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 heap allocations by approximate size.
65 Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects,
69 Cumulative sum of memory allocated to the heap by the application.
71 /gc/heap/allocs:objects
72 Cumulative count of heap allocations triggered by the application.
73 Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects,
76 /gc/heap/frees-by-size:bytes
77 Distribution of freed heap allocations by approximate size.
78 Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects,
82 Cumulative sum of heap memory freed by the garbage collector.
84 /gc/heap/frees:objects
85 Cumulative count of heap allocations whose storage was freed by the garbage collector.
86 Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects,
90 Heap size target for the end of the GC cycle.
92 /gc/heap/objects:objects
93 Number of objects, live or unswept, occupying heap memory.
95 /gc/heap/tiny/allocs:objects
96 Count of small allocations that are packed together into blocks.
97 These allocations are counted separately from other allocations
98 because each individual allocation is not tracked by the runtime,
99 only their block. Each block is already accounted for in
100 allocs-by-size and frees-by-size.
103 Distribution individual GC-related stop-the-world pause latencies.
105 /gc/stack/starting-size:bytes
106 The stack size of new goroutines.
108 /memory/classes/heap/free:bytes
109 Memory that is completely free and eligible to be returned to
110 the underlying system, but has not been. This metric is the
111 runtime's estimate of free address space that is backed by
114 /memory/classes/heap/objects:bytes
115 Memory occupied by live objects and dead objects that have
116 not yet been marked free by the garbage collector.
118 /memory/classes/heap/released:bytes
119 Memory that is completely free and has been returned to
120 the underlying system. This metric is the runtime's estimate of
121 free address space that is still mapped into the process, but
122 is not backed by physical memory.
124 /memory/classes/heap/stacks:bytes
125 Memory allocated from the heap that is reserved for stack
126 space, whether or not it is currently in-use.
128 /memory/classes/heap/unused:bytes
129 Memory that is reserved for heap objects but is not currently
130 used to hold heap objects.
132 /memory/classes/metadata/mcache/free:bytes
133 Memory that is reserved for runtime mcache structures, but
136 /memory/classes/metadata/mcache/inuse:bytes
137 Memory that is occupied by runtime mcache structures that
138 are currently being used.
140 /memory/classes/metadata/mspan/free:bytes
141 Memory that is reserved for runtime mspan structures, but
144 /memory/classes/metadata/mspan/inuse:bytes
145 Memory that is occupied by runtime mspan structures that are
146 currently being used.
148 /memory/classes/metadata/other:bytes
149 Memory that is reserved for or used to hold runtime
152 /memory/classes/os-stacks:bytes
153 Stack memory allocated by the underlying operating system.
155 /memory/classes/other:bytes
156 Memory used by execution trace buffers, structures for
157 debugging the runtime, finalizer and profiler specials, and
160 /memory/classes/profiling/buckets:bytes
161 Memory that is used by the stack trace hash map used for
164 /memory/classes/total:bytes
165 All memory mapped by the Go runtime into the current process
166 as read-write. Note that this does not include memory mapped
167 by code called via cgo or via the syscall package.
168 Sum of all metrics in /memory/classes.
170 /sched/goroutines:goroutines
171 Count of live goroutines.
173 /sched/latencies:seconds
174 Distribution of the time goroutines have spent in the scheduler
175 in a runnable state before actually running.