mirror of https://github.com/ceph/ceph
32 lines
1.2 KiB
ReStructuredText
32 lines
1.2 KiB
ReStructuredText
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============
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Debug Logs
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============
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The main debugging tool for Ceph is the dout and derr logging functions.
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Collectively, these are referred to as "dout logging."
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Dout has several log faculties, which can be set at various log
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levels using the configuration management system. So it is possible to enable
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debugging just for the messenger, by setting debug_ms to 10, for example.
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Dout is implemented mainly in common/DoutStreambuf.cc
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The dout macro avoids even generating log messages which are not going to be
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used, by enclosing them in an "if" statement. What this means is that if you
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have the debug level set at 0, and you run this code
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``dout(20) << "myfoo() = " << myfoo() << dendl;``
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myfoo() will not be called here.
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Unfortunately, the performance of debug logging is relatively low. This is
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because there is a single, process-wide mutex which every debug output
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statement takes, and every debug output statement leads to a write() system
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call or a call to syslog(). There is also a computational overhead to using C++
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streams to consider. So you will need to be parsimonius in your logging to get
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the best performance.
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Sometimes, enabling logging can hide race conditions and other bugs by changing
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the timing of events. Keep this in mind when debugging.
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