1 // Copyright 2020 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
6 Package metrics provides a stable interface to access implementation-defined
7 metrics exported by the Go runtime. This package is similar to existing functions
8 like runtime.ReadMemStats and debug.ReadGCStats, but significantly more general.
10 The set of metrics defined by this package may evolve as the runtime itself
11 evolves, and also enables variation across Go implementations, whose relevant
12 metric sets may not intersect.
16 Metrics are designated by a string key, rather than, for example, a field name in
17 a struct. The full list of supported metrics is always available in the slice of
18 Descriptions returned by All. Each Description also includes useful information
19 about the metric, such as how to display it (e.g. gauge vs. counter) and how difficult
20 or disruptive it is to obtain it (e.g. do you need to stop the world?).
22 Thus, users of this API are encouraged to sample supported metrics defined by the
23 slice returned by All to remain compatible across Go versions. Of course, situations
24 arise where reading specific metrics is critical. For these cases, users are
25 encouranged to use build tags, and although metrics may be deprecated and removed,
26 users should consider this to be an exceptional and rare event, coinciding with a
27 very large change in a particular Go implementation.
29 Each metric key also has a "kind" that describes the format of the metric's value.
30 In the interest of not breaking users of this package, the "kind" for a given metric
31 is guaranteed not to change. If it must change, then a new metric will be introduced
32 with a new key and a new "kind."
36 As mentioned earlier, metric keys are strings. Their format is simple and well-defined,
37 designed to be both human and machine readable. It is split into two components,
38 separated by a colon: a rooted path and a unit. The choice to include the unit in
39 the key is motivated by compatibility: if a metric's unit changes, its semantics likely
40 did also, and a new key should be introduced.
42 For more details on the precise definition of the metric key's path and unit formats, see
43 the documentation of the Name field of the Description struct.
47 This package supports metrics whose values have a floating-point representation. In
48 order to improve ease-of-use, this package promises to never produce the following
49 classes of floating-point values: NaN, infinity.
53 Below is the full list of supported metrics, ordered lexicographically.
55 /gc/cycles/automatic:gc-cycles
56 Count of completed GC cycles generated by the Go runtime.
58 /gc/cycles/forced:gc-cycles
59 Count of completed GC cycles forced by the application.
61 /gc/cycles/total:gc-cycles
62 Count of all completed GC cycles.
64 /gc/heap/allocs-by-size:bytes
65 Distribution of all objects allocated by approximate size.
67 /gc/heap/frees-by-size:bytes
68 Distribution of all objects freed by approximate size.
71 Heap size target for the end of the GC cycle.
73 /gc/heap/objects:objects
74 Number of objects, live or unswept, occupying heap memory.
77 Distribution individual GC-related stop-the-world pause latencies.
79 /memory/classes/heap/free:bytes
80 Memory that is completely free and eligible to be returned to
81 the underlying system, but has not been. This metric is the
82 runtime's estimate of free address space that is backed by
85 /memory/classes/heap/objects:bytes
86 Memory occupied by live objects and dead objects that have
87 not yet been marked free by the garbage collector.
89 /memory/classes/heap/released:bytes
90 Memory that is completely free and has been returned to
91 the underlying system. This metric is the runtime's estimate of
92 free address space that is still mapped into the process, but
93 is not backed by physical memory.
95 /memory/classes/heap/stacks:bytes
96 Memory allocated from the heap that is reserved for stack
97 space, whether or not it is currently in-use.
99 /memory/classes/heap/unused:bytes
100 Memory that is reserved for heap objects but is not currently
101 used to hold heap objects.
103 /memory/classes/metadata/mcache/free:bytes
104 Memory that is reserved for runtime mcache structures, but
107 /memory/classes/metadata/mcache/inuse:bytes
108 Memory that is occupied by runtime mcache structures that
109 are currently being used.
111 /memory/classes/metadata/mspan/free:bytes
112 Memory that is reserved for runtime mspan structures, but
115 /memory/classes/metadata/mspan/inuse:bytes
116 Memory that is occupied by runtime mspan structures that are
117 currently being used.
119 /memory/classes/metadata/other:bytes
120 Memory that is reserved for or used to hold runtime
123 /memory/classes/os-stacks:bytes
124 Stack memory allocated by the underlying operating system.
126 /memory/classes/other:bytes
127 Memory used by execution trace buffers, structures for
128 debugging the runtime, finalizer and profiler specials, and
131 /memory/classes/profiling/buckets:bytes
132 Memory that is used by the stack trace hash map used for
135 /memory/classes/total:bytes
136 All memory mapped by the Go runtime into the current process
137 as read-write. Note that this does not include memory mapped
138 by code called via cgo or via the syscall package.
139 Sum of all metrics in /memory/classes.
141 /sched/goroutines:goroutines
142 Count of live goroutines.