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// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
/*
Package metrics provides a stable interface to access implementation-defined
metrics exported by the Go runtime. This package is similar to existing functions
like runtime.ReadMemStats and debug.ReadGCStats, but significantly more general.
The set of metrics defined by this package may evolve as the runtime itself
evolves, and also enables variation across Go implementations, whose relevant
metric sets may not intersect.
# Interface
Metrics are designated by a string key, rather than, for example, a field name in
a struct. The full list of supported metrics is always available in the slice of
Descriptions returned by All. Each Description also includes useful information
about the metric.
Thus, users of this API are encouraged to sample supported metrics defined by the
slice returned by All to remain compatible across Go versions. Of course, situations
arise where reading specific metrics is critical. For these cases, users are
encouraged to use build tags, and although metrics may be deprecated and removed,
users should consider this to be an exceptional and rare event, coinciding with a
very large change in a particular Go implementation.
Each metric key also has a "kind" that describes the format of the metric's value.
In the interest of not breaking users of this package, the "kind" for a given metric
is guaranteed not to change. If it must change, then a new metric will be introduced
with a new key and a new "kind."
# Metric key format
As mentioned earlier, metric keys are strings. Their format is simple and well-defined,
designed to be both human and machine readable. It is split into two components,
separated by a colon: a rooted path and a unit. The choice to include the unit in
the key is motivated by compatibility: if a metric's unit changes, its semantics likely
did also, and a new key should be introduced.
For more details on the precise definition of the metric key's path and unit formats, see
the documentation of the Name field of the Description struct.
# A note about floats
This package supports metrics whose values have a floating-point representation. In
order to improve ease-of-use, this package promises to never produce the following
classes of floating-point values: NaN, infinity.
# Supported metrics
Below is the full list of supported metrics, ordered lexicographically.
/cgo/go-to-c-calls:calls
Count of calls made from Go to C by the current process.
/cpu/classes/gc/mark/assist:cpu-seconds
Estimated total CPU time goroutines spent performing GC tasks
to assist the GC and prevent it from falling behind the application.
This metric is an overestimate, and not directly comparable to
system CPU time measurements. Compare only with other /cpu/classes
metrics.
/cpu/classes/gc/mark/dedicated:cpu-seconds
Estimated total CPU time spent performing GC tasks on
processors (as defined by GOMAXPROCS) dedicated to those tasks.
This includes time spent with the world stopped due to the GC.
This metric is an overestimate, and not directly comparable to
system CPU time measurements. Compare only with other /cpu/classes
metrics.
/cpu/classes/gc/mark/idle:cpu-seconds
Estimated total CPU time spent performing GC tasks on
spare CPU resources that the Go scheduler could not otherwise find
a use for. This should be subtracted from the total GC CPU time to
obtain a measure of compulsory GC CPU time.
This metric is an overestimate, and not directly comparable to
system CPU time measurements. Compare only with other /cpu/classes
metrics.
/cpu/classes/gc/pause:cpu-seconds
Estimated total CPU time spent with the application paused by
the GC. Even if only one thread is running during the pause, this is
computed as GOMAXPROCS times the pause latency because nothing else
can be executing. This is the exact sum of samples in /gc/pause:seconds
if each sample is multiplied by GOMAXPROCS at the time it is taken.
This metric is an overestimate, and not directly comparable to
system CPU time measurements. Compare only with other /cpu/classes
metrics.
/cpu/classes/gc/total:cpu-seconds
Estimated total CPU time spent performing GC tasks.
This metric is an overestimate, and not directly comparable to
system CPU time measurements. Compare only with other /cpu/classes
metrics. Sum of all metrics in /cpu/classes/gc.
/cpu/classes/idle:cpu-seconds
Estimated total available CPU time not spent executing any Go or Go
runtime code. In other words, the part of /cpu/classes/total:cpu-seconds
that was unused.
This metric is an overestimate, and not directly comparable to
system CPU time measurements. Compare only with other /cpu/classes
metrics.
/cpu/classes/scavenge/assist:cpu-seconds
Estimated total CPU time spent returning unused memory to the
underlying platform in response eagerly in response to memory pressure.
This metric is an overestimate, and not directly comparable to
system CPU time measurements. Compare only with other /cpu/classes
metrics.
/cpu/classes/scavenge/background:cpu-seconds
Estimated total CPU time spent performing background tasks
to return unused memory to the underlying platform.
This metric is an overestimate, and not directly comparable to
system CPU time measurements. Compare only with other /cpu/classes
metrics.
/cpu/classes/scavenge/total:cpu-seconds
Estimated total CPU time spent performing tasks that return
unused memory to the underlying platform.
This metric is an overestimate, and not directly comparable to
system CPU time measurements. Compare only with other /cpu/classes
metrics. Sum of all metrics in /cpu/classes/scavenge.
/cpu/classes/total:cpu-seconds
Estimated total available CPU time for user Go code or the Go runtime, as
defined by GOMAXPROCS. In other words, GOMAXPROCS integrated over the
wall-clock duration this process has been executing for.
This metric is an overestimate, and not directly comparable to
system CPU time measurements. Compare only with other /cpu/classes
metrics. Sum of all metrics in /cpu/classes.
/cpu/classes/user:cpu-seconds
Estimated total CPU time spent running user Go code. This may
also include some small amount of time spent in the Go runtime.
This metric is an overestimate, and not directly comparable to
system CPU time measurements. Compare only with other /cpu/classes
metrics.
/gc/cycles/automatic:gc-cycles
Count of completed GC cycles generated by the Go runtime.
/gc/cycles/forced:gc-cycles
Count of completed GC cycles forced by the application.
/gc/cycles/total:gc-cycles
Count of all completed GC cycles.
/gc/heap/allocs-by-size:bytes
Distribution of heap allocations by approximate size.
Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects,
only tiny blocks.
/gc/heap/allocs:bytes
Cumulative sum of memory allocated to the heap by the application.
/gc/heap/allocs:objects
Cumulative count of heap allocations triggered by the application.
Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects,
only tiny blocks.
/gc/heap/frees-by-size:bytes
Distribution of freed heap allocations by approximate size.
Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects,
only tiny blocks.
/gc/heap/frees:bytes
Cumulative sum of heap memory freed by the garbage collector.
/gc/heap/frees:objects
Cumulative count of heap allocations whose storage was freed by the garbage collector.
Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects,
only tiny blocks.
/gc/heap/goal:bytes
Heap size target for the end of the GC cycle.
/gc/heap/objects:objects
Number of objects, live or unswept, occupying heap memory.
/gc/heap/tiny/allocs:objects
Count of small allocations that are packed together into blocks.
These allocations are counted separately from other allocations
because each individual allocation is not tracked by the runtime,
only their block. Each block is already accounted for in
allocs-by-size and frees-by-size.
/gc/limiter/last-enabled:gc-cycle
GC cycle the last time the GC CPU limiter was enabled.
This metric is useful for diagnosing the root cause of an out-of-memory
error, because the limiter trades memory for CPU time when the GC's CPU
time gets too high. This is most likely to occur with use of SetMemoryLimit.
The first GC cycle is cycle 1, so a value of 0 indicates that it was never enabled.
/gc/pauses:seconds
Distribution individual GC-related stop-the-world pause latencies.
/gc/stack/starting-size:bytes
The stack size of new goroutines.
/memory/classes/heap/free:bytes
Memory that is completely free and eligible to be returned to
the underlying system, but has not been. This metric is the
runtime's estimate of free address space that is backed by
physical memory.
/memory/classes/heap/objects:bytes
Memory occupied by live objects and dead objects that have
not yet been marked free by the garbage collector.
/memory/classes/heap/released:bytes
Memory that is completely free and has been returned to
the underlying system. This metric is the runtime's estimate of
free address space that is still mapped into the process, but
is not backed by physical memory.
/memory/classes/heap/stacks:bytes
Memory allocated from the heap that is reserved for stack
space, whether or not it is currently in-use.
/memory/classes/heap/unused:bytes
Memory that is reserved for heap objects but is not currently
used to hold heap objects.
/memory/classes/metadata/mcache/free:bytes
Memory that is reserved for runtime mcache structures, but
not in-use.
/memory/classes/metadata/mcache/inuse:bytes
Memory that is occupied by runtime mcache structures that
are currently being used.
/memory/classes/metadata/mspan/free:bytes
Memory that is reserved for runtime mspan structures, but
not in-use.
/memory/classes/metadata/mspan/inuse:bytes
Memory that is occupied by runtime mspan structures that are
currently being used.
/memory/classes/metadata/other:bytes
Memory that is reserved for or used to hold runtime
metadata.
/memory/classes/os-stacks:bytes
Stack memory allocated by the underlying operating system.
/memory/classes/other:bytes
Memory used by execution trace buffers, structures for
debugging the runtime, finalizer and profiler specials, and
more.
/memory/classes/profiling/buckets:bytes
Memory that is used by the stack trace hash map used for
profiling.
/memory/classes/total:bytes
All memory mapped by the Go runtime into the current process
as read-write. Note that this does not include memory mapped
by code called via cgo or via the syscall package.
Sum of all metrics in /memory/classes.
/sched/gomaxprocs:threads
The current runtime.GOMAXPROCS setting, or the number of
operating system threads that can execute user-level Go code
simultaneously.
/sched/goroutines:goroutines
Count of live goroutines.
/sched/latencies:seconds
Distribution of the time goroutines have spent in the scheduler
in a runnable state before actually running.
/sync/mutex/wait/total:seconds
Approximate cumulative time goroutines have spent blocked on a
sync.Mutex or sync.RWMutex. This metric is useful for identifying
global changes in lock contention. Collect a mutex or block
profile using the runtime/pprof package for more detailed
contention data.
*/
package metrics
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