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
21 Thus, users of this API are encouraged to sample supported metrics defined by the
22 slice returned by All to remain compatible across Go versions. Of course, situations
23 arise where reading specific metrics is critical. For these cases, users are
24 encouraged to use build tags, and although metrics may be deprecated and removed,
25 users should consider this to be an exceptional and rare event, coinciding with a
26 very large change in a particular Go implementation.
28 Each metric key also has a "kind" that describes the format of the metric's value.
29 In the interest of not breaking users of this package, the "kind" for a given metric
30 is guaranteed not to change. If it must change, then a new metric will be introduced
31 with a new key and a new "kind."
35 As mentioned earlier, metric keys are strings. Their format is simple and well-defined,
36 designed to be both human and machine readable. It is split into two components,
37 separated by a colon: a rooted path and a unit. The choice to include the unit in
38 the key is motivated by compatibility: if a metric's unit changes, its semantics likely
39 did also, and a new key should be introduced.
41 For more details on the precise definition of the metric key's path and unit formats, see
42 the documentation of the Name field of the Description struct.
46 This package supports metrics whose values have a floating-point representation. In
47 order to improve ease-of-use, this package promises to never produce the following
48 classes of floating-point values: NaN, infinity.
52 Below is the full list of supported metrics, ordered lexicographically.
54 /gc/cycles/automatic:gc-cycles
55 Count of completed GC cycles generated by the Go runtime.
57 /gc/cycles/forced:gc-cycles
58 Count of completed GC cycles forced by the application.
60 /gc/cycles/total:gc-cycles
61 Count of all completed GC cycles.
63 /gc/heap/allocs-by-size:bytes
64 Distribution of all objects allocated by approximate size.
66 /gc/heap/frees-by-size:bytes
67 Distribution of all objects freed by approximate size.
70 Heap size target for the end of the GC cycle.
72 /gc/heap/objects:objects
73 Number of objects, live or unswept, occupying heap memory.
76 Distribution individual GC-related stop-the-world pause latencies.
78 /memory/classes/heap/free:bytes
79 Memory that is completely free and eligible to be returned to
80 the underlying system, but has not been. This metric is the
81 runtime's estimate of free address space that is backed by
84 /memory/classes/heap/objects:bytes
85 Memory occupied by live objects and dead objects that have
86 not yet been marked free by the garbage collector.
88 /memory/classes/heap/released:bytes
89 Memory that is completely free and has been returned to
90 the underlying system. This metric is the runtime's estimate of
91 free address space that is still mapped into the process, but
92 is not backed by physical memory.
94 /memory/classes/heap/stacks:bytes
95 Memory allocated from the heap that is reserved for stack
96 space, whether or not it is currently in-use.
98 /memory/classes/heap/unused:bytes
99 Memory that is reserved for heap objects but is not currently
100 used to hold heap objects.
102 /memory/classes/metadata/mcache/free:bytes
103 Memory that is reserved for runtime mcache structures, but
106 /memory/classes/metadata/mcache/inuse:bytes
107 Memory that is occupied by runtime mcache structures that
108 are currently being used.
110 /memory/classes/metadata/mspan/free:bytes
111 Memory that is reserved for runtime mspan structures, but
114 /memory/classes/metadata/mspan/inuse:bytes
115 Memory that is occupied by runtime mspan structures that are
116 currently being used.
118 /memory/classes/metadata/other:bytes
119 Memory that is reserved for or used to hold runtime
122 /memory/classes/os-stacks:bytes
123 Stack memory allocated by the underlying operating system.
125 /memory/classes/other:bytes
126 Memory used by execution trace buffers, structures for
127 debugging the runtime, finalizer and profiler specials, and
130 /memory/classes/profiling/buckets:bytes
131 Memory that is used by the stack trace hash map used for
134 /memory/classes/total:bytes
135 All memory mapped by the Go runtime into the current process
136 as read-write. Note that this does not include memory mapped
137 by code called via cgo or via the syscall package.
138 Sum of all metrics in /memory/classes.
140 /sched/goroutines:goroutines
141 Count of live goroutines.