github.com/geraldss/go/src@v0.0.0-20210511222824-ac7d0ebfc235/runtime/metrics/doc.go (about)

     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, 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?).
    21  
    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.
    28  
    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."
    33  
    34  Metric key format
    35  
    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.
    41  
    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.
    44  
    45  A note about floats
    46  
    47  This package supports metrics whose values have a floating-point representation. In
    48  order to improve ease-of-use, this package promises to never produce the following
    49  classes of floating-point values: NaN, infinity.
    50  
    51  Supported metrics
    52  
    53  Below is the full list of supported metrics, ordered lexicographically.
    54  
    55  	/gc/cycles/automatic:gc-cycles
    56  		Count of completed GC cycles generated by the Go runtime.
    57  
    58  	/gc/cycles/forced:gc-cycles
    59  		Count of completed GC cycles forced by the application.
    60  
    61  	/gc/cycles/total:gc-cycles
    62  		Count of all completed GC cycles.
    63  
    64  	/gc/heap/allocs-by-size:bytes
    65  		Distribution of all objects allocated by approximate size.
    66  
    67  	/gc/heap/frees-by-size:bytes
    68  		Distribution of all objects freed by approximate size.
    69  
    70  	/gc/heap/goal:bytes
    71  		Heap size target for the end of the GC cycle.
    72  
    73  	/gc/heap/objects:objects
    74  		Number of objects, live or unswept, occupying heap memory.
    75  
    76  	/gc/pauses:seconds
    77  		Distribution individual GC-related stop-the-world pause latencies.
    78  
    79  	/memory/classes/heap/free:bytes
    80  		Memory that is completely free and eligible to be returned to
    81  		the underlying system, but has not been. This metric is the
    82  		runtime's estimate of free address space that is backed by
    83  		physical memory.
    84  
    85  	/memory/classes/heap/objects:bytes
    86  		Memory occupied by live objects and dead objects that have
    87  		not yet been marked free by the garbage collector.
    88  
    89  	/memory/classes/heap/released:bytes
    90  		Memory that is completely free and has been returned to
    91  		the underlying system. This metric is the runtime's estimate of
    92  		free address space that is still mapped into the process, but
    93  		is not backed by physical memory.
    94  
    95  	/memory/classes/heap/stacks:bytes
    96  		Memory allocated from the heap that is reserved for stack
    97  		space, whether or not it is currently in-use.
    98  
    99  	/memory/classes/heap/unused:bytes
   100  		Memory that is reserved for heap objects but is not currently
   101  		used to hold heap objects.
   102  
   103  	/memory/classes/metadata/mcache/free:bytes
   104  		Memory that is reserved for runtime mcache structures, but
   105  		not in-use.
   106  
   107  	/memory/classes/metadata/mcache/inuse:bytes
   108  		Memory that is occupied by runtime mcache structures that
   109  		are currently being used.
   110  
   111  	/memory/classes/metadata/mspan/free:bytes
   112  		Memory that is reserved for runtime mspan structures, but
   113  		not in-use.
   114  
   115  	/memory/classes/metadata/mspan/inuse:bytes
   116  		Memory that is occupied by runtime mspan structures that are
   117  		currently being used.
   118  
   119  	/memory/classes/metadata/other:bytes
   120  		Memory that is reserved for or used to hold runtime
   121  		metadata.
   122  
   123  	/memory/classes/os-stacks:bytes
   124  		Stack memory allocated by the underlying operating system.
   125  
   126  	/memory/classes/other:bytes
   127  		Memory used by execution trace buffers, structures for
   128  		debugging the runtime, finalizer and profiler specials, and
   129  		more.
   130  
   131  	/memory/classes/profiling/buckets:bytes
   132  		Memory that is used by the stack trace hash map used for
   133  		profiling.
   134  
   135  	/memory/classes/total:bytes
   136  		All memory mapped by the Go runtime into the current process
   137  		as read-write. Note that this does not include memory mapped
   138  		by code called via cgo or via the syscall package.
   139  		Sum of all metrics in /memory/classes.
   140  
   141  	/sched/goroutines:goroutines
   142  		Count of live goroutines.
   143  */
   144  package metrics