Friday, December 16, 2011

Oracle RAC Interview Questions

Q-1 : What is the split-brain scenario?
A-1 : In Oracle RAC, split-brain is the scenario when one or more nodes updates to the database files w/o considering the integrity with other nodes. so in that scenario there is high possiblity of compromissing of database integrity and introducing the corruption to the database.

Q-2: What is the role of voting disk/file in RAC?
A-2: In Oracle RAC, voting disk file is used to determine the state of each nodes in the cluster. Each node should write heartbeat to the voting disk in predetermine interval i.e. 1 sec, so other nodes in the the cluster know that the node is alive. If node could not register the heartbeat to voting disk in stipulated time frame then it should be fence out from cluster to avoid split-brain scenario, which might introduce corruption to the database. Oracle Cluster Synchronization Service Daemon(OCSSD) is responsible to maintain synchronization of the cluster using voting disk.

Q-3: History of RAC and main components of RAC?
A-3: Please refer article  Oracle Real Application Clusters (RAC) and main Components of RAC.

Q-4: Please describe the Oracle Clusterware startup sequence?
A-4: Please refer blog -  Oracle Clusterware Startup Sequence

Q-5:  Describe method to apply Patch on RAC database.
A-5: Please refer blog - Steps to apply GI and RDBMS patch to Oracle Grid & RDBMS home and database

Q-6: How to restore Oracle Local Registry ?
A-6: Please refer article : How to restore local OLR in Oracle 11gR2 RAC?

Monday, February 7, 2011

How to restore local OLR in Oracle 11gR2 RAC?

When you see the following Error: PROCL-26OHAS00106 in your OHSD log file under $CRS_HOME/cdata/

2009-10-16 15:02:43.664: [ default][3046311632] OHASD Daemon Starting. Command string :restart2009-10-16 15:02:43.668: [ default][3046311632] Initializing OLR2009-10-16 15:02:43.672: [ OCROSD][3046311632]utopen:6m':failed in stat OCR file/disk /u01/app/11.2.0/grid/cdata/server1.olr, errno=2, os err string=No such file or directory2009-10-16 15:02:43.672: [ OCROSD][3046311632]utopen:7:failed to open any OCR file/disk, errno=2, os err string=No such file or directory2009-10-16 15:02:43.673: [ OCRRAW][3046311632]proprinit: Could not open raw device2009-10-16 15:02:43.673: [ OCRAPI][3046311632]a_init:16!: Backend init unsuccessful : [26]2009-10-16 15:02:43.673: [ CRSOCR][3046311632] OCR context init failure. Error: PROCL-26: Error while accessing the physical storage Operating System error [No such file or directory] [2]2009-10-16 15:02:43.673: [ default][3046311632] OLR initalization failured, rc=262009-10-16 15:02:43.674: [ default][3046311632]Created alert : (:OHAS00106:) : Failed to initialize Oracle Local Registry2009-10-16 15:02:43.674: [ default][3046311632][PANIC] OHASD exiting; Could not init OLR2009-10-16 15:02:43.674: [ default][3046311632] Done.

cd /oracle_crs/product/11.2.0/crs_1/cdata
touch lkcme25070.olr
cd /oracle_crs/product/11.2.0/crs_1/bin
./ocrconfig -local –restore /oracle_crs/product/11.2.0/crs_1/cdata/lkcme25070/backup_20101130_154551.olr