Avoiding Logon Storm (DoS) on Oracle Database

A Logon storm is a sudden spike in the number of client connection requests. Logon storms can occur due to a variety of factors. They could be malicious like a DoS attack. Or they could occur due to administrative actions – such as a middle tier coming online.

Configuring Database Resident Connection Pooling (DRCP)

Database Resident Connection Pooling (DRCP) provides a connection pool in the database server for typical Web application usage scenarios where the application acquires a database connection, works on it for a relatively short duration, and then releases it. DRCP pools "dedicated" servers. A pooled server is the equivalent of a server foreground process and a database session combined.

Clusterware resource ora.cvu

ora.cvu is a new resource introduced with Grid Infrastructure 11.2.0.2. The purpose of this resource is to invoke clusterware health checks at regular intervals. It is a singleton resource with cardinality of 1 and invokes the cluster verification utility. It executes the following command in the background.

Configuring Resource Manager for Multiple Workloads

Resource Manager can be configured to manage workloads (OLTP,DSS etc) differently by configuring consumer groups and resource plans.

Consumer Group:

A consumer group is a collection of sessions that are managed as a unit. You can define consumer groups for each application in your database. Or you can define consumer groups for each type of workload, e.g. OLTP, reports, maintenance, etc.

Resource Manager and Instance Caging

Brief: Excessive CPU load can destabilize the server and expose operating system bugs and can also prevent critical Oracle background processes from running in a timely manner,  resulting in failures such as database instance evictions on a RAC database.

Using Oracle Database Resource Manager, you can ensure that your database’s CPU  load is always healthy, thus avoiding all of these problems.

Recovering/Opening database for which archive log is missing

Some times you don't have the missing archivelogs and database cannot be opened due to it.

After incomplete recover we tried to open database with resetlogs but it failed, one hidden parameter (_ALLOW_RESETLOGS_CORRUPTION=TRUE) can be used to open database even though it’s not properly recovered.

Exadata: Knowing a bit Exadata administrative utilities

MegaCLI: This Utility (run as root on cell)  generate diagnostics or configuration information about your MegaRAID-controlled disk devices on an Exadata Storage Server or Compute Server. There are various command line options for this utility:

Exadata: Diagnostics using sundiag/deaddisk

For Sun Oracle Exadata Environments
On each Exadata compute and storage cell nodes, Oracle delivers a utility called sundiag.sh . Bydefault sundiag.sh script isinstalled in /opt/oracle.SupportTools.When logging Oracle Service Requests, it is common for Oracle Support to request the output of the sundiag.sh utility.

Exadata: Health Checking Exadata (Exachk)

Oracle’s exachk utility (NON-INTRUSIVE and does not change anything in the environment) is designed to perform a comprehensive health check of Exadata Database Machine. It is designed to audit important configuration settings within an Oracle Exadata Database Machine. The components examined are database servers, storage Servers, InfiniBand fabric, InfiniBand Switches, and Ethernet network.

exachk should be executed (under Oracle Software owner on DB node) after the initial Oracle Exadata Database Machine deployment, as part of the routine maintenance schedule (at least monthly), and before and after any system configuration change. You should run only one exachk instance at a time.

Exadata: Understanding key OS Processes for a cell

Exadata' s unique software runs different processes on OS to perform different functions. There are three main programs that run on the Exadata Storage Servers to facilitate cell operations cellsrv, MS and RS.  You can identify the OS processes by using ps.

Exadata: What differentiates GI on Exadata with GI on non-Exadata?

The installation,configuration, and administration of Grid Infrastructure on Exadata is identical to Grid Infrastructure on non-Exadata systems. On Exadata, Oracle has elected to store the Oracle Cluster Registry (OCR) and voting disks on Oracle ASM disk groups, mapped to Exadata storage server grid disks. Most processes in Exadata’s Oracle 11gR2 Grid infrastructure perform the same functions as non-Exadata 11gR2 installations, but one software component that plays a special role in Exadata environments is the diskmon process and associated processes

Exadata: Get Cell statistics quickly

Some time you want to get the quick information about Cell like offloading, Storage index etc. Exadata cell has a small tool named as cellsrvstat which provides the comprehensive information like below

Exadata: Replacing damaged disk is really plugNplay activity

On Exadata if any disk is failed due to some problem , replacing it will not be the hard job. It is quite simple task. On my testing environment I did the below to test it, things are quite self explanatory.

Exadata: Monitoring Active Requests, Alerts and Wait Events

Active request provides a client-centric or application-centric view of client I/O requests that are currently being processed by a cell. An active request is characterized at all levels: instance, database, ASM, and cell.

Alerts represent events of importance occurring within the storage cell, typically indicating that storage cell functionality is either compromised or in danger of failure.An alert is automatically triggered when a predefined hardware or software issue is detected, or when a metric exceeds a threshold.

Alert history entries are retained for a maximum of 100 days. If the number of alert history entries exceeds 500, then the alert history entries are only retained for 7 days. 

Stateful alerts represent observable cell states that can be subsequently retested to detect whether the state has changed, indicating that a previously observed alert condition is no longer a problem.
Stateless alerts represent point-in-time events that do not represent a persistent condition; they simply show that something has occurred.

Exadata: Monitoring Performance (Using Metrics)

Like database  in Exadata Metrics and alerts also help you monitor Oracle Exadata Storage Server Software. Metrics are associated with objects such as cells and cell disks, and can be cumulative, rate, or instantaneous.
Metrics are recorded observations of important run-time properties, retained in memory and stored on a disk for a more permanent history.

Exadata: Implementing Cell Security

Security for Exadata Cell is enforced by identifying which clients can access cells and grid disks. Clients include Oracle ASM instances, database instances, and clusters. By default Exadata allows all ASM clusters and databases in the system access to all grid disks. You can implement cell security control access to grid disks at two levels, by ASM cluster and by database

Privileges required for Debugging Oracle Procedure

The following privileges are required for debugger:
1. GRANT ALTER SESSION TO user_name;
2. GRANT CREATE SESSION TO user_name;
3. GRANT EXECUTE ON DBMS_DEBUG to user_name;


Minimum requirements to debug other than your own procedures, functions, and packages:
1. GRANT ALTER ANY PROCEDURE TO user_name; (compile)
2. GRANT CREATE ANY PROCEDURE TO user_name; (edit / save)


The following additional privileges are required for debugger inversion 10g and any version released after that:1. GRANT DEBUG ANY PROCEDURE TO user_name;
2. GRANT DEBUG CONNECT SESSION TO user_name;

Building DR site (RAC 11gR2) using EMC's SRDF/A (Windows 2008R2)

Overview:

Symmetrix Remote Data Facility (SRDF) is a Symmetric based business continuance and disaster restart solution. In simple terms, SRDF is a configuration of multiple Symmetrix units whose purpose is to maintain real time copies of logical data volume in more than one location. The Symmetrix unit can be in the same room, in different building in the same campus or hundreds of miles apart. 

Column with NVARCHAR(4000) not appearing in Resultset using DG4MSQL

Problem:
On SQL Server side a table had a column (desc_details) with NVARCHAR(4000), DG4MSQL has been configured for communication with SQL Server. Querying to that table was not showing the column (desc_details) but all other columns were being shown correctly.

12c: Database Resident Connection Pooling

Database Resident Connection Pooling (DRCP) provides a connection pool in the database server for typical Web application usage scenarios. It complements middle-tier connection pools that share connections between threads in a middle-tier process. DRCP is relevant for architectures with multi-process single threaded application servers (such as PHP/Apache) that cannot perform middle-tier connection pooling. DRCP is available to clients that use the OCI driver with C, C++, and PHP.