Debug output for cache misses only

[rollysys]

Actually we have use ccache as a must have component in our jenkins job.
Then I need to monitor all jenkins job's "ccache missing stat data" for enhancing the ccache policy.
So can we only get debug output files for missed object? Because the project is very large.
Thanks!

[afbjorklund]

Added a setting to be able to control which cache debug files are left on exit:

(default) debug = false
(default) debug_dir = 
(default) debug_hits = true
(default) debug_level = 2

[afbjorklund]

One drawback with this method (running debug=true in production, for misses) is that you don't get anything to compare with. So you need to keep debug_dir from a build with debug_hits=true, in order to have anything to compare with...

One method of debugging would be to run one build with debug=true debug_dir=d1 debug_hits=true, then do a make clean, run another build with debug=true debug_dir=d2 debug_hits=false, and look for any files in the second dir.

[jrosdahl]

I'm not fully convinced that just saving debug files for misses is a reasonable use case since (as @afbjorklund says) you often need debug information from hits to compare the misses to.

But if we do want to support it, I'm not sure that adding yet another boolean configuration option would be the way to go – there might be other debug output tweaks that are wanted in the future, necessitating even more configuration options. In retrospect, I think that it was a mistake to accept #1312 in that form.

I'd rather suggest to redesign the configuration options, maybe like this (just a quick sketch):

• debug = false: Disable debugging (the default).
• debug = true: Enable full debugging.
• debug = output:log,input-text: Enable debugging, but only write the .ccache-log and .ccache-input-text files.
• debug = result:cache_miss,unsupported_*: Enable debugging, but only when one of the results is cache_miss or matches unsupported_*.

These can be combined, e.g. debug = output:log result:cache_miss. debug_level can be removed.