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 /gc/cycles/automatic:gc-cycles 55 Count of completed GC cycles generated by the Go runtime. 56 57 /gc/cycles/forced:gc-cycles 58 Count of completed GC cycles forced by the application. 59 60 /gc/cycles/total:gc-cycles 61 Count of all completed GC cycles. 62 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, 66 only tiny blocks. 67 68 /gc/heap/allocs:bytes 69 Cumulative sum of memory allocated to the heap by the application. 70 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, 74 only tiny blocks. 75 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, 79 only tiny blocks. 80 81 /gc/heap/frees:bytes 82 Cumulative sum of heap memory freed by the garbage collector. 83 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, 87 only tiny blocks. 88 89 /gc/heap/goal:bytes 90 Heap size target for the end of the GC cycle. 91 92 /gc/heap/objects:objects 93 Number of objects, live or unswept, occupying heap memory. 94 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. 101 102 /gc/pauses:seconds 103 Distribution individual GC-related stop-the-world pause latencies. 104 105 /memory/classes/heap/free:bytes 106 Memory that is completely free and eligible to be returned to 107 the underlying system, but has not been. This metric is the 108 runtime's estimate of free address space that is backed by 109 physical memory. 110 111 /memory/classes/heap/objects:bytes 112 Memory occupied by live objects and dead objects that have 113 not yet been marked free by the garbage collector. 114 115 /memory/classes/heap/released:bytes 116 Memory that is completely free and has been returned to 117 the underlying system. This metric is the runtime's estimate of 118 free address space that is still mapped into the process, but 119 is not backed by physical memory. 120 121 /memory/classes/heap/stacks:bytes 122 Memory allocated from the heap that is reserved for stack 123 space, whether or not it is currently in-use. 124 125 /memory/classes/heap/unused:bytes 126 Memory that is reserved for heap objects but is not currently 127 used to hold heap objects. 128 129 /memory/classes/metadata/mcache/free:bytes 130 Memory that is reserved for runtime mcache structures, but 131 not in-use. 132 133 /memory/classes/metadata/mcache/inuse:bytes 134 Memory that is occupied by runtime mcache structures that 135 are currently being used. 136 137 /memory/classes/metadata/mspan/free:bytes 138 Memory that is reserved for runtime mspan structures, but 139 not in-use. 140 141 /memory/classes/metadata/mspan/inuse:bytes 142 Memory that is occupied by runtime mspan structures that are 143 currently being used. 144 145 /memory/classes/metadata/other:bytes 146 Memory that is reserved for or used to hold runtime 147 metadata. 148 149 /memory/classes/os-stacks:bytes 150 Stack memory allocated by the underlying operating system. 151 152 /memory/classes/other:bytes 153 Memory used by execution trace buffers, structures for 154 debugging the runtime, finalizer and profiler specials, and 155 more. 156 157 /memory/classes/profiling/buckets:bytes 158 Memory that is used by the stack trace hash map used for 159 profiling. 160 161 /memory/classes/total:bytes 162 All memory mapped by the Go runtime into the current process 163 as read-write. Note that this does not include memory mapped 164 by code called via cgo or via the syscall package. 165 Sum of all metrics in /memory/classes. 166 167 /sched/goroutines:goroutines 168 Count of live goroutines. 169 170 /sched/latencies:seconds 171 Distribution of the time goroutines have spent in the scheduler 172 in a runnable state before actually running. 173 */ 174 package metrics 175