Logging from multiple apps/processes to a single log file

Question

Our app servers (weblogic) all use log4j to log to the same file on a network share. On top of this we have all web apps in a managed server logging errors to a common error.log. I can't imagine this is a good idea but wanted to hear from some pros. I know that each web app has its own classloader, so any thread synchronization only occurs within the app. So what happens when multiple processes start converging on a single log file? Can we expect interspersed log statements? Performance problems? What about multiple web apps logging to a common log file? The environment is Solaris.

Answer 1

In prudent mode logback will safely handle multiple JVMs possibly on different hosts writing to the same network-shared file. It can even deal with temporary network failures. Performance should be quite acceptable for few nodes, say 4 or less. For 5 or more nodes all logging heavily you may notice a performance hit.

Answer 2

This is generaly bad idea to have not synchronized write access to a file and certainly bad programming practice. The only case it might work is an append to a file on local machine - everybody just adds lines at the end of file.

But, since your file is on the network share, it will probably quickly turn into garbage. You didn't tell which distributed filesystem you are using, but for NFS you can find following explanation on open(2) man page:

O_APPEND The file is opened in append mode. Before each write(), the file offset is positioned at the end of the file, as if with lseek(). O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once. This is because NFS does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.

Of course this is C, but since Java is implemented in C it cannot do any better than that (at least not with regard to system calls:-)).

Answer 3

We have a requirement where we need to produce a single file from all the managed server running the same application . we developed a java logging server which opens ups a port and listen for log event. we used the log4j socket appender to write log event to the same port and created a single file.