Log is a critical part of an application. It serves as an eye to the programmer on how the application is working while debugging. Especially for applications running on production environment, if the application encounters problem and the problem cannot be reproduced on other environments, log will be extremely useful.While log is essential, but developers have to log smartly. Because if don't put log smartly, you may not get what you want while debugging or you may get too many redundant logs which eat up the disk space and degrade the performance of the system.So what and wha...

After installing MySQL, when we try to start MySQL, sometimes we may not be able to start it. The reasons can be different. We share some general cases where MySQL cannot be started.Case 1: Directory or file permission issueIf the permission is set wrongly in MySQL's $datadir and its sub directories or files, MySQL will not be able to read and write files normally.Error message:mysqld_safe Starting mysqld daemon with databases from /usr/local/mysql/data/usr/local/mysql/bin/mysqld_safe: line 107: /usr/local/mysql/data/imysql.local.err: Permission deniedCase 2: Port conflictThere may be other my...

Due to network, browser and cache issues, the JS executed in production may produce different results from the testing environments. Sometimes they may produce exceptions. Front-end developers may encounter this kind of exceptions frequently. But how to log and use them is seldomly considered by them. Actually, exception handling includes two steps : log and use.1. LogRegarding to log error, this is relatively convenient, since in each browser, there is one interface called window.onerror.window.onerror =function(errorMessage, scriptURL, lineNumber){ alert(errorMessage, scriptURL, lineNumber)...

Usually, The purposes of log are for troubleshooting and displaying program running status. Good log will help us locate the error easier. Many programmers think log in programs is very simple, but it's not an easy task to write log codes to efficiently locate the error. Here we discuss about program log in three aspects:Where to logWhat to logLog styles to be avoidedWhere to log1. When calling external functionsWhen your program is calling some external functions which are not written by you, you need to log before and after the external function call. This will help debug.1. LOG.debug("Call...