doc.go

     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
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