Oracle DBA Quick Notes: Interview Questions & Answers

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Friday, September 4, 2020

Configure Quorum Disk in Exadata

In last article[click here] - we learnt how to remove quorum disk from the Exadata system, now here we would see it we add and configure that.

Before we are adding quorum disk configuration in the system, you need to have IB switches interface names, ASM binary owner and group handy as that is required to create the config.

[root@exa01dbadm01 oracle.SupportTools]# /opt/oracle.SupportTools/quorumdiskmgr --create --config --owner=oragrid --group=asmadmin --network-iface-list="ib0, ib1"
[Info] Successfully created iface exadata_ib0 with iface.net_ifacename ib0
[Info] Successfully created iface exadata_ib1 with iface.net_ifacename ib1
[Success] Successfully created quorum disk configurations

[root@exa01dbadm01 oracle.SupportTools]#

Do the same as above on node2 as well.

[root@exa01dbadm02 oracle.SupportTools]# /opt/oracle.SupportTools/quorumdiskmgr --create --config --owner=oragrid --group=asmadmin --network-iface-list="ib0, ib1"
[Info] Successfully created iface exadata_ib0 with iface.net_ifacename ib0
[Info] Successfully created iface exadata_ib1 with iface.net_ifacename ib1
[Success] Successfully created quorum disk configurations

[root@exa01dbadm02 oracle.SupportTools]#

Check if the quoum disk configuration is created as below from node1 and node2.

[root@exa01dbadm01 oracle.SupportTools]# /opt/oracle.SupportTools/quorumdiskmgr --list --config
Owner: oragrid
Group: asmadmin
ifaces: exadata_ib1 exadata_ib0
Initiatior name: iqn.1988-12.com.oracle:192.168.10.1

[root@exa01dbadm01 oracle.SupportTools]#

[root@exa01dbadm02 oracle.SupportTools]# /opt/oracle.SupportTools/quorumdiskmgr --list --config
Owner: oragrid
Group: asmadmin
ifaces: exadata_ib1 exadata_ib0
Initiatior name: iqn.1988-12.com.oracle:192.168.10.3

[root@exa01dbadm02 oracle.SupportTools]#

Now, create quorum disk target for DATAC1 diskgroup which is visible to both compute nodes, before it you need to identify IB interface IPs of both nodes as that is required here.

Run the command on node1 and node2.

[root@exa01dbadm01 oracle.SupportTools]# /opt/oracle.SupportTools/quorumdiskmgr --create --target --asm-disk-group=datac1 --visible-to="192.168.10.1, 192.168.10.2, 192.168.10.3, 192.168.10.4"
[Success] Created logical volume /dev/VGExaDb/LVDbVdexa01dbadm01DATAC1.
[Success] Created backstore QD_DATAC1_exa01dbadm01.
[Success] Created target iqn.2015-05.com.oracle:qd--datac1--exa01dbadm01.

[root@exa01dbadm01 oracle.SupportTools]#

[root@exa01dbadm02 oracle.SupportTools]# /opt/oracle.SupportTools/quorumdiskmgr --create --target --asm-disk-group=datac1 --visible-to="192.168.10.1, 192.168.10.2, 192.168.10.3, 192.168.10.4"
[Success] Created logical volume /dev/VGExaDb/LVDbVdexa01dbadm02DATAC1.
[Success] Created backstore QD_DATAC1_exa01dbadm02.
[Success] Created target iqn.2015-05.com.oracle:qd--datac1--exa01dbadm02.

[root@exa01dbadm02 oracle.SupportTools]#

Now you can list the quorum disk targets on node1 and node2 as below to validate.

[root@exa01dbadm01 oracle.SupportTools]# /opt/oracle.SupportTools/quorumdiskmgr --list --target
Name: iqn.2015-05.com.oracle:qd--datac1--exa01dbadm01
Host name: exa01dbadm01
ASM disk group name: DATAC1
Visible to: iqn.1988-12.com.oracle:192.168.10.1, iqn.1988-12.com.oracle:192.168.10.2, iqn.1988-12.com.oracle:192.168.10.3, iqn.1988-12.com.oracle:192.168.10.4
Discovered by:


[root@exa01dbadm01 oracle.SupportTools]#

[root@exa01dbadm02 oracle.SupportTools]# /opt/oracle.SupportTools/quorumdiskmgr --list --target
Name: iqn.2015-05.com.oracle:qd--datac1--exa01dbadm02
Host name: exa01dbadm02
ASM disk group name: DATAC1
Visible to: iqn.1988-12.com.oracle:192.168.10.1, iqn.1988-12.com.oracle:192.168.10.2, iqn.1988-12.com.oracle:192.168.10.3, iqn.1988-12.com.oracle:192.168.10.4
Discovered by:


[root@exa01dbadm02 oracle.SupportTools]#

Create quorum disk device as below on node1 and node2.

[root@exa01dbadm01 oracle.SupportTools]# /opt/oracle.SupportTools/quorumdiskmgr --create --device --target-ip-list="192.168.10.1, 192.168.10.2, 192.168.10.3, 192.168.10.4"
[Success] Successfully created all device(s) from target(s) on machine with IP address 192.168.10.1

[Success] Successfully created all device(s) from target(s) on machine with IP address 192.168.10.2

[Success] Successfully created all device(s) from target(s) on machine with IP address 192.168.10.3

[Success] Successfully created all device(s) from target(s) on machine with IP address 192.168.10.4

[root@exa01dbadm01 oracle.SupportTools]#

[root@exa01dbadm02 oracle.SupportTools]# /opt/oracle.SupportTools/quorumdiskmgr --create --device --target-ip-list="192.168.10.1, 192.168.10.2, 192.168.10.3, 192.168.10.4"
[Success] Successfully created all device(s) from target(s) on machine with IP address 192.168.10.1

[Success] Successfully created all device(s) from target(s) on machine with IP address 192.168.10.2

[Success] Successfully created all device(s) from target(s) on machine with IP address 192.168.10.3

[Success] Successfully created all device(s) from target(s) on machine with IP address 192.168.10.4

[root@exa01dbadm02 oracle.SupportTools]#

Now you can list the quorum disk device on node1 and node2 to validate.

[root@exa01dbadm01 oracle.SupportTools]# /opt/oracle.SupportTools/quorumdiskmgr --list --device
Device path: /dev/exadata_quorum/QD_DATAC1_exa01dbadm01
Host name: exa01dbadm01
ASM disk group name: DATAC1
Size: 128 MB

Device path: /dev/exadata_quorum/QD_DATAC1_exa01dbadm02
Host name: exa01dbadm02
ASM disk group name: DATAC1
Size: 128 MB


[root@exa01dbadm01 oracle.SupportTools]#

[root@exa01dbadm02 oracle.SupportTools]# /opt/oracle.SupportTools/quorumdiskmgr --list --device
Device path: /dev/exadata_quorum/QD_DATAC1_exa01dbadm02
Host name: exa01dbadm02
ASM disk group name: DATAC1
Size: 128 MB

Device path: /dev/exadata_quorum/QD_DATAC1_exa01dbadm01
Host name: exa01dbadm01
ASM disk group name: DATAC1
Size: 128 MB


[root@exa01dbadm02 oracle.SupportTools]#

Now, check in the ASM instance if quorum disk devices are visible to ASM to be used for the DATAC1 diskgroup as below, we can see that quorum disk devices are available as CANDIDATE disks that we can add in to the diskgroup.

SQL> l
  1* SELECT inst_id, label, path, mode_status, header_status FROM gv$asm_disk WHERE path LIKE '/dev/exadata_quorum/%'
SQL> /

   INST_ID LABEL                           PATH                                                                   MODE_ST HEADER_STATU
---------- ------------------------------- ---------------------------------------------------------------------- ------- ------------
         1 QD_DATAC1_exa01dbadm02      /dev/exadata_quorum/QD_DATAC1_exa01dbadm02                         ONLINE  CANDIDATE
         1 QD_DATAC1_exa01dbadm01      /dev/exadata_quorum/QD_DATAC1_exa01dbadm01                         ONLINE  CANDIDATE
         2 QD_DATAC1_exa01dbadm02      /dev/exadata_quorum/QD_DATAC1_exa01dbadm02                         ONLINE  CANDIDATE
         2 QD_DATAC1_exa01dbadm01      /dev/exadata_quorum/QD_DATAC1_exa01dbadm01                         ONLINE  CANDIDATE

SQL>

Add the quorum devices in to the diskgroup as below.

SQL> ALTER DISKGROUP datac1 ADD QUORUM FAILGROUP exa01dbadm01 DISK '/dev/exadata_quorum/QD_DATAC1_exa01dbadm01'
QUORUM FAILGROUP exa01dbadm02 DISK '/dev/exadata_quorum/QD_DATAC1_exa01dbadm02';  2

Diskgroup altered.

SQL>

After disk addition, we can see that now these are parts of diskgroup and status is MEMBER.

SQL> SELECT inst_id, label, path, mode_status, header_status
FROM gv$asm_disk WHERE path LIKE '/dev/exadata_quorum/%';  2

   INST_ID LABEL                           PATH                                                                   MODE_ST HEADER_STATU
---------- ------------------------------- ---------------------------------------------------------------------- ------- ------------
         1 QD_DATAC1_exa01dbadm02      /dev/exadata_quorum/QD_DATAC1_exa01dbadm02                         ONLINE  MEMBER
         1 QD_DATAC1_exa01dbadm01      /dev/exadata_quorum/QD_DATAC1_exa01dbadm01                         ONLINE  MEMBER
         2 QD_DATAC1_exa01dbadm02      /dev/exadata_quorum/QD_DATAC1_exa01dbadm02                         ONLINE  MEMBER
         2 QD_DATAC1_exa01dbadm01      /dev/exadata_quorum/QD_DATAC1_exa01dbadm01                         ONLINE  MEMBER

SQL>

Finally, replaced/moved the voting disks back to DATAC1 diskgroup and five copies of files are now available.

[root@exa01dbadm02 oracle.SupportTools]# crsctl query css votedisk
##  STATE    File Universal Id                File Name Disk group
--  -----    -----------------                --------- ---------
 1. ONLINE   cf9c32d1c0c34fafbf47caa1b77821b0 (o/10.0.0.5;10.0.0.6/DATAC1_CD_02_exad02cel01) [DATAC1]
 2. ONLINE   e2e61cd646224f08bf2c4c47e719e8fd (o/10.0.0.3;10.0.0.4/DATAC1_CD_05_exad02cel02) [DATAC1]
 3. ONLINE   7691da5101a34f95bfc56c3bec4e681b (o/10.0.0.1;10.0.0.2/DATAC1_CD_03_exad02cel03) [DATAC1]
 4. ONLINE   3dea97bdc5aa4f61bf0355abe31c1361 (/dev/exadata_quorum/QD_DATAC1_exa01dbadm02) [DATAC1]
 5. ONLINE   cc5671a086eb4f38bf5c690666099d66 (/dev/exadata_quorum/QD_DATAC1_exa01dbadm01) [DATAC1]
Located 5 voting disk(s).
[root@exa01dbadm02 oracle.SupportTools]#

After CRS restart : I bounced the CRS on both nodes to check if things are coming up normally.

[root@exa01dbadm02 oracle.SupportTools]# crsctl query css votedisk
##  STATE    File Universal Id                File Name Disk group
--  -----    -----------------                --------- ---------
 1. ONLINE   cf9c32d1c0c34fafbf47caa1b77821b0 (o/10.0.0.5;10.0.0.6/DATAC1_CD_02_exad02cel01) [DATAC1]
 2. ONLINE   e2e61cd646224f08bf2c4c47e719e8fd (o/10.0.0.3;10.0.0.4/DATAC1_CD_05_exad02cel02) [DATAC1]
 3. ONLINE   7691da5101a34f95bfc56c3bec4e681b (o/10.0.0.1;10.0.0.2/DATAC1_CD_03_exad02cel03) [DATAC1]
 4. ONLINE   3dea97bdc5aa4f61bf0355abe31c1361 (/dev/exadata_quorum/QD_DATAC1_exa01dbadm02) [DATAC1]
 5. ONLINE   cc5671a086eb4f38bf5c690666099d66 (/dev/exadata_quorum/QD_DATAC1_exa01dbadm01) [DATAC1]
Located 5 voting disk(s).
[root@exa01dbadm02 oracle.SupportTools]#

Our missing quorum disk issue stands fixed here......!!

Hope it helps, thanks for reading, please subscribe to this blog to stay updated with latest news on Oracle Cloud Infrastructure and Oracle Autonomous Database Cloud Services and new articles.

Twitter : https://twitter.com/rajsoft8899

Linkedin : https://www.linkedin.com/in/raj-kumar-kushwaha-5a289219/

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Monday, August 31, 2020

Removing the Quorum Disk Configuration in Exadata

In this blog post, we would see how to remove quorum disks in Exadata machine. We have one 1/8th Rack Exadata machine for Lab activity where ran into missing quorum disks for Voting Disk and I had to fix that in order to get the system patched in Rolling fashion to maintain high availability.

To patch the Exadata system in rolling fashion, it requires voting disks to reside on HIGH redundancy diskgroup which is not possible in 1/8th Rack Exadata system since there is only 3 cell nodes in there, and for High redundancy it requires five copies of voting disk.

So, in this scenario - we add a separate HDD drive on both compute nodes and share that between the nodes to be used for High redundancy diskgroup creation - there it comes the term "Quorum Disk"

We have +DATAC1 diskgroup configured with HIGH redundancy where our voting disk resides but two of the quorum disks being used in there went missing so our voting disks had only three copies available and CRS was not coming up.

I had to remove the quorum disks from both compute nodes and then configure it back to fix the issue.

SQL> l 
  1* select disk_number, GROUP_NUMBER, MOUNT_STATUS, HEADER_STATUS, MODE_STATUS, STATE, path from v$asm_disk where GROUP_NUMBER=1
SQL> / 

DISK_NUMBER GROUP_NUMBER MOUNT_S HEADER_STATU MODE_ST STATE    PATH 
----------- ------------ ------- ------------ ------- -------- ---------------------------------------------------------------------- 
          2            1 MISSING UNKNOWN      OFFLINE NORMAL 
          3            1 MISSING UNKNOWN      OFFLINE NORMAL 
         14            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.1;10.0.0.2/DATAC1_CD_05_exad02cel03
         13            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.1;10.0.0.2/DATAC1_CD_00_exad02cel03
         15            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.1;10.0.0.2/DATAC1_CD_02_exad02cel03
          7            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.1;10.0.0.2/DATAC1_CD_03_exad02cel03
          8            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.1;10.0.0.2/DATAC1_CD_04_exad02cel03
          0            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.1;10.0.0.2/DATAC1_CD_01_exad02cel03
          4            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.3;10.0.0.4/DATAC1_CD_05_exad02cel02
         16            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.3;10.0.0.4/DATAC1_CD_02_exad02cel02
         17            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.3;10.0.0.4/DATAC1_CD_01_exad02cel02
          5            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.3;10.0.0.4/DATAC1_CD_00_exad02cel02
          6            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.3;10.0.0.4/DATAC1_CD_03_exad02cel02
         11            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.3;10.0.0.4/DATAC1_CD_04_exad02cel02
         19            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.5;10.0.0.6/DATAC1_CD_04_exad02cel01
          1            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.5;10.0.0.6/DATAC1_CD_02_exad02cel01
         18            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.5;10.0.0.6/DATAC1_CD_00_exad02cel01
          9            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.5;10.0.0.6/DATAC1_CD_03_exad02cel01
         12            1 CACHED  MEMBER       ONLINE  NORMAL   o/10.0.0.5;10.0.0.6/DATAC1_CD_01_exad02cel01

Due to missing quorum disk in the DATAC1 diskgroup, we have only three copies of voting disks available as of now.

[root@exa01dbadm02 ~]# crsctl query css votedisk
##  STATE    File Universal Id                File Name Disk group
--  -----    -----------------                --------- ---------
 1. ONLINE   94acaa401bd34fe0bf261af4437fc75e (o/10.0.0.5;10.0.0.6/DATAC1_CD_02_exad02cel01) [DATAC1]
 2. ONLINE   7680d9f206544ff1bf27661bf8cc3250 (o/10.0.0.3;10.0.0.4/DATAC1_CD_05_exad02cel02) [DATAC1]
 3. ONLINE   b632f75fe4884f5cbf3627faa6bbbe07 (o/10.0.0.1;10.0.0.2/DATAC1_CD_03_exad02cel03) [DATAC1]
Located 3 voting disk(s).
[root@exa01dbadm02 ~]#

I moved the voting disks to +RECOC1 diskgroup which was configured with NORMAL REDUNDANCY.

[oragrid@exa01dbadm01 ~]$ crsctl replace votedisk +RECOC1
Successful addition of voting disk 783e7633ea934fd0bff78c8b8dbe5a66.
Successful addition of voting disk a5cf9e2d99134f69bf6bb15c98044623.
Successful addition of voting disk d5d20cd6ff3e4fcdbf68df28cb18d030.
Successful deletion of voting disk 94acaa401bd34fe0bf261af4437fc75e.
Successful deletion of voting disk 7680d9f206544ff1bf27661bf8cc3250.
Successful deletion of voting disk b632f75fe4884f5cbf3627faa6bbbe07.
Successful deletion of voting disk e47d60407b054f3bbf5dc07df8080ee6.
Successfully replaced voting disk group with +RECOC1.
CRS-4266: Voting file(s) successfully replaced


[oragrid@exa01dbadm01 ~]$ crsctl query css votedisk
##  STATE    File Universal Id                File Name Disk group
--  -----    -----------------                --------- ---------
 1. ONLINE   783e7633ea934fd0bff78c8b8dbe5a66 (o/10.0.0.5;10.0.0.6/RECOC1_CD_02_exad02cel01) [RECOC1]
 2. ONLINE   a5cf9e2d99134f69bf6bb15c98044623 (o/10.0.0.3;10.0.0.4/RECOC1_CD_02_exad02cel02) [RECOC1]
 3. ONLINE   d5d20cd6ff3e4fcdbf68df28cb18d030 (o/10.0.0.1;10.0.0.2/RECOC1_CD_02_exad02cel03) [RECOC1]
Located 3 voting disk(s).
[oragrid@exa01dbadm01 ~]$

Now we can go ahead and drop the missing quorum disks from the DATAC1 diskgroup forcefully.

[oragrid@exa01dbadm01 ~]$ sqlplus "/as sysasm"

SQL*Plus: Release 12.2.0.1.0 Production on Thu Jul 30 12:06:27 2020

Copyright (c) 1982, 2016, Oracle.  All rights reserved.


Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL>
SQL> set lines 300
SQL> ALTER DISKGROUP DATAC1 DROP QUORUM DISK QD_DATAC1_exa01dbadm01 FORCE;

Diskgroup altered.

SQL> ALTER DISKGROUP DATAC1 DROP QUORUM DISK QD_DATAC1_exa01dbadm02 FORCE;

Diskgroup altered.

SQL>

Delete the quorum disk device from the node1 using quorumdiskmgr utility.

[root@exa01dbadm01 ~]# cd /opt/oracle.SupportTools/
[root@exa01dbadm01 oracle.SupportTools]# ./quorumdiskmgr --delete --device
[Success] Successfully deleted device /dev/exadata_quorum/QD_DATAC1_exa01dbadm01.
[Success] Successfully deleted device /dev/exadata_quorum/QD_DATAC1_exa01dbadm02.

Delete the quorum disk target from the node1 using quorumdiskmgr utility.

[root@exa01dbadm01 oracle.SupportTools]# ./quorumdiskmgr --delete --target
[Success] Successfully removed target iqn.2015-05.com.oracle:qd--datac1--exa01dbadm01
[Success] Successfully removed backstore QD_DATAC1_exa01dbadm01
[Success] Successfully removed logical volume /dev/VGExaDb/LVDbVdexa01dbadm01DATAC1

Now delete quorum disk configuration from the node1.

[root@exa01dbadm01 oracle.SupportTools]# ./quorumdiskmgr --delete --config

[Success] Successfully deleted quorum disk configurations

[root@exa01dbadm01 oracle.SupportTools]#

Now, delete the quorum disk device from node2.

[root@exa01dbadm02 ~]# cd /opt/oracle.SupportTools/
[root@exa01dbadm02 oracle.SupportTools]# ./quorumdiskmgr --delete --device
[Success] Successfully deleted device /dev/exadata_quorum/QD_DATAC1_exa01dbadm01.
[Success] Successfully deleted device /dev/exadata_quorum/QD_DATAC1_exa01dbadm02.

Delete quorum disk target from node2.

[root@exa01dbadm02 oracle.SupportTools]# ./quorumdiskmgr --delete --target
[Success] Successfully removed target iqn.2015-05.com.oracle:qd--datac1--exa01dbadm02
[Success] Successfully removed backstore QD_DATAC1_exa01dbadm02
[Success] Successfully removed logical volume /dev/VGExaDb/LVDbVdexa01dbadm02DATAC1

Delete quorum disk configuration from node 2.

[root@exa01dbadm02 oracle.SupportTools]#  ./quorumdiskmgr --delete --config
[Success] Successfully deleted quorum disk configurations

[root@exa01dbadm02 oracle.SupportTools]#

At this point, we are done with removing the quorum disk configuration from our Exadata System, in next post, I would detail how we configure it in the system.

Hope it helps, thanks for reading, please subscribe to this blog to stay updated with latest news on Oracle Cloud Infrastructure and Oracle Autonomous Database Cloud Services and new articles.

Twitter : https://twitter.com/rajsoft8899

Linkedin : https://www.linkedin.com/in/raj-kumar-kushwaha-5a289219/

Facebook : https://www.facebook.com/rkushawaha

Tuesday, September 20, 2011

Controlfile is Missing

Database failed and you have restored it with the previous days backup and after restoring you noticed that control file is missing what do you do.

1. If one or more not all control file/s got deleted/corrupted you can replace it by the good one from another location. It is only hit and trial basis.

2. If you have backup of the control file you can restore it from the backup.

3. If none of these then create new control file.

What are the views available to see the information about export.

DBA_DATAPUMP_JOBS:

This view will show the active Data Pump jobs, their state, degree of parallelism, and the number of sessions attached.

DBA_DATAPUMP_SESSIONS:
This view gives the SADDR that assist in determining why a Data Pump session may be having problems. Join to the V$SESSION view for further information.

V$SESSION_LONGOPS:
This view helps determine how well a Data Pump export is doing. Basically gives you a progress indicator through the MESSAGE column.

How do you see how many instances are running?

For single instance Oracle Database Server, you can find the number of instances running using below commands.

In Linux, Unix the command:
$ ps -ef | grep pmon

In Windows:
services.msc

How to recover if we delete a data file at OS level no backup for that?

Bring the database to the mount state

SQL>alter database create datafile ;

SQL>recover datafile ;

SQL>alter database open;

DBA Interview Questions

1) Primary database scn is 22 and standby SCN is 24 how you will resolve this issue.

2) Archive log got deleted before shipped to standby location how you will resolve this issue.

3) 3 users running same select but one of them response time is 1hr and for other few minutes how u will diagnose this.

4) What is advantage of ASM over os storage and raw storage.

5) What is remastering in RAC

6) How you can see database version at OS level.

7) A job is running since long it was working fine earlier how you will check that How you will suggest joins to developer

9) 3 databases sizes 10gb, 100gb, 1TB how which database will take more time.

10) You lost control file database is using RMAN backup with nocatalog. If you loose whole db as well same time how you recover database.

11) what is sync, and async in standby how it works.

12) Shut immediate is taking too much time how you diagnose what is the issue.

13) How you take backup of OCR.

14) What will happen if voting disk is down.

15) What will happen if virtual IP is down in RAC.

VIP – Virtual IP address in RAC VIP is mainly used for fast connection in failover. Until 9i RAC faileover we used physical IP address of another server. When the connection request come from a client to server, then failure of first server listener then RAC redirect the connection request to second available server using physical IP address. Hence it is physical IP address rediretion to second physical IP address is possible only after we get timeout error from First Physical IP address. So connection should wait a while for getting TCP connection timeout. From RAC 10g we can use the VIP to save connection timeout wait, Because ONS (Oracle Notification Service) maintains communication between each nodes and listeners. Once ONS found any listener down or node down, it will notify another nodes and listeners. While new connection is trying to establish connection to failure node or listener, virtual IP of failure node automatically divert to surviving node. This Process will not wait for TCP/IP timeout event. So new connection will be faster even one listener/node failed.

RMAN Interview Questions

RMAN Interview Questions

1) If one archive deleted before applying on standby and you do not have backup how u resolve this issue?. Database size is in TB so recreating Standby is not good idea.

2) If block change tacking is enabled on production database will it be enabled on cloned database automatically?

3) You have assigned 3-4 channels in RMAN backup how you will identify whether all are utilized or not?

4) How you do performance tuning for RMANbackups?

5) Can we register manual cold backup in RMAN?

6) Can we recreate oracle inventory if we do not have any backup?

7) What is difference between image copy & normal backup in terms of performance?

8) 10K blocks in your database got corrupted how you will resolve this?

9) What is the benefit of Recovery Catalog and would you create one?

10) Can you register multiple target databases in a single RMAN Catalog?

11) When you try to register a target database in RMAN catalog then you get error that Database is already registered? What could be the reason of it and how would you overcome from this situation?

12) How would you take archivelog log backups?

13) What is the benefits of taking RMAN backups over other backup strategies?

Monday, September 19, 2011

Oracle Jobs Interview Questions and Answers

What is Log Switch? - The point at which ORACLE ends writing to one online redo log file and begins writing to another is called a log switch.
What is On-line Redo Log? - The On-line Redo Log is a set of tow or more on-line redo files that record all committed changes made to the database. Whenever a transaction is committed, the corresponding redo entries temporarily stores in redo log buffers of the SGA are written to an on-line redo log file by the background process LGWR. The on-line redo log files are used in cyclical fashion.
Which parameter specified in the DEFAULT STORAGE clause of CREATE TABLESPACE cannot be altered after creating the tablespace? - All the default storage parameters defined for the tablespace can be changed using the ALTER TABLESPACE command. When objects are created their INITIAL and MINEXTENS values cannot be changed.
What are the steps involved in Database Startup? - Start an instance, Mount the Database and Open the Database.
What are the steps involved in Instance Recovery? - Rolling forward to recover data that has not been recorded in data files, yet has been recorded in the on-line redo log, including the contents of rollback segments. Rolling back transactions that have been explicitly rolled back or have not been committed as indicated by the rollback segments regenerated in step a. Releasing any resources (locks) held by transactions in process at the time of the failure. Resolving any pending distributed transactions undergoing a two-phase commit at the time of the instance failure.
Can Full Consistent Backup be performed when the database is open? - No.
What are the different modes of mounting a Database with the Parallel Server? - Exclusive Mode If the first instance that mounts a database does so in exclusive mode, only that Instance can mount the database. Parallel Mode If the first instance that mounts a database is started in parallel mode, other instances that are started in parallel mode can also mount the database.
What are the advantages of operating a database in ARCHIVELOG mode over operating it in NO ARCHIVELOG mode? - Complete database recovery from disk failure is possible only in ARCHIVELOG mode. Online database backup is possible only in ARCHIVELOG mode.
What are the steps involved in Database Shutdown? - Close the Database, Dismount the Database and Shutdown the Instance.
What is Archived Redo Log? - Archived Redo Log consists of Redo Log files that have archived before being reused.
What is Restricted Mode of Instance Startup? - An instance can be started in (or later altered to be in) restricted mode so that when the database is open connections are limited only to those whose user accounts have been granted the RESTRICTED SESSION system privilege.
What is Partial Backup? - A Partial Backup is any operating system backup short of a full backup, taken while the database is open or shut down.
What is Mirrored on-line Redo Log? - A mirrored on-line redo log consists of copies of on-line redo log files physically located on separate disks, changes made to one member of the group are made to all members.
What is Full Backup? - A full backup is an operating system backup of all data files, on- line redo log files and control file that constitute ORACLE database and the parameter.
Can a View based on another View? - Yes.
Can a Tablespace hold objects from different Schemes? - Yes.
Can objects of the same Schema reside in different tablespaces? - Yes.
What is the use of Control File? - When an instance of an ORACLE database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery.
Do View contain Data? - Views do not contain or store data.
What are the Referential actions supported by FOREIGN KEY integrity constraint? - UPDATE and DELETE Restrict - A referential integrity rule that disallows the update or deletion of referenced data. DELETE Cascade - When a referenced row is deleted all associated dependent rows are deleted.
What are the type of Synonyms? - There are two types of Synonyms Private and Public
What is a Redo Log? - The set of Redo Log files YSDATE,UID,USER or USERENV SQL functions, or the pseudo columns LEVEL or ROWNUM.
What is an Index Segment? - Each Index has an Index segment that stores all of its data.
Explain the relationship among Database, Tablespace and Data file.? - Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace
What are the different type of Segments? - Data Segment, Index Segment, Rollback Segment and Temporary Segment.
What are Clusters? - Clusters are groups of one or more tables physically stores together to share common columns and are often used together.
What is an Integrity Constrains? - An integrity constraint is a declarative way to define a business rule for a column of a table.
What is an Index? - An Index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.
What is an Extent? - An Extent is a specific number of contiguous data blocks, obtained in a single allocation, and used to store a specific type of information.
What is a View? - A view is a virtual table. Every view has a Query attached to it. (The Query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)
What is Table? - A table is the basic unit of data storage in an ORACLE database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.
What is a Synonym? - A synonym is an alias for a table, view, sequence or program unit.
What is a Sequence? - A sequence generates a serial list of unique numbers for numerical columns of a database’s tables.
What is a Segment? - A segment is a set of extents allocated for a certain logical structure.
What is schema? - A schema is collection of database objects of a User.
Describe Referential Integrity? - A rule defined on a column (or set of columns) in one table that allows the insert or update of a row only if the value for the column or set of columns (the dependent value) matches a value in a column of a related table (the referenced value). It also specifies the type of data manipulation allowed on referenced data and the action to be performed on dependent data as a result of any action on referenced data.
What is Hash Cluster? - A row is stored in a hash cluster based on the result of applying a hash function to the row’s cluster key value. All rows with the same hash key value are stores together on disk.
What is a Private Synonyms? - A Private Synonyms can be accessed only by the owner.
What is Database Link? - A database link is a named object that describes a “path” from one database to another.
What is a Tablespace? - A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together
What is Rollback Segment? - A Database contains one or more Rollback Segments to temporarily store “undo” information.
What are the Characteristics of Data Files? - A data file can be associated with only one database. Once created a data file can’t change size. One or more data files form a logical unit of database storage called a tablespace.
How to define Data Block size? - A data block size is specified for each ORACLE database when the database is created. A database users and allocated free database space in ORACLE datablocks. Block size is specified in INIT.ORA file and can’t be changed latter.
What does a Control file Contain? - A Control file records the physical structure of the database. It contains the following information. Database Name Names and locations of a database’s files and redolog files. Time stamp of database creation.
What is difference between UNIQUE constraint and PRIMARY KEY constraint? - A column defined as UNIQUE can contain Nulls while a column defined as PRIMARY KEY can’t contain Nulls. 47.What is Index Cluster? - A Cluster with an index on the Cluster Key 48.When does a Transaction end? - When it is committed or Rollbacked.
What is the effect of setting the value “ALL_ROWS” for OPTIMIZER_GOAL parameter of the ALTER SESSION command? - What are the factors that affect OPTIMIZER in choosing an Optimization approach? - Answer The OPTIMIZER_MODE initialization parameter Statistics in the Data Dictionary the OPTIMIZER_GOAL parameter of the ALTER SESSION command hints in the statement.
What is the effect of setting the value “CHOOSE” for OPTIMIZER_GOAL, parameter of the ALTER SESSION Command? - The Optimizer chooses Cost_based approach and optimizes with the goal of best throughput if statistics for atleast one of the tables accessed by the SQL statement exist in the data dictionary. Otherwise the OPTIMIZER chooses RULE_based approach.
What is the function of Optimizer? - The goal of the optimizer is to choose the most efficient way to execute a SQL statement.
What is Execution Plan? - The combinations of the steps the optimizer chooses to execute a statement is called an execution plan.
What are the different approaches used by Optimizer in choosing an execution plan? - Rule-based and Cost-based.

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