Because the string concatenation requires allocation of a new string, which will need to be garbage collected, regardless of whether or not the log.debug actually needs it.
Using a format and args lets you call the method with only references to existing objects, no additional string needs to be allocated unless the log method actually needs to generate the string to log (and it might even be able to use streaming to output the log and never even allocate the string)
When you’re doing things like putting trace logs with all your parameters in at the top of every method call, the memory and GC pressure of generating unnecessary strings can be significant.
Generally, most logging frameworks have two parts, the format string, and the parameters. A good logging library will also avoid calling str()/toString() if the log isn't emitted (for example, if it's a debug log but minimum level is info).
You have something similar when building database queries, generally you should have a base template into which you insert arguments. The library generally should take care of escaping things and also preventing things like SQL injections.
jameshart|4 years ago
Using a format and args lets you call the method with only references to existing objects, no additional string needs to be allocated unless the log method actually needs to generate the string to log (and it might even be able to use streaming to output the log and never even allocate the string)
When you’re doing things like putting trace logs with all your parameters in at the top of every method call, the memory and GC pressure of generating unnecessary strings can be significant.
mshanu|4 years ago
ehsankia|4 years ago
You have something similar when building database queries, generally you should have a base template into which you insert arguments. The library generally should take care of escaping things and also preventing things like SQL injections.