Update: After finding a reference to problems with BSDI and the realpath() system call in the mailing list archives, I tried rebuilding MySQL with the HAVE_BROKEN_REALPATH flag defined. That seemed to clear up the problem, at least with the testing that I performed. YMMV.
DSC _________________________________________________________________________ Dan S. Camper Borrowed Time, Inc. Software Thaumaturge http://www.bti.net ------ Forwarded Message > From: Dan S. Camper <[EMAIL PROTECTED]> > Date: Thu, 18 Apr 2002 12:41:31 -0500 > To: MySQL <[EMAIL PROTECTED]> > Subject: BSD: Random unknown database error > > All: > > Recently I've run into a problem where I intermittently receive an "Unknown > database" error while attempting to communicate with a local MySQL server. I > read through the mail list archives and discovered that others reported > similar problems under BSD, but I didn't see any concrete solutions. I may > not be able to provide a solution, but I believe I can pinpoint the cause. > > Let me apologize now for the length of this message. I'm trying to explain > enough so that someone else, more knowledgable about MySQL's internals, can > either use it to solve the problem or refute my guess. > > First, my environment: MacOS X (10.1.4), MySQL 3.23.49, running on a G3 > PowerBook (Firewire), latest dev tools from Apple. The MySQL server is > running on that system as well as my own C++ code. > > Before seeing the problem within MySQL I found a problem with my own > multithreaded code. Each thread is responsible for loading a file in one > directory and then manipulating a couple of other files in a different > directory, all referenced relatively to the application's directory. When the > load got high -- there were many concurrent threads -- I would intermittently > receive an error from the OS telling me that one of the files I was trying to > open could not be found. Given that the file in question was one that was > supposed to always be present, I grew suspicious. After a bit of debugging, > imagine my surprise when I discovered that the full pathname the OS was trying > to use was wrong. Example > > Source file: foo/text.txt > Dest file: data/index.txt > App directory: /Users/lordgrey/Projects/myproject/ > > When the problem occurred while opening the dest file, referenced relatively, > the OS was actually trying to open: > > /Users/lordgrey/Projects/myproject/foo/data/index.txt > > instead of > > /Users/lordgrey/Projects/myproject/data/index.txt > > Once I nailed down a variable with the current working directory at > application launch time and used that to fully qualify my datafiles, all of my > problems disappeared. > > As further testing, I started cranking up the number of threads. Now, in > addition to dinking around with files, each thread has its own MySQL > connection. Increasing the number of threads started causing the "unknown > database" error to appear, pretty much in direct proportion to the number > threads. > > The other problem reports in the archive noted that the "unknown database" > problem seemed to occur when the system's load was high. That would agree > with what I found. > > Anyway, it occurs to me that MySQL is failing to find a database -- which is a > directory -- for the same reason that my code couldn't find its own data > files. Namely: MySQL is using a relative path, BSD is mucking around with > the concept of "current working directory" incorrectly and it's colliding with > other concurrent threads also trying to use relative paths. > > I haven't picked the MySQL source code apart to see if this is really the case > or not, but it seems reasonable. If it's true then the actual problem lies in > BSD/MacOS/etc. but it can be worked around in the MySQL server. > > Cheers, > > DSC ------ End of Forwarded Message --------------------------------------------------------------------- Before posting, please check: http://www.mysql.com/manual.php (the manual) http://lists.mysql.com/ (the list archive) To request this thread, e-mail <[EMAIL PROTECTED]> To unsubscribe, e-mail <[EMAIL PROTECTED]> Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
