $? -eq 0 ] ; then
                if [ $STATUS != "MOUNTED" ] && [ $STATUS != "OPEN" ] ; then
                        echo "$COUNT : Still not mounted"
                        sleep $INTERVAL
                        COUNT=$(($COUNT+1))
                        continue;
                else
                        echo
                        echo "If there is an error, BCT is enabled but Oracle can't find the file (ORA-27037)"
                        echo "This is normal, I'll procede with the disable to avoid the error at the end of the duplicate."
                        sqlplus -s / as sysdba <<EOF 2>/dev/null
                        whenever sqlerror exit SQL.SQLCODE;
                        set head off feed off
                        select status from v\$block_change_tracking where status='ENABLED';
EOF
                        # if i get an error, BCT is enabled but Oracle can't find the file (ORA-27037)
                        if [ $? -eq 0 ] ; then
                                echo "BCT already disabled"
                        else
                                echo "Got the error. Let's disable the BCT!"
                                disable_trk
                        fi
                        break;
                fi
        else
                echo "$COUNT : Still not mounted"
                sleep $INTERVAL
                COUNT=$(($COUNT+1))
                continue;
        fi
done

Run it  just before the duplicate! e.g.

/u01/app/oracle/local/bin/disable_trk_dup.sh $ORACLE_SID &
rman target=... auxiliary=...

HTH

—

Ludovico