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Kernel Logging Rules

Kernel Logging Rules¶

Basic Rules¶

cout/cerr should never be used
- except early in process startup before the log() system is initialized
  
  For such cases, it would be good to use cerr, but right now there is a mix of cout and cerr
Include log_internal.h to use the LOG() helper macro
- Avoid including log_internal.h in any code that may pollute C++ driver headers.
- Use MONGO_LOG() instead of LOG() for code included by C++ driver headers.

Normal Logging¶

Debugging with levels of verbosity. See the -v command line option (default level is 0). If the global log level is less than x, no functions in the steam are executed.
```
LOG( int x ) << ...
```
Informational
```
log() << ...
```
Rate limited
```
LOGSOME() << ...
```
Warnings
- recoverable, e.g. replica set node down
```
warning() << ...
```
Errors
- unexpected system state (disk full)
- internal code errors
```
error() << ...
```

Debugging Helpers¶

PRINT( x ) - prints expression text and value (can also do PRINT(x.method()))
PRINTFL - prints file and line (good for tracing execution)
printStackTrace() - shows a stack trace. Alternative to using a debugger.
GEODEBUG, etc... - used for incredibly verbose logging for a section of code that has to be turned on at compile time