mirror of
https://github.com/ceph/ceph
synced 2024-12-09 13:08:28 +00:00
983071b925
Signed-off-by: Shinobu Kinjo <shinobu@redhat.com>
56 lines
2.5 KiB
ReStructuredText
56 lines
2.5 KiB
ReStructuredText
============
|
|
Debug logs
|
|
============
|
|
|
|
The main debugging tool for Ceph is the dout and derr logging functions.
|
|
Collectively, these are referred to as "dout logging."
|
|
|
|
Dout has several log faculties, which can be set at various log
|
|
levels using the configuration management system. So it is possible to enable
|
|
debugging just for the messenger, by setting debug_ms to 10, for example.
|
|
|
|
The dout macro avoids even generating log messages which are not going to be
|
|
used, by enclosing them in an "if" statement. What this means is that if you
|
|
have the debug level set at 0, and you run this code::
|
|
|
|
dout(20) << "myfoo() = " << myfoo() << dendl;
|
|
|
|
|
|
myfoo() will not be called here.
|
|
|
|
Unfortunately, the performance of debug logging is relatively low. This is
|
|
because there is a single, process-wide mutex which every debug output
|
|
statement takes, and every debug output statement leads to a write() system
|
|
call or a call to syslog(). There is also a computational overhead to using C++
|
|
streams to consider. So you will need to be parsimonious in your logging to get
|
|
the best performance.
|
|
|
|
Sometimes, enabling logging can hide race conditions and other bugs by changing
|
|
the timing of events. Keep this in mind when debugging.
|
|
|
|
Performance counters
|
|
====================
|
|
|
|
Ceph daemons use performance counters to track key statistics like number of
|
|
inodes pinned. Performance counters are essentially sets of integers and floats
|
|
which can be set, incremented, and read using the PerfCounters API.
|
|
|
|
A PerfCounters object is usually associated with a single subsystem. It
|
|
contains multiple counters. This object is thread-safe because it is protected
|
|
by an internal mutex. You can create multiple PerfCounters objects.
|
|
|
|
Currently, three types of performance counters are supported: u64 counters,
|
|
float counters, and long-run floating-point average counters. These are created
|
|
by PerfCountersBuilder::add_u64, PerfCountersBuilder::add_fl, and
|
|
PerfCountersBuilder::add_fl_avg, respectively. u64 and float counters simply
|
|
provide a single value which can be updated, incremented, and read atomically.
|
|
floating-pointer average counters provide two values: the current total, and
|
|
the number of times the total has been changed. This is intended to provide a
|
|
long-run average value.
|
|
|
|
Performance counter information can be read in JSON format from the
|
|
administrative socket (admin_sock). This is implemented as a UNIX domain
|
|
socket. The Ceph performance counter plugin for collectd shows an example of how
|
|
to access this information. Another example can be found in the unit tests for
|
|
the administrative sockets.
|