log_innodb_status is not safe

[osheroff]

Hi,
(btw, this is the issue Simon Winstow was talking about)
I don't know if you'd want to use this code or work out another fix, but deadlock_retry can actually quite dangerous in a limited set of circumstances, due to the attempt to execute "SHOW INNODB STATUS". Here's what happens:

• transaction deadlocks
• call to log_innodb_status is made
• SHOW INNODB STATUS command fails, for a variety of reasons -- including that the user doesn't have permission to execute this command.
• the "rescue Exception" block kicks in, but mysql has already silently rolled-back our transaction because of the error in SHOW INNODB STATUS.
• the transaction continues, but is fundamentally broken and we've silently lost data.

[mperham]

I suggest you try to run the command at startup and en/disable based on whether it works. This way the user need do nothing to get the logging if permissions are ok. don't clutter up the code with configuration; just print out a warning if perms are wrong.

[osheroff]

Ok, try that on for size -- before we run the first transaction we're asked to run we'll check and see if "show innodb status" crashes.