Common Issues and Troubleshooting
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Setting the isolation level failed with ERROR 1568 (25001): Transaction characteristics can't be changed while a transaction is in progress. A transaction's isolation level is decided before it starts, so this one's a question of order.
ERROR 3572 (HY000): Statement aborted because lock(s) could not be acquired immediately and NOWAIT is set isn't really a failure. You asked MySQL not to wait for a locked row, and the row was locked. The fix is deciding what your code does in that case.
Looking at MySQL's locks failed with ERROR 1142 (42000): SELECT command denied to user 'inventory_app'@'localhost' for table 'data_locks'. The table's fine, and so is the account: it just has no rights outside its own database. Here's the fix, on a separate account, so the application's account stays as it is.
Changing a MySQL setting failed with ERROR 1227 (42000): Access denied; you need (at least one of) the SUPER or SYSTEM_VARIABLES_ADMIN privilege(s) for this operation. The word GLOBAL in the statement is the cause. Most of the time you don't want the whole server changed anyway, and one word fixes it.
I wanted to see which transactions were open, and MySQL said ERROR 1227 (42000): Access denied; you need (at least one of) the PROCESS privilege(s) for this operation. The account has full rights on its own database, and that's not enough. Here's why, and the right way to fix it without making your application's account more powerful.
An UPDATE hung for a while, then failed with ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction. Raising the timeout is the tempting fix, and the wrong one, because the real problem is another transaction holding the row. Here's how to find it, and a surprise about what the error leaves behind.
An ordinary UPDATE failed with ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction, and MySQL threw away everything the transaction had done so far. Two transactions had taken the same rows in opposite orders. Here's how to see that for yourself, and the small change that stops it.
curl http://localhost:5190/demo/enum?status=placed and grep -rn 'class' src --include=*.cs both failed with zsh: no matches found, and neither program ever ran. Commands like these work in bash, and they appear that way in a lot of tutorials. In zsh, you have to quote them.
My script fed commands to a program through a named pipe. It closed the pipe when it was done, and waited for the program to finish, and that wait never ended. Another process had a copy of the pipe open, and I'd given it that copy without noticing.
I stopped my API with pkill -f, and a long script in another terminal died too, with exit code 143 and no error message. The script wasn't the API. It only had the API's name somewhere in its command line, and that's all -f needs.
