Show DDL for create Oracle DB table

Default long size is only 80. If your DDL is longer you will have to increase the long size to display full DDL. The GET_DDL may not exactly match what was used for creating the table as it will list the default optional settings as well that the actual create table script may have omitted. 

SQL> set long 200000

SQL> select DBMS_METADATA.GET_DDL('TABLE','<your_table_name>') from dual;

Enable/Disable Optional Oracle 11g Options

In Oracle database 11g, after installation, if you ever want to enable/disable the optional features, just shutdown your database and use the chopt utility as described below. Once done, restart the database and you are all set!

$ORACLE_HOME/chopt

Usage:

chopt <enable|disable> <option>

options:
                  dm = Oracle Data Mining RDBMS Files
                  dv = Oracle Database Vault option
                lbac = Oracle Label Security
                olap = Oracle OLAP
        partitioning = Oracle Partitioning
                 rat = Oracle Real Application Testing

e.g. chopt enable rat

Fixing Time Sync problem in Xen DOMU on Oracle VM Server

A 0 in the following suggests syncing time with DOM0:
/proc/sys/xen/independent_wallclock

However, when DOMU is unable to keep time sync with DOM0, the following may be tried:
echo 1 > /proc/sys/xen/independent_wallclock

If you have a ntpd setup elsewhere:
/usr/sbin/ntpdate <ntpd_server>

To update over the network:
rdate -s http://time-a.nist.gov

To manually set the date:
date -s "<date>

Simple Oracle listener.ora

$ORACLE_HOME/network/admin/listener.ora:
listener= (ADDRESS_LIST =
(ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521))
)

SID_LIST_listener = (SID_LIST=
(SID_DESC=(SID_NAME=)(ORACLE_HOME=))
)


--

$ lsnrctl <start|stop|status>

Drop missing data file on ORA-01110

* May not be appropriate in production env *

Sometimes in test env, if a datafile, which is no longer required, is deleted without first dropping the tablespace, then to cleanup:

startup mount;
alter database datafile '' offline drop;
alter database open;
drop tablespace including contents;

Configuring HugePages with Oracle JRockit JVM

Making JRockit JVM use Linux hugepages requires the following 2 configurations:

[1] Mount hugetlbfs
mount -t hugetlbfs nodev /mnt/hugepages
chmod 777 /mnt/hugepages

[2] Use JVM options
-XXaggressive: usually auto enables hugepages, and will use hugepages, if enough available
-Xlargepages: explicitely enables hugepages, and will use if enough hugepages are configured on the system
-Xlargepages:exitOnFailure=true: Will exit if could not use hugepages for any reason

Editing Xen System.img

This post is useful when you want to change system configuration files of a stopped guest VM without botting up the guest first. This method can be used especially when your guest VM crashes or hangs during boot up due to a configuration error.


The following steps have been tested on Xen 4 and Oracle VM 2.2 as well for a Linux guest VM. From DOM0: 


Check FS Type
fdisk -u -l System.img

If FS type is ext3, you can directly mount a partition using lomount, otherwise follow the mounting LV's steps.

Mount Ext3 Partitions

Linux system.img with ext3 partitions can be mounted as:
lomount -diskimage System.img -partition 2 /mnt

Mounting LV's

# Mounting guest's root partition locally
# Find a free loop device
loop_dev=`losetup -f`

# Now bind the image file to that loop device
losetup ${loop_dev} System.img

# Next, scan the loop device for partitions
kpartx -av ${loop_dev}

# If /dev/mapper doesn't list LVs for the partitions from kpartx, find LV:
vgscan
vgchange -ay sysvg

# Mount the desired LVM
mount /dev/mapper/loop0p2 /mnt

LVs UnMounting
# After editing in /mnt, unmount and remove partitions:
umount /mnt

# Disable the LV
vgchange -an /dev/mapper/loop0p2

# Remove the discovered partitions
kpartx -dv ${loop_dev}

# Delete the loop device
losetup -d ${loop_dev}