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.
5 // Note: run 'go generate' (which will run 'go test -generate') to update the "Supported metrics" list.
6 //go:generate go test -run=Docs -generate
9 Package metrics provides a stable interface to access implementation-defined
10 metrics exported by the Go runtime. This package is similar to existing functions
11 like [runtime.ReadMemStats] and [debug.ReadGCStats], but significantly more general.
13 The set of metrics defined by this package may evolve as the runtime itself
14 evolves, and also enables variation across Go implementations, whose relevant
15 metric sets may not intersect.
19 Metrics are designated by a string key, rather than, for example, a field name in
20 a struct. The full list of supported metrics is always available in the slice of
21 Descriptions returned by All. Each Description also includes useful information
24 Thus, users of this API are encouraged to sample supported metrics defined by the
25 slice returned by All to remain compatible across Go versions. Of course, situations
26 arise where reading specific metrics is critical. For these cases, users are
27 encouraged to use build tags, and although metrics may be deprecated and removed,
28 users should consider this to be an exceptional and rare event, coinciding with a
29 very large change in a particular Go implementation.
31 Each metric key also has a "kind" that describes the format of the metric's value.
32 In the interest of not breaking users of this package, the "kind" for a given metric
33 is guaranteed not to change. If it must change, then a new metric will be introduced
34 with a new key and a new "kind."
38 As mentioned earlier, metric keys are strings. Their format is simple and well-defined,
39 designed to be both human and machine readable. It is split into two components,
40 separated by a colon: a rooted path and a unit. The choice to include the unit in
41 the key is motivated by compatibility: if a metric's unit changes, its semantics likely
42 did also, and a new key should be introduced.
44 For more details on the precise definition of the metric key's path and unit formats, see
45 the documentation of the Name field of the Description struct.
49 This package supports metrics whose values have a floating-point representation. In
50 order to improve ease-of-use, this package promises to never produce the following
51 classes of floating-point values: NaN, infinity.
55 Below is the full list of supported metrics, ordered lexicographically.
57 /cgo/go-to-c-calls:calls
58 Count of calls made from Go to C by the current process.
60 /cpu/classes/gc/mark/assist:cpu-seconds
61 Estimated total CPU time goroutines spent performing GC
62 tasks to assist the GC and prevent it from falling behind the
63 application. This metric is an overestimate, and not directly
64 comparable to system CPU time measurements. Compare only with
65 other /cpu/classes metrics.
67 /cpu/classes/gc/mark/dedicated:cpu-seconds
68 Estimated total CPU time spent performing GC tasks on processors
69 (as defined by GOMAXPROCS) dedicated to those tasks. This
70 includes time spent with the world stopped due to the GC. This
71 metric is an overestimate, and not directly comparable to system
72 CPU time measurements. Compare only with other /cpu/classes
75 /cpu/classes/gc/mark/idle:cpu-seconds
76 Estimated total CPU time spent performing GC tasks on spare CPU
77 resources that the Go scheduler could not otherwise find a use
78 for. This should be subtracted from the total GC CPU time to
79 obtain a measure of compulsory GC CPU time. This metric is an
80 overestimate, and not directly comparable to system CPU time
81 measurements. Compare only with other /cpu/classes metrics.
83 /cpu/classes/gc/pause:cpu-seconds
84 Estimated total CPU time spent with the application paused by
85 the GC. Even if only one thread is running during the pause,
86 this is computed as GOMAXPROCS times the pause latency because
87 nothing else can be executing. This is the exact sum of samples
88 in /gc/pause:seconds if each sample is multiplied by GOMAXPROCS
89 at the time it is taken. This metric is an overestimate,
90 and not directly comparable to system CPU time measurements.
91 Compare only with other /cpu/classes metrics.
93 /cpu/classes/gc/total:cpu-seconds
94 Estimated total CPU time spent performing GC tasks. This metric
95 is an overestimate, and not directly comparable to system CPU
96 time measurements. Compare only with other /cpu/classes metrics.
97 Sum of all metrics in /cpu/classes/gc.
99 /cpu/classes/idle:cpu-seconds
100 Estimated total available CPU time not spent executing
101 any Go or Go runtime code. In other words, the part of
102 /cpu/classes/total:cpu-seconds that was unused. This metric is
103 an overestimate, and not directly comparable to system CPU time
104 measurements. Compare only with other /cpu/classes metrics.
106 /cpu/classes/scavenge/assist:cpu-seconds
107 Estimated total CPU time spent returning unused memory to the
108 underlying platform in response eagerly in response to memory
109 pressure. This metric is an overestimate, and not directly
110 comparable to system CPU time measurements. Compare only with
111 other /cpu/classes metrics.
113 /cpu/classes/scavenge/background:cpu-seconds
114 Estimated total CPU time spent performing background tasks to
115 return unused memory to the underlying platform. This metric is
116 an overestimate, and not directly comparable to system CPU time
117 measurements. Compare only with other /cpu/classes metrics.
119 /cpu/classes/scavenge/total:cpu-seconds
120 Estimated total CPU time spent performing tasks that return
121 unused memory to the underlying platform. This metric is an
122 overestimate, and not directly comparable to system CPU time
123 measurements. Compare only with other /cpu/classes metrics.
124 Sum of all metrics in /cpu/classes/scavenge.
126 /cpu/classes/total:cpu-seconds
127 Estimated total available CPU time for user Go code or the Go
128 runtime, as defined by GOMAXPROCS. In other words, GOMAXPROCS
129 integrated over the wall-clock duration this process has been
130 executing for. This metric is an overestimate, and not directly
131 comparable to system CPU time measurements. Compare only with
132 other /cpu/classes metrics. Sum of all metrics in /cpu/classes.
134 /cpu/classes/user:cpu-seconds
135 Estimated total CPU time spent running user Go code. This may
136 also include some small amount of time spent in the Go runtime.
137 This metric is an overestimate, and not directly comparable
138 to system CPU time measurements. Compare only with other
139 /cpu/classes metrics.
141 /gc/cycles/automatic:gc-cycles
142 Count of completed GC cycles generated by the Go runtime.
144 /gc/cycles/forced:gc-cycles
145 Count of completed GC cycles forced by the application.
147 /gc/cycles/total:gc-cycles
148 Count of all completed GC cycles.
151 Heap size target percentage configured by the user, otherwise
152 100. This value is set by the GOGC environment variable, and the
153 runtime/debug.SetGCPercent function.
156 Go runtime memory limit configured by the user, otherwise
157 math.MaxInt64. This value is set by the GOMEMLIMIT environment
158 variable, and the runtime/debug.SetMemoryLimit function.
160 /gc/heap/allocs-by-size:bytes
161 Distribution of heap allocations by approximate size.
162 Bucket counts increase monotonically. Note that this does not
163 include tiny objects as defined by /gc/heap/tiny/allocs:objects,
166 /gc/heap/allocs:bytes
167 Cumulative sum of memory allocated to the heap by the
170 /gc/heap/allocs:objects
171 Cumulative count of heap allocations triggered by the
172 application. Note that this does not include tiny objects as
173 defined by /gc/heap/tiny/allocs:objects, only tiny blocks.
175 /gc/heap/frees-by-size:bytes
176 Distribution of freed heap allocations by approximate size.
177 Bucket counts increase monotonically. Note that this does not
178 include tiny objects as defined by /gc/heap/tiny/allocs:objects,
182 Cumulative sum of heap memory freed by the garbage collector.
184 /gc/heap/frees:objects
185 Cumulative count of heap allocations whose storage was freed
186 by the garbage collector. Note that this does not include tiny
187 objects as defined by /gc/heap/tiny/allocs:objects, only tiny
191 Heap size target for the end of the GC cycle.
194 Heap memory occupied by live objects that were marked by the
197 /gc/heap/objects:objects
198 Number of objects, live or unswept, occupying heap memory.
200 /gc/heap/tiny/allocs:objects
201 Count of small allocations that are packed together into blocks.
202 These allocations are counted separately from other allocations
203 because each individual allocation is not tracked by the
204 runtime, only their block. Each block is already accounted for
205 in allocs-by-size and frees-by-size.
207 /gc/limiter/last-enabled:gc-cycle
208 GC cycle the last time the GC CPU limiter was enabled.
209 This metric is useful for diagnosing the root cause of an
210 out-of-memory error, because the limiter trades memory for CPU
211 time when the GC's CPU time gets too high. This is most likely
212 to occur with use of SetMemoryLimit. The first GC cycle is cycle
213 1, so a value of 0 indicates that it was never enabled.
216 Distribution of individual GC-related stop-the-world pause
217 latencies. Bucket counts increase monotonically.
219 /gc/scan/globals:bytes
220 The total amount of global variable space that is scannable.
223 The total amount of heap space that is scannable.
226 The number of bytes of stack that were scanned last GC cycle.
229 The total amount space that is scannable. Sum of all metrics in
232 /gc/stack/starting-size:bytes
233 The stack size of new goroutines.
235 /godebug/non-default-behavior/execerrdot:events
236 The number of non-default behaviors executed by the os/exec
237 package due to a non-default GODEBUG=execerrdot=... setting.
239 /godebug/non-default-behavior/http2client:events
240 The number of non-default behaviors executed by the net/http
241 package due to a non-default GODEBUG=http2client=... setting.
243 /godebug/non-default-behavior/http2server:events
244 The number of non-default behaviors executed by the net/http
245 package due to a non-default GODEBUG=http2server=... setting.
247 /godebug/non-default-behavior/installgoroot:events
248 The number of non-default behaviors executed by the go/build
249 package due to a non-default GODEBUG=installgoroot=... setting.
251 /godebug/non-default-behavior/jstmpllitinterp:events
252 The number of non-default behaviors executed by
253 the html/template package due to a non-default
254 GODEBUG=jstmpllitinterp=... setting.
256 /godebug/non-default-behavior/multipartmaxheaders:events
257 The number of non-default behaviors executed by
258 the mime/multipart package due to a non-default
259 GODEBUG=multipartmaxheaders=... setting.
261 /godebug/non-default-behavior/multipartmaxparts:events
262 The number of non-default behaviors executed by
263 the mime/multipart package due to a non-default
264 GODEBUG=multipartmaxparts=... setting.
266 /godebug/non-default-behavior/panicnil:events
267 The number of non-default behaviors executed by the runtime
268 package due to a non-default GODEBUG=panicnil=... setting.
270 /godebug/non-default-behavior/randautoseed:events
271 The number of non-default behaviors executed by the math/rand
272 package due to a non-default GODEBUG=randautoseed=... setting.
274 /godebug/non-default-behavior/tarinsecurepath:events
275 The number of non-default behaviors executed by the archive/tar
276 package due to a non-default GODEBUG=tarinsecurepath=...
279 /godebug/non-default-behavior/x509sha1:events
280 The number of non-default behaviors executed by the crypto/x509
281 package due to a non-default GODEBUG=x509sha1=... setting.
283 /godebug/non-default-behavior/x509usefallbackroots:events
284 The number of non-default behaviors executed by the crypto/x509
285 package due to a non-default GODEBUG=x509usefallbackroots=...
288 /godebug/non-default-behavior/zipinsecurepath:events
289 The number of non-default behaviors executed by the archive/zip
290 package due to a non-default GODEBUG=zipinsecurepath=...
293 /memory/classes/heap/free:bytes
294 Memory that is completely free and eligible to be returned to
295 the underlying system, but has not been. This metric is the
296 runtime's estimate of free address space that is backed by
299 /memory/classes/heap/objects:bytes
300 Memory occupied by live objects and dead objects that have not
301 yet been marked free by the garbage collector.
303 /memory/classes/heap/released:bytes
304 Memory that is completely free and has been returned to the
305 underlying system. This metric is the runtime's estimate of free
306 address space that is still mapped into the process, but is not
307 backed by physical memory.
309 /memory/classes/heap/stacks:bytes
310 Memory allocated from the heap that is reserved for stack space,
311 whether or not it is currently in-use.
313 /memory/classes/heap/unused:bytes
314 Memory that is reserved for heap objects but is not currently
315 used to hold heap objects.
317 /memory/classes/metadata/mcache/free:bytes
318 Memory that is reserved for runtime mcache structures, but not
321 /memory/classes/metadata/mcache/inuse:bytes
322 Memory that is occupied by runtime mcache structures that are
323 currently being used.
325 /memory/classes/metadata/mspan/free:bytes
326 Memory that is reserved for runtime mspan structures, but not
329 /memory/classes/metadata/mspan/inuse:bytes
330 Memory that is occupied by runtime mspan structures that are
331 currently being used.
333 /memory/classes/metadata/other:bytes
334 Memory that is reserved for or used to hold runtime metadata.
336 /memory/classes/os-stacks:bytes
337 Stack memory allocated by the underlying operating system.
339 /memory/classes/other:bytes
340 Memory used by execution trace buffers, structures for debugging
341 the runtime, finalizer and profiler specials, and more.
343 /memory/classes/profiling/buckets:bytes
344 Memory that is used by the stack trace hash map used for
347 /memory/classes/total:bytes
348 All memory mapped by the Go runtime into the current process
349 as read-write. Note that this does not include memory mapped
350 by code called via cgo or via the syscall package. Sum of all
351 metrics in /memory/classes.
353 /sched/gomaxprocs:threads
354 The current runtime.GOMAXPROCS setting, or the number of
355 operating system threads that can execute user-level Go code
358 /sched/goroutines:goroutines
359 Count of live goroutines.
361 /sched/latencies:seconds
362 Distribution of the time goroutines have spent in the scheduler
363 in a runnable state before actually running. Bucket counts
364 increase monotonically.
366 /sync/mutex/wait/total:seconds
367 Approximate cumulative time goroutines have spent blocked
368 on a sync.Mutex or sync.RWMutex. This metric is useful for
369 identifying global changes in lock contention. Collect a mutex
370 or block profile using the runtime/pprof package for more
371 detailed contention data.