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go/src/runtime/metrics/doc.go
Russ Cox 14ab998f95 cmd/go: add check for unknown godebug setting 
A //go:debug line mentioning an unknown or retired setting
should be diagnosed as making the program invalid. Do that.
We agreed on this in the proposal but I forgot to implement it.

Change-Id: Ie69072a1682d4eeb6866c02adbbb426f608567c4
Reviewed-on: https://go-review.googlesource.com/c/go/+/476280
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
2023-04-18 13:19:19 +00:00

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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.
// Note: run 'go generate' (which will run 'go test -generate') to update the "Supported metrics" list.
//go:generate go test -run=Docs -generate
/*
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.
/godebug/non-default-behavior/execerrdot:events
The number of non-default behaviors executed by the os/exec
package due to a non-default GODEBUG=execerrdot=... setting.
/godebug/non-default-behavior/http2client:events
The number of non-default behaviors executed by the net/http
package due to a non-default GODEBUG=http2client=... setting.
/godebug/non-default-behavior/http2server:events
The number of non-default behaviors executed by the net/http
package due to a non-default GODEBUG=http2server=... setting.
/godebug/non-default-behavior/installgoroot:events
The number of non-default behaviors executed by the go/build
package due to a non-default GODEBUG=installgoroot=... setting.
/godebug/non-default-behavior/jstmpllitinterp:events
The number of non-default behaviors executed by
the html/template package due to a non-default
GODEBUG=jstmpllitinterp=... setting.
/godebug/non-default-behavior/multipartmaxheaders:events
The number of non-default behaviors executed by
the mime/multipart package due to a non-default
GODEBUG=multipartmaxheaders=... setting.
/godebug/non-default-behavior/multipartmaxparts:events
The number of non-default behaviors executed by
the mime/multipart package due to a non-default
GODEBUG=multipartmaxparts=... setting.
/godebug/non-default-behavior/panicnil:events
The number of non-default behaviors executed by the runtime
package due to a non-default GODEBUG=panicnil=... setting.
/godebug/non-default-behavior/randautoseed:events
The number of non-default behaviors executed by the math/rand
package due to a non-default GODEBUG=randautoseed=... setting.
/godebug/non-default-behavior/tarinsecurepath:events
The number of non-default behaviors executed by the archive/tar
package due to a non-default GODEBUG=tarinsecurepath=...
setting.
/godebug/non-default-behavior/x509sha1:events
The number of non-default behaviors executed by the crypto/x509
package due to a non-default GODEBUG=x509sha1=... setting.
/godebug/non-default-behavior/x509usefallbackroots:events
The number of non-default behaviors executed by the crypto/x509
package due to a non-default GODEBUG=x509usefallbackroots=...
setting.
/godebug/non-default-behavior/zipinsecurepath:events
The number of non-default behaviors executed by the archive/zip
package due to a non-default GODEBUG=zipinsecurepath=...
setting.
/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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