Thursday, September 17, 2015

Error: OSWatcher uses the OS utility Logman to gather its data

Starting Operating System Watcher for Windows (OSWatcher) may return following error message.
c:\oswfw_2_5.1\oswfw_2_5.1>oswatcher 20 120

OSWatcher uses the OS utility Logman to gather its data.

Monday, September 14, 2015

TNS-12531: TNS:cannot allocate memory

I found this message in my listener.ora file while investigating a ORA-00600 error which was causing the database to slow down very much.
24-FEB-2015 11:55:00 * 12531
TNS-12531: TNS:cannot allocate memory

Tuesday, September 1, 2015

TNS-12560: TNS:protocol adapter error

This is one of the most common and generic errors you may face while trying to connect with the database. There could be a lot of reasons for this. To troubleshoot this, you may want to go through following checklist
Check your TNS entry in TNSNAMES.ORA file, if it is set correctly and there is no syntax error and it is pointing to correct server and instance

Tuesday, August 25, 2015

ORA-24247: network access denied by access control list (ACL)

This error message means that no access control list has been assigned to the host you (your application) are trying to access, or no required privileges have been granted to the user by adding user to the ACL. Following is an example executed on 12c ( to show how we create ACL and how to test it.  

Monday, August 17, 2015


Before 12c, there was no hard limit to restrict PGA memory usage by an Oracle session. It means that if a session keeps growing in memory, it would eventually allocate all available memory which would lead to a system slowness/hang and eventually system crash, I have discussed this scenario here.

Monday, August 10, 2015

Generating Bulk of Data for Testing Purpose

Sometimes we need to generate a huge amount of data to perform some testing. Type of data to be generated depends on the scenario you want to test. I will show here a very simple example to create a very huge table. I usually use it if I need to have a huge tablespace or table to perform some test. For example, to test backup

Tuesday, August 4, 2015

Changing AWR Snapshot Retention and Interval

By default AWR snapshot interval is set to 60 minutes and retention of snapshots is set to 8 days. For better and precise investigation of problems, I recommend to use an interval of 15 minutes and retention of 35 days. If database is huge in size and operations, also RAC, your SYSAUX tablspace would certainly grow in size with these settings. I have observed size of SYSAUX tablespace for a 3 nodes RAC database, around 14G with aforementioned settings.

Monday, August 3, 2015

Oracle Deferred Segment Creation

Starting 11g Release 2, we can create a table/index/LOB without space allocated to it (no segment creation) until first row is inserted into the table. Init parameter DEFERRED_SEGMENT_CREATION is used to setup the default behavior. By default value of this parameter is set to TRUE, which means that whenever a table will be created,

Tuesday, July 28, 2015

Checkpoint not Complete

This is one of the most common messages a DBA could see in alert log file of a database. Exact message should be similar to the following
Wed Mar 04 12:02:01 2015
Thread 1 cannot allocate new log, sequence 201
Checkpoint not complete

Thursday, July 23, 2015

Finding Sessions with High CPU Usage

If database server CPU usage is showing 100%, or high 90%, DBA needs to find out which session is hogging the CPU(s) and take appropriate action. I will explain in the following that how can we find out the session(s) which are excessively using CPU.

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