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. 4 5 /* 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. 9 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. 13 14 # Interface 15 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. 20 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. 27 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." 32 33 # Metric key format 34 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. 40 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. 43 44 # A note about floats 45 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. 49 50 # Supported metrics 51 52 Below is the full list of supported metrics, ordered lexicographically. 53 54 /cgo/go-to-c-calls:calls 55 Count of calls made from Go to C by the current process. 56 57 /gc/cycles/automatic:gc-cycles 58 Count of completed GC cycles generated by the Go runtime. 59 60 /gc/cycles/forced:gc-cycles 61 Count of completed GC cycles forced by the application. 62 63 /gc/cycles/total:gc-cycles 64 Count of all completed GC cycles. 65 66 /gc/heap/allocs-by-size:bytes 67 Distribution of heap allocations by approximate size. 68 Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects, 69 only tiny blocks. 70 71 /gc/heap/allocs:bytes 72 Cumulative sum of memory allocated to the heap by the application. 73 74 /gc/heap/allocs:objects 75 Cumulative count of heap allocations triggered by the application. 76 Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects, 77 only tiny blocks. 78 79 /gc/heap/frees-by-size:bytes 80 Distribution of freed heap allocations by approximate size. 81 Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects, 82 only tiny blocks. 83 84 /gc/heap/frees:bytes 85 Cumulative sum of heap memory freed by the garbage collector. 86 87 /gc/heap/frees:objects 88 Cumulative count of heap allocations whose storage was freed by the garbage collector. 89 Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects, 90 only tiny blocks. 91 92 /gc/heap/goal:bytes 93 Heap size target for the end of the GC cycle. 94 95 /gc/heap/objects:objects 96 Number of objects, live or unswept, occupying heap memory. 97 98 /gc/heap/tiny/allocs:objects 99 Count of small allocations that are packed together into blocks. 100 These allocations are counted separately from other allocations 101 because each individual allocation is not tracked by the runtime, 102 only their block. Each block is already accounted for in 103 allocs-by-size and frees-by-size. 104 105 /gc/limiter/last-enabled:gc-cycle 106 GC cycle the last time the GC CPU limiter was enabled. 107 This metric is useful for diagnosing the root cause of an out-of-memory 108 error, because the limiter trades memory for CPU time when the GC's CPU 109 time gets too high. This is most likely to occur with use of SetMemoryLimit. 110 The first GC cycle is cycle 1, so a value of 0 indicates that it was never enabled. 111 112 /gc/pauses:seconds 113 Distribution individual GC-related stop-the-world pause latencies. 114 115 /gc/stack/starting-size:bytes 116 The stack size of new goroutines. 117 118 /memory/classes/heap/free:bytes 119 Memory that is completely free and eligible to be returned to 120 the underlying system, but has not been. This metric is the 121 runtime's estimate of free address space that is backed by 122 physical memory. 123 124 /memory/classes/heap/objects:bytes 125 Memory occupied by live objects and dead objects that have 126 not yet been marked free by the garbage collector. 127 128 /memory/classes/heap/released:bytes 129 Memory that is completely free and has been returned to 130 the underlying system. This metric is the runtime's estimate of 131 free address space that is still mapped into the process, but 132 is not backed by physical memory. 133 134 /memory/classes/heap/stacks:bytes 135 Memory allocated from the heap that is reserved for stack 136 space, whether or not it is currently in-use. 137 138 /memory/classes/heap/unused:bytes 139 Memory that is reserved for heap objects but is not currently 140 used to hold heap objects. 141 142 /memory/classes/metadata/mcache/free:bytes 143 Memory that is reserved for runtime mcache structures, but 144 not in-use. 145 146 /memory/classes/metadata/mcache/inuse:bytes 147 Memory that is occupied by runtime mcache structures that 148 are currently being used. 149 150 /memory/classes/metadata/mspan/free:bytes 151 Memory that is reserved for runtime mspan structures, but 152 not in-use. 153 154 /memory/classes/metadata/mspan/inuse:bytes 155 Memory that is occupied by runtime mspan structures that are 156 currently being used. 157 158 /memory/classes/metadata/other:bytes 159 Memory that is reserved for or used to hold runtime 160 metadata. 161 162 /memory/classes/os-stacks:bytes 163 Stack memory allocated by the underlying operating system. 164 165 /memory/classes/other:bytes 166 Memory used by execution trace buffers, structures for 167 debugging the runtime, finalizer and profiler specials, and 168 more. 169 170 /memory/classes/profiling/buckets:bytes 171 Memory that is used by the stack trace hash map used for 172 profiling. 173 174 /memory/classes/total:bytes 175 All memory mapped by the Go runtime into the current process 176 as read-write. Note that this does not include memory mapped 177 by code called via cgo or via the syscall package. 178 Sum of all metrics in /memory/classes. 179 180 /sched/gomaxprocs:threads 181 The current runtime.GOMAXPROCS setting, or the number of 182 operating system threads that can execute user-level Go code 183 simultaneously. 184 185 /sched/goroutines:goroutines 186 Count of live goroutines. 187 188 /sched/latencies:seconds 189 Distribution of the time goroutines have spent in the scheduler 190 in a runnable state before actually running. 191 */ 192 package metrics 193