# Friday, 07 July 2006

Conditional breakpoints were another really important tool in solving a recent "only happens at the big installations" bug in a big and complicated C++ application. We wanted to debug the code with as few rebuilds as possible and we really didn't know how parts of it worked at all. Tracepoints helped us to figure out a lot of it in a short time. We didn't have a decent repro case though, so here's what we did:

  • created a script to add an audit table and some triggers that write to it
  • created a script to remove those triggers and the table
  • created a batch file to run a server in verbose mode, and redirect the output to a text file (remembering DOS commands sure can be helpful...   myapp.exe -verbose >logfile.txt was the magic phrase.)
  • wrote some instructions for the support guy to grab a backup of the database, run the first script, run the batch file, let it run all night, then in the morning grab another backup of the database, run the second script, and stop the batch file.

Now we ran some queries on the morning version of the database to confirm that at least one X was missing a Y that should have been calculated overnight. We even had the Xid. Thanks to the tracepoint work of the previous day we knew where to be suspicious. A little digging in the trigger output told us whether the problem was "didn't get added" or "got added, but then got deleted". The last step was conditional breakpoints. These let us say "only stop here when you're processing the X with this Xid."

This really saves time when you just need to drill into what's happening in the case that is going wrong. You get to it by right clicking the red dot or diamond and choosing Condition.


Friday, 07 July 2006 16:35:26 (Eastern Daylight Time, UTC-04:00)  #    Comments [0]
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