ORA-00845: MEMORY_TARGET not supported on this system

If we face ORA-00845 during database startup, it would mean that /dev/shm file system is not configured with appropriate value required to start the database instance. We need to mount /dev/shm with a value that should be equal or more than the value of memory we want to allocate to all instances/SGAs (ASM as well as database instances) that would run on this host.

You may find following type of warning in alert log file.

Slow RMAN Performance for CROSSCHECK and DELETE OBSOLETE

I faced an issue recently where my CROSSCHECK and DELETE OBSOLETE commands were too much slow to execute, actually these were hung. The reason for this issue was IP address change of my NFS server form where a drive was mounted on database server for backups and backups were being taken on this NFS share. After NFS server’s IP address change, RMAN would go to check old IP address to search for the old/obsolete backups when we executed CROSSCHECK and DELETE OBSOLETE commands.

ORA-01586: database must be mounted EXCLUSIVE and not open for this operation

As this message clearly explains, this error means that the operation you are going to perform that returned this error, needs database to be mounted EXCLUSIVELY - by only one instance. In my case, I was trying to drop a RAC database when I faced ORA-01586. I realized that the other instance of my RAC database is still up and it is needed that all the instances of a RAC database should be down before we can drop a database.

CRS-4700: The Cluster Time Synchronization Service is in Observer mode

This is very important to keep the time of cluster nodes synchronized across the cluster. Time difference among nodes can cause issues, and sometime it can cause the node(s) restart.

There are 2 ways of keeping the time synchronized across the RAC nodes: using NTP at OS level, or using Cluster Time Synchronization Service that runs as a RAC resource.

Segment Space Growth History and Forecast

I have already written articles to get tablespace space usage history and forecast (10g and 11g, 12c and above) and database space usage history and forecast (10g and 11g, 12c and above). Here, I will explain how we can get the same information about segments, and can forecast the future growth of segments.

ORA-39510 While Starting Cluster Health Monitor Repository (MGMTDB)

MGMTDB, also called Management Repository Database was introduced in 12c Grid Infrastructure. This repository database is used to store Cluster Health Monitor data so that this monitoring data can be used for Grid Infrastructure troubleshooting. This database resource is set to start automatically on the start of Grid Infrastructure, but, there could be some scenarios where MGMTDB might not start because of some issues. One of the similar problems I face because of which MGMTDB could not start automatically. When I tried to start Management Repository Database manually, it failed to start and threw following error messages.

ORA-00313 ORA-00312 ORA-17503 ORA-15173 in Standby Alert Log File

Errors in file /u01/app/oracle/diag/rdbms/standby_db/standby_db/trace/standby_db_lgwr_393229.trc: ORA-00313: open failed for members of log group 12 of thread 2 ORA-00312: online log 12 thread 2: '+FRA_DG/standby_db/redolog12_02.rdo' ORA-17503: ksfdopn:2 Failed to open file +FRA_DG/standby_db /redolog12_02.rdo

Creating a Real Application Cluster(RAC) 12c database using DBCA

After installing Oracle RAC, next step is to create a RAC database. Following is the process of creating a RAC database using dbca. Same method works on Windows or Unix based platforms.To invoke dbca, open a command line and run command “dbca”. On Windows, DBCA can also be invoked from Program Menu..

Oracle Flex Cluster

Oracle Real Application Cluster is a feature that was first introduced in Oracle 9i (Oracle Parallel Servers was a similar feature available before 9i, but not as robust as RAC) and has been an essential part of Oracle’s Maximum Availability Architecture. Since its advent in Oracle 9i, it has evolved a lot. Oracle 9i onward, every new release of Oracle has introduced something new in RAC which made it even more resilient, fault tolerant, and easy to manage architecture.

    

Oracle Flex ASM

Starting 12c, Oracle has introduced two very interesting features to add up to MAA (Maximum Availability Architecture), Oracle Flex Cluster and Oracle Flex ASM. In this article I will be explaining and demonstrating about Oracle flex ASM.

In flex ASM, you don’t need ASM instance to be running on each node (the Hub Node) because database instance can communicate with some other ASM instance running on any other node in the cluster.