How to know when there's too much logging messages?

How to know when is too much logging? When you know that the logged information isn't important in the long term, being for debug actions or bug correction, or the application doesn't deal with too much important information.

Sometimes you need to log almost everything. Is performance or full possibility of analysis the most important part of an application? It really depends.

I've worked in the past with some integration with a lot of different webservices, like 10 in a same app. We logged all xml requests and responses. Is this an overhead? In the long term, I don't think so because we worked with a lot of credit card operations and should have every process made with the server logged. How to know what happened when there was a bug?

You wouldn't believe what I've saw in some of the xml responses. I've even received a xml without closing tags, from a BIG airplane company. Were the "excessive logs" a bad practice? Say that to your clients when you have to prove that the error came from the other vendor.

Most logging libraries incorporate a means to confirm that logging is enabled before processing an instruction:

For example:

public void foo(ComplicatedObject bar) {
    Logger.getInstance(Foo.class).trace("Entering foo(" + bar + ")");
}

Could be quite costly depending on the efficiency of the bar.toString() method. However, if you instead wrap that in a check for the logging level before doing the string concatenation:

static {
    Logger log = Logger.getInstance(Foo.class);

public void foo(ComplicatedObject bar) {
    if (log.isTraceEnabled()) {
        log.trace("Entering foo(" + bar + ")");
    }
}

Then the string concatenation only occurs if at least one appender for the class is set to Trace. Any complicated log message should do this to avoid unnecessary String creation.

Ideally, you use a logger that allows logging levels; log4j has fatal/error/warn/debug/info, for example. That way, if you set the level to "only show errors", you don't lose speed to the software building log messages you didn't need.

That said, it's only too much logging until you wind up needing something that would have been logged. It sounds like most of the logging that's slowing you down should be "trace" level, though; it's showing you what a profiler would have.