Query to check blocking sessions in Oracle database

 Query to check blocking sessions in Oracle database from v$lock:

SELECT DECODE(request,0,'Holder: ','Waiter: ') || sid sess,
  id1,
  id2,
  lmode,
  request,
  type
FROM v$lock
WHERE (id1, id2, type) IN
  (SELECT id1, id2, type FROM v$lock WHERE request > 0
  )
ORDER BY id1,
  request;

Useful srvctl commands

Useful srvctl commands for ORACLE RAC MAINTENANCE

srvctl -help or srvctl -v

srvctl commands to startup database:

srvctl start database -d db_name [-o start_options] [-c connect_str|-q]

srvctl start database -d db_name [-o open]

srvctl start database -d db_name -o nomount

srvctl start database -d db_name -o mount

srvctl commands to shutdown database:

srvctl stop database -d db_name [-o stop_options] [-c connect_str|-q]

srvctl stop database -d db_name [-o normal]

srvctl stop database -d db_name -o transactional

srvctl stop database -d db_name -o immediate

srvctl stop database -d db_name -o abort

srvctl config database

srvctl config database -d db_name [-a] [-t]

srvctl start listener -n node_name [-l listener_names]

srvctl stop listener -n node_name [-l listener_names]

srvctl status listener [-n node_name] [-l listener_names] 

srvctl config listener -n node_name

What is Split Brain Syndrome in Oracle RAC?

Split brain syndrome occurs when the Oracle RAC nodes are unable to communicate with each other via private interconnect, but the communication between client and RAC node is maintained. This can cause data Integrity issues  when the same block is read or updated by two nodes and changes done from one node are overwritten by the other node because the block being changed is not locked.

When a node fails, the failed node is prevented from accessing all the shared disk devices and groups. This methodology is called I/O Fencing, Disk Fencing or Failure Fencing.

The node which first detects that one of the node is not accessible will evict that node from the RAC cluster group.This problem is solved by configuring the heartbeat connections through the same communication channels that are used to access the clients.

What is Flashback feature in Oracle Database?

Oracle Flashback Database and restore points are related data protection features that enable you to rewind data back in time to correct any problems caused by logical data corruption or user errors within a designated time window.

Points to Remember

- Flashback Database command can be run either from SQLPLUS or using RMAN Utility.

- FLASHBACK DATABASE command can be used to rewind the database to a target time, SCN or a log sequence number.

- Flashback command works by undoing the changes made to the data files that exist when you run the command.

- Flashback can fix only logical failures, not physical failures.

- If the database control file is restored from backup or re-created, then all existing flashback log information is discarded.

- Avoid using FLASHBACK DATABASE with a target time or SCN that coincides with a NOLOGGING operation, it can cause block corruption.

How to enable Flashback Database feature in Oracle?

 Prerequisites for Flashback Database and Guaranteed Restore Points

Flashback Database

Configure the following database settings before enabling Flashback Database:

-Your database must be running in ARCHIVELOG mode.

-You must have a fast recovery area enabled.

-For Oracle Real Application Clusters (Oracle RAC) databases, the fast recovery area must be in a clustered file system or in ASM.

Guaranteed Restore Points

To use guaranteed restore points,the COMPATIBLE initialization parameter must be set to 10.2.0 or greater.

Steps to enable Flashback Database:

1. Connect to sqlplus as sysdba and set  the desired value for Flashback retention target using below command.

SQL>ALTER SYSTEM SET DB_FLASHBACK_RETENTION_TARGET=4320;

Here, Flashback retention target is set to window of 3 days(4320 Minutes), default value is 1 day (1440 Minutes).

2. Enable the Flashback Database feature for the whole database using the following command:

SQL>ALTER DATABASE FLASHBACK ON;

3.Use the following command to check if Flashback Database is enabled for your target database:

SQL>SELECT FLASHBACK_ON FROM V$DATABASE;

Steps to create Database link from Oracle Database to Microsoft SQLServer Database:

Steps to create Database link from Oracle Database to Microsoft SQLServer Database:

Pre-requisites

1. Check Network communication is Opened from Oracle Database Server to MSSQL Database Server using telnet
2. Download the Oracle Gateway Server Software same as your Oracle Database version.

Installation of Oracle Gateway Software
=========

Hope you have downloaded the Dg4msql software for sql server 

1> Create a directory as gateway under $ORACLE_BASE directory. 

2) Invoke the GUI , Select Oracle Gateway for MYSQL and enter the sql server details at the time of installation 

3) Before completing the installation, OUI invokes the NETCA and create a new listener for gateway with new port (ex:1526) 

Note; In case if you have defined any bash profile for TNS_ADMIN, then please comment it 

4. Follow the below note for pre-req for gateway listener 

How to Configure DG4MSQL (Oracle Database Gateway for MS SQL Server) 64bit Unix OS (Linux, Solaris, AIX,HP-UX) post install ( Doc ID 562509.1 ) 

edit your gateway listener as recommended in the above note. 

5. create a tnsentry in $ORACLE_HOME/network/admin 

6. export TNS_ADMIN=$gateway home/network/admin 

lsnrctl stop <gateway listener> 

lsnrctl start <gateway listener> 

tnsping <gateway alias> 

conn / as sysdba 

create public database link <test> connect to "<sql server user>" identified by "<password>" using '<tnsnames.ora>' 

select * from dual@test; 

Script to check free space and used space in Oracle Database tablespaces

select a.tablespace_name,
       a.bytes_alloc/(1024*1024) "TOTAL ALLOC (MB)",
 a.physical_bytes/(1024*1024) "TOTAL PHYS ALLOC (MB)",
       nvl(b.tot_used,0)/(1024*1024) "USED (MB)",
       (nvl(b.tot_used,0)/a.bytes_alloc)*100 "% USED"
from ( select tablespace_name,
       sum(bytes) physical_bytes,
sum(decode(autoextensible,'NO',bytes,'YES',maxbytes)) bytes_alloc
       from dba_data_files
       group by tablespace_name ) a,
     ( select tablespace_name, sum(bytes) tot_used
       from dba_segments
group by tablespace_name ) b
where a.tablespace_name = b.tablespace_name (+)
--and   (nvl(b.tot_used,0)/a.bytes_alloc)*100 > 10
and   a.tablespace_name not in (select distinct tablespace_name from dba_temp_files)
and   a.tablespace_name not like 'UNDO%'
order by 1
 --order by 5
/ 

RMAN-03009: failure of allocate command on ORA_AUX_SBT_TAPE_1 channel

This is an error during Database Clone using RMAN. I was trying to restore database using RMAN Backup 

RMAN-00571: ===========================================================

RMAN-00569: ===============
ERROR MESSAGE STACK FOLLOWS ===============

RMAN-00571: ===========================================================

RMAN-03002: failure of Duplicate Db command
RMAN-05501: aborting duplication of target database

RMAN-03009: failure of allocate command on ORA_AUX_SBT_TAPE_1 channel 
ORA-19554: error allocating device, device type: SBT_TAPE, device name:

ORA-27211: Failed to load Media Management Library

Additional information: 

Cause: Backup Configuration was modified.

Solution:
Use the below command to Resolve the error and continue with Database Restore

rman auxiliary / 
run
{
allocate auxiliary channel c1 type disk;
allocate auxiliary channel c2 type disk;
duplicate database to 'DEV' backup location '/Daily_Backup/Backup_16042018';
}
exit;
EOF

How to add space in ACFS filesystem?

The below post explains the step-by-step process to add storage to a mountpoint in ACFS filesystem

1.Before extending the mountpoint storage we need to add an LVM of required Storage Capacity on the server.

For checking the LUN's available on the server, click here

For now, assume the LUN added is /dev/sdf1

2. As root User, check the available disks by running the below command

$ /usr/sbin/oracleasm listdisks
DATA01
OCR_VOTE01
OCR_VOTE02
OCR_VOTE03

3. Create a new disk using the below command

/usr/sbin/oracleasm createdisk DATA02 /dev/sdf1 

Where DATA02 is the name of new disk added
/dev/sdf1 is the LUN added for storage extension.

4. Verify the disk is added by running the below command.

 $/etc/init.d/oracleasm  listdisks
DATA01
DATA02
OCR_VOTE01
OCR_VOTE02
OCR_VOTE03

5. Navigate to the other cluster nodes and run the scandisks command to reflect the newly added disk on all the nodes of cluster.

$/etc/init.d/oracleasm  scandisks
Scanning the system for Oracle ASMLib disks:               [  OK  ]

 $/etc/init.d/oracleasm  listdisks
DATA01
DATA02
OCR_VOTE01
OCR_VOTE02
OCR_VOTE03

6. Now login to the database server as GRID user (Where ASM instance is running) to add space to ACFS.

Set the environment as required


export ORACLE_HOME=/u01/app/12.1.0/grid
export PATH=$PATH:$ORACLE_HOME/bin
export ORACLE_SID=+ASM1

$sqlplus / as sysasm

SQL> alter diskgroup DATA add disk '/dev/oracleasm/disks/DATA02';

Diskgroup altered.


7. Increase the space on filesystem

As root user,

$acfsutil size +1G /oradata
acfsutil size: new file system size: 591833071616 (564416MB)

How to Enable Database Vault in Oracle database Version 11gR1?

Steps to enable Database Vault in Oracle Database 11gR1:

1. In the command prompt, use DVCA utility to enable Oracle Database Vault.

e.g.

dvca -action enable 
  -oh /u01/app/oracle/product/11.1.0/db_1
  -service conn_alias 
  -instance orcl 
  -dbname orcl 
  -owner_account lbrown_dvowner 
  -logfile dvcalog.txt 

Enter SYS password: sys_password
Enter owner password: owner_password

Parameter Description:
======================

-service is the name of the database specifier. The specifier can be a connect descriptor or net service name. 

-instance is the name of the database instance.

-dbname is the database name.

-sys_passwd is the SYS password. If you use a cleartext password on the command line, you must include the nodecrypt option. If you omit the password, DVCA prompts you for it. Preferably, omit the password and then enter it interactively when prompted.

-owner_account is the Oracle Database Vault Owner account name.

-owner_passwd is the Oracle Database Vault Owner account password. If you use a cleartext password on the command line, you must include the nodecrypt option. If you omit the password, DVCA prompts you for it. Preferably, omit the password and then enter it interactively when prompted.

-logfile is an optional flag to specify a log file name and location. You can enter an absolute path, or enter a path that is relative to the location of the $ORACLE_HOME/bin directory.

-silent is the option to run in command line mode. This option is required if you are not running DVCA in an xterm window.

-nodecrypt is the option to read plaintext passwords.

-lockout is the flag to use to disable SYSDBA operating system authentication.

2. Stop the database, Database Control console process, and listener.

Enable the Oracle Database Vault option as follows:
 The make command enables both Oracle Database Vault (dv_on) and Oracle Label Security (lbac_on).
 You must enable Oracle Label Security before you can use Database Vault.

cd $ORACLE_HOME/rdbms/lib
make -f ins_rdbms.mk dv_on lbac_on

cd $ORACLE_HOME/bin
relink all

3.Restart the database, Database Control console process, and listener.

4. Verify Oracle Database Vault and Oracle Label Security are enabled.

SELECT * FROM V$OPTION WHERE PARAMETER = 'Oracle Label Security';

SELECT * FROM V$OPTION WHERE PARAMETER = 'Oracle Database Vault';

How to create a Database link in GL to transfer FSG reports?

Some times, to migrate FSG reports from one environment to the other, its easy to create a dblink between the source and target environemnts and transfer the reports.

STep-by-Step Process to create database link using General Ledger Responbility.

1. Ensure that network connectivity is open between the Source and Target environments.

2. Login to database node of source instance and copy the contents of tnsnames.ora


Extract from tnsnames.ora

TEST1=
        (DESCRIPTION=
                (ADDRESS=(PROTOCOL=tcp)(HOST=localhost.domain.com)(PORT=1524))
            (CONNECT_DATA=
                (SID=TEST1)
            )
        )

4. Add the above tns entry in the tnsnames.ora file on the application server node of Target instance (Where db link need to be created)


5. Format the tns entry into a single line as below


(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=localhost.domain.com)(PORT=1524))(CONNECT_DATA=(SID=TEST1)))


6. Navigate to General Ledger Superuser Reponsibility.

Click on SEtup->>System--> Database links

A form will popup --> Click on "New Database Link"

Input the below values

Database Name: TEST1
Description :Database link for FSG reports
Connect String:
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=localhost.domain.com)(PORT=1524))(CONNECT_DATA=(SID=TEST1)))
DOMAIN Name: DOMAIN.COM
Apps Username: APPS
APPS Password: <Password>

7. Verify that db link is created

select * from dba_db_links;

How to create directories in Oracle Database?

Database Directories are required to read/write to a filesystem location from plsql code.

Below is the syntax to create database directory

SQL> create directory PLSQL_DIR AS '/oratmp/code';

Directory created.

Grant Read/write privileges to Required Schema (e.g . APPS)

SQL> GRANT READ,WRITE ON DIRECTORY PLSQL_DIR TO APPS;

Grant succeeded.

How to use coe_xfr_sql_profile.sql to Improve performance of a sql query?

Oracle SQL Performance tuning is one of the frequently reported issues in a Oracle Database administrator's daily job.
Very often we notice that sql queries or concurrent Programs which were running within few minutes earlier are now taking hours to be completed.
Underlying reason is due to the plan_hash_value used by the query has been changed.
coe_xfr_sql_profile.sql is the script developed by Oracle Support which helps us to identify the plan_hash_value which will resolve the performance issue.

Steps to use the script coe_xfr_sql_profile.sql

1. Download the script to a temporary directory on the database server.
Script is also available in Oracle Metalink.

2. Before Running the coe_xfr_sql_profile.sql, we need to know the sql_id of the sql query which is taking longer time to complete than usual.

To find the sql_id use below query

2.1 If you know the database SID of the long running query.
select inst_id,sid,serial#,status,last_Call_et,sql_id from gv$session where sid= '&sessionid';

2.2 If you know the query test, Use gv$sql and gv$sqlarea views to get the sql_id.

3. Login to sqlplus as sysdba and run coe_xfr_sql_profile.sql at the SQL prompt.

$ sqlplus “/as sysdba”
SQL> @coe_xfr_sql_profile.sql
Parameter 1:
SQL_ID (required)

Enter value for 1: 0a3f7vuks8d7y   (--this is the sql_id of long running sql)
PLAN_HASH_VALUE AVG_ET_SECS
————— ———–
1484137450 15.6
3622468234 4560.76

[Output shows the list of available plan hash values, which can be forced on to the sql query. We need to select the plan_hash_value with low ETA to resolve the performance issue]

Parameter 2:
PLAN_HASH_VALUE (required)

Enter value for 2: 1484137450 


++Based on the inputs provided, it generates a sql script with naming convention coe_xfr_sql_profile_0a3f7vuks8d7y_1484137450.sql as output

coe_xfr_sql_profile_<sql_id>_<plan_hash_value>.sql

4. Run the script as sysdba

SQL>coe_xfr_sql_profile_0a3f7vuks8d7y_1484137450.sql 

5. Verify that Performance issue is resolved by Re-running the sql.

How to check if Oracle Database Vault is enabled?

Below sql query can help us to identify if Oracle Database Vault is enabled or Disabled

SQL> SELECT * FROM V$OPTION WHERE PARAMETER = 'Oracle Database Vault';

PARAMETER                                          VALUE        CON_ID
-------------------------------------------------- -------- ----------
Oracle Database Vault                              FALSE             0


Database Vault is Disabled.

How to Resolve ACFS-03008 : The volume expansion limit has been reached?

Issue: ACFS Filesystem resize operation fails with "ACFS-03008: The volume could not be resized.  The volume expansion limit has been reached."

$acfsutil size +1G /oradata
acfsutil size: ACFS-03008: The volume could not be resized.  The volume expansion limit has been reached.
acfsutil size: ACFS-03216: The ADVM compatibility attribute for the diskgroup was below the required version (11.2.0.4.0) for unlimited volume expansions.

Analysis:

Compatible attribute for advm and rdbms is below the required version.

 SQL>  select group_number, name, value from v$asm_attribute where name like 'compatible%' ;

GROUP_NUMBER
------------
NAME
--------------------------------------------------------------------------------
VALUE
--------------------------------------------------------------------------------
           1
compatible.asm
12.1.0.0.0

           1
compatible.rdbms
11.2.0.0.0

           1
compatible.advm
11.2.0.0.0

           2
compatible.asm

12.1.0.0.0

           2
compatible.rdbms
10.1.0.0.0




Solution:

SQL> ALTER DISKGROUP DATA SET ATTRIBUTE 'compatible.advm'='11.2.0.4.0' ;

Diskgroup altered.

SQL>  ALTER DISKGROUP DATA SET ATTRIBUTE 'compatible.rdbms'='11.2.0.4.0' ;

Diskgroup altered.

Now verify the issue is resolved.
$ acfsutil size +10G /oradata
acfsutil size: new file system size: 603644231680 (575680MB)

ACFS-03171: Insufficient contiguous free ASM Diskgroup space

Issue:  

ACFS file resize operation operation fails with ACFS-03171: Insufficient contiguous free ASM Diskgroup space


[root@erptestdb01 ~]# cd /sbin
[root@erptestdb01 sbin]# acfsutil size +100M /oradata
acfsutil size: ACFS-03171: Insufficient contiguous free ASM Diskgroup space.  Check the ASM alert log.

Solution:

Increase size in smaller chunks until the required size is reached
[root@erptestdb01 bin]# acfsutil size +10M /oradata
acfsutil size: new file system size: 590625112064 (563264MB)

What are the features of BIGFILE Tablespace in Oracle Database?

Bigfile Tablespace is introduced from Oracle 10g.A bigfile tablespace is a tablespace with a single, but very large (up to 4G blocks) datafile.

The benefits of bigfile tablespaces are the following:

A bigfile tablespace with 8K blocks can contain a 32 terabyte datafile. A bigfile tablespace with 32K blocks can contain a 128 terabyte datafile. The maximum number of datafiles in an Oracle Database is limited (usually to 64K files). Therefore, bigfile tablespaces can significantly enhance the storage capacity of an Oracle Database.

Bigfile tablespaces can reduce the number of datafiles needed for a database. 
An additional benefit is that the DB_FILES initialization parameter and MAXDATAFILES parameter of the CREATE DATABASE and CREATE CONTROLFILE statements can be adjusted to reduce the amount of SGA space required for datafile information and the size of the control file.

Bigfile tablespaces simplify database management by providing datafile transparency. 
SQL syntax for the ALTER TABLESPACE statement lets you perform operations on tablespaces, 
rather than the underlying individual datafiles.

Bigfile tablespaces are intended to be used with Automatic Storage Management (ASM) or other logical volume managers that supports striping or RAID, and dynamically extensible logical volumes.

Avoid creating bigfile tablespaces on a system that does not support striping because of negative implications for parallel query execution and RMAN backup parallelization.


Creating a Bigfile Tablespace


To create a bigfile tablespace, specify the BIGFILE keyword of the CREATE TABLESPACE statement (CREATE BIGFILE TABLESPACE ...)

CREATE BIGFILE TABLESPACE bigtbs 
    DATAFILE '/u02/oracle/data/bigtbs01.dbf' SIZE 50G
...


Identifying a Bigfile Tablespace

The following views contain a BIGFILE column that identifies a tablespace as a bigfile tablespace:

DBA_TABLESPACES

USER_TABLESPACES

V$TABLESPACE

ORA-32771: Cannot Add File To Bigfile Tablespace

When trying to add a datafile to a tablespace , got the error – ORA-32771: cannot add file to bigfile tablespace.

SQL> ALTER TABLESPACE BIG_TBSP1 add datafile ‘+DATA/df01.dbf’ size 130G;
ALTER TABLESPACE BIG_TBSP1 add datafile ‘+DATA/df01.dbf’ size 130G;
*
ERROR at line 1:
ORA-32771: cannot add file to bigfile tablespace

SOLUTION:

A bigfile tablespace can contain only one datafile and no other datafile can be added to that.

SQL> select BIGFILE from dba_tablespaces where tablespace_name=’BIG_TBSP1’;

BIGFILE
———————– —
YES

How to increase space in Bigfile Tablespace?


BIGFILE tablespace stores its data in a single datafile with a much larger capacity.

We can resize the size of the datafile in BIGFILE tablespace using ALTER DATABASE Command


ALTER DATABASE DATAFILE '/+DATA/df0101.dbf' RESIZE 180G;

Since BIGFILE Tablespace has only one datafile, there is no need to identify the datafile and increase its size.
We can use ALTER TABLESPACE command to resize at the tablespace level.

ALTER TABLESPACE BIG_TBSP1 RESIZE 180G;

How to Use Logon Trigger to trace sessions connected to Oracle database?

To start tracing:

create or replace trigger user_logon_trg
after logon on database
begin
if USER = 'xxxx' then
execute immediate
'Alter session set events ''10046 trace name context forever, level 8''';
end if;
end;
/

/* Login a new session as User 'xxxx' and execute your selects to be traced */


NOTE: The following syntax can also be used within the if logic to also get the user name or to add more granularity by specifying a host name where the connection originated.

IF SYS_CONTEXT('USERENV','SESSION_USER') = '<USER_NM>' AND SYS_CONTEXT('USERENV','HOST') = '<HOST_NM>' THEN

To stop tracing: via LogOff Trigger (needs to be created before logging off)

create or replace trigger user_logoff_trg
before logoff on database
begin
if USER = 'xxxx' then
execute immediate
'Alter session set events ''10046 trace name context off''';
end if;
end;
/

What is the difference between Switchover and Failover in Oracle Dataguard?

A switchover means just switching roles between the primary database and standby db.
nswitchover, the primary database chnaged to a standby role, and the standby database changed to the primary role.
This is typically done for planned maintenance of the primary db server.

A failover is when the primary database fails and one of the standby databases is 
transitioned to take over the primary role. Failover is performed only in the event 
of a catastrophic failure of the primary database, and there is no possibility of 
recovering the primary database in a timely manner. Failover may or may not result 
in data loss depending on the protection mode in effect at the time of the failover.