= Debugging server components =

A grab-bag of techniques for debugging BOINC server software:

== Log files ==

Most error conditions are reported in the log files. Make sure you know where these are. If you're interested in the history of a particular WU or result, grep for `WU#12345` or `RESULT#12345` (where 12345 represents the ID) in the log files. The [HtmlOps html/ops pages] also provide an interface for this.

== Debugging the scheduler ==

The scheduler is a CGI program;
it reads a request from stdin and writes a reply to stdout.
You can run it with a command-line debugger like `gdb`:
 * Copy the "scheduler_request_X.xml" file from a client to the machine running the scheduler. (X = your project URL)
 * Run the scheduler under the debugger, giving it this file as stdin, i.e.:
{{{
gdb cgi
(set a breakpoint)
r < scheduler_request_X.xml
}}}
 * You may have to doctor the database as follows to keep the scheduler from rejecting the request:
{{{
update host set rpc_seqno=0, rpc_time=0 where hostid=N
}}}

This is useful for figuring out why your project is generating 'no work available' messages.  As an alternative to this, edit `handle_request.C`, and put a call to `debug_sched(sreq, sreply, "../debug_sched")` just before `sreply.write(fout)`. Then, after recompiling, touch a file called 'debug_sched' in the project root directory. This will cause transcripts of all subsequent scheduler requests and replies to be written to the `cgi-bin/` directory with separate small files for each request.  The file names are `sched_request_H_R` where H=hostid and R=rpc sequence number. This can be turned off by deleting the 'debug_sched' file.

To get core files for scheduler crashes, put the following line in sched/main.C, and recompile:
{{{
#define DUMP_CORE_ON_SEGV 1
}}}

== MySQL interfaces ==

You should become familiar with MySQL tools such as
 * The [http://dev.mysql.com/doc/refman/5.0/en/mysql.html mysql interpreter] and in particular the '[http://dev.mysql.com/doc/refman/5.0/en/show-processlist.html show processlist;]' query.
 * [http://jeremy.zawodny.com/mysql/mytop/ mytop]: like 'top' for MySQL
 * [http://www.phpmyadmin.net/ phpMyAdmin]: general-purpose web interface to MySQL

== Database query tracing ==

If you uncomment the symbol `SHOW_QUERIES` in db/db_base.C, and recompile everything, all database queries will be written to stderr (for daemons, this goes to log files; for command-line apps it's written to your terminal). This is verbose but extremely useful for tracking down database-level problems.