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 /gc/cycles/automatic:gc-cycles
48 Count of completed GC cycles generated by the Go runtime.
50 /gc/cycles/forced:gc-cycles
51 Count of completed forced GC cycles.
53 /gc/cycles/total:gc-cycles
54 Count of all completed GC cycles.
57 Heap size target for the end of the GC cycle.
59 /gc/heap/objects:objects
60 Number of objects, live or unswept, occupying heap memory.
62 /memory/classes/heap/free:bytes
63 Memory that is available for allocation, and may be returned
64 to the underlying system.
66 /memory/classes/heap/objects:bytes
67 Memory occupied by live objects and dead objects that have
68 not yet been collected.
70 /memory/classes/heap/released:bytes
71 Memory that has been returned to the underlying system.
73 /memory/classes/heap/stacks:bytes
74 Memory allocated from the heap that is occupied by stacks.
76 /memory/classes/heap/unused:bytes
77 Memory that is unavailable for allocation, but cannot be
78 returned to the underlying system.
80 /memory/classes/metadata/mcache/free:bytes
81 Memory that is reserved for runtime mcache structures, but
84 /memory/classes/metadata/mcache/inuse:bytes
85 Memory that is occupied by runtime mcache structures that
86 are currently being used.
88 /memory/classes/metadata/mspan/free:bytes
89 Memory that is reserved for runtime mspan structures, but
92 /memory/classes/metadata/mspan/inuse:bytes
93 Memory that is occupied by runtime mspan structures that are
96 /memory/classes/metadata/other:bytes
97 Memory that is reserved for or used to hold runtime
100 /memory/classes/os-stacks:bytes
101 Stack memory allocated by the underlying operating system.
103 /memory/classes/other:bytes
104 Memory used by execution trace buffers, structures for
105 debugging the runtime, finalizer and profiler specials, and
108 /memory/classes/profiling/buckets:bytes
109 Memory that is used by the stack trace hash map used for
112 /memory/classes/total:bytes
113 All memory mapped by the Go runtime into the current process
114 as read-write. Note that this does not include memory mapped
115 by code called via cgo or via the syscall package.
116 Sum of all metrics in /memory/classes.