Obtaining a DB2 trace using db2trc

 

The db2trc command controls the trace facility provided with DB2®. The trace facility records information about operations and formats this information into a readable form.

Keep in mind that there is added overhead when a trace is running so enabling the trace facility might impact your system's performance.

In general, DB2 Support and development teams use DB2 traces for troubleshooting. You might run a trace to gain information about a problem that you are investigating, but its use is rather limited without knowledge of the DB2 source code.

Nonetheless, it is important to know how to correctly turn on tracing and how to dump trace files, just in case you are asked to obtain them.

Note: You will need one of SYSADM, SYSCTRL or SYSMAINT authority to use db2trc To get a general idea of the options available, execute the db2trc command without any parameters: 

C:\>db2trc 
Usage: db2trc (chg|clr|dmp|flw|fmt|inf|off|on) options
For more information about a specific db2trc command parameter, use the -u option. For example, to see more information about turning the trace on, execute the following command: 

db2trc on -u
This will provide information about all of the additional options (labeled as "facilities") that can be specified when turning on a DB2 trace.

When turning trace on, the most important option is -L. This specifies the size of the memory buffer that will be used to store the information being traced. The buffer size can be specified in either bytes or megabytes. (To specify megabytes append either "M" or "m" after the value). The trace buffer size must be a power of two megabytes. If you specify a size that does not meet this requirement, the buffer size will automatically be rounded down to the nearest power of two.

If the buffer is too small, information might be lost. By default only the most recent trace information is kept if the buffer becomes full. If the buffer is too large, it might be difficult to send the file to the DB2 support team.

If tracing an operation that is relatively short (such as a database connection), a size of approximately 8MB is usually sufficient: 

C:\> db2trc on -l 8M 
Trace is turned on

However, if you are tracing a larger operation or if a lot of work is going on at the same time, a larger trace buffer might be required.

On most platforms, tracing can be turned on at any time and works as described above. However, there are certain situations to be aware of:

  1. On multiple database partition systems, run a trace for each physical (as opposed to logical) database partition.

  2. On HP-UX, Linux™ and Solaris platforms, if the trace is turned off after the instance has been started, a very small buffer will be used the next time the trace is started regardless of the size specified. For example, yesterday you turned trace on by using db2trc on -l 8m, then collected a trace, and then turned the trace off (db2trc off). Today you wish to run a trace with the memory buffer set for 32 megabytes (db2trc on -l 32m) without bringing the instance down and restarting. You will find that in this case trace will only get a small buffer. To effectively run a trace on these platforms, turn the trace on before starting the instance with the size buffer you need and "clear" the buffer as necessary afterwards.

Parent topic: Basic trace diagnostics

Related reference
db2trc - Trace command