Name

trace

Synopsis

DBI->trace($trace_level)
DBI->trace($trace_level, $trace_filename)

DBI trace information can be enabled for all handles using the trace DBI class method. To enable trace information for a specific handle, use the similar $h->trace method described elsewhere.

Trace levels are as follows:

0

Trace disabled.

1

Trace DBI method calls returning with results or errors.

2

Trace method entry with parameters and returning with results.

3

As above, adding some high-level information from the driver and some internal information from the DBI.

4

As above, adding more detailed information from the driver. Also includes DBI mutex information when using threaded Perl.

5 and above

As above, but with more and more obscure information.

Trace level 1 is best for a simple overview of what’s happening. Trace level 2 is a good choice for general purpose tracing. Levels 3 and above (up to 9) are best reserved for investigating a specific problem, when you need to see “inside” the driver and DBI.

The trace output is detailed and typically very useful. Much of the trace output is formatted using the neat function, so strings may be edited and truncated.

Initially, trace output is written to STDERR. If $trace_filename is specified, the file is opened in append mode and all trace output (including that from other handles) is redirected to that file. Further calls to trace without a $trace_filename do not alter where the trace output is sent. If $trace_filename is undefined, then trace output is sent to STDERR and the previous trace file is closed.

See also the $h->trace and $h->trace_msg methods for information about the DBI_TRACE environment variable.