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 runtime/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" (see ValueKind) 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."
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 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 /sched/pauses/total/gc: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/gogc:percent
Heap size target percentage configured by the user, otherwise
100. This value is set by the GOGC environment variable, and the
runtime/debug.SetGCPercent function.
/gc/gomemlimit:bytes
Go runtime memory limit configured by the user, otherwise
math.MaxInt64. This value is set by the GOMEMLIMIT environment
variable, and the runtime/debug.SetMemoryLimit function.
/gc/heap/allocs-by-size:bytes
Distribution of heap allocations by approximate size.
Bucket counts increase monotonically. 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.
Bucket counts increase monotonically. 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/live:bytes
Heap memory occupied by live objects that were marked by the
previous GC.
/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
Deprecated. Prefer the identical /sched/pauses/total/gc:seconds.
/gc/scan/globals:bytes
The total amount of global variable space that is scannable.
/gc/scan/heap:bytes
The total amount of heap space that is scannable.
/gc/scan/stack:bytes
The number of bytes of stack that were scanned last GC cycle.
/gc/scan/total:bytes
The total amount space that is scannable. Sum of all metrics in
/gc/scan.
/gc/stack/starting-size:bytes
The stack size of new goroutines.
/godebug/non-default-behavior/asynctimerchan:events
The number of non-default behaviors executed by the time package
due to a non-default GODEBUG=asynctimerchan=... setting.
/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/gocachehash:events
The number of non-default behaviors executed by the cmd/go
package due to a non-default GODEBUG=gocachehash=... setting.
/godebug/non-default-behavior/gocachetest:events
The number of non-default behaviors executed by the cmd/go
package due to a non-default GODEBUG=gocachetest=... setting.
/godebug/non-default-behavior/gocacheverify:events
The number of non-default behaviors executed by the cmd/go
package due to a non-default GODEBUG=gocacheverify=... setting.
/godebug/non-default-behavior/gotypesalias:events
The number of non-default behaviors executed by the go/types
package due to a non-default GODEBUG=gotypesalias=... 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/httplaxcontentlength:events
The number of non-default behaviors executed by the net/http
package due to a non-default GODEBUG=httplaxcontentlength=...
setting.
/godebug/non-default-behavior/httpmuxgo121:events
The number of non-default behaviors executed by the net/http
package due to a non-default GODEBUG=httpmuxgo121=... setting.
/godebug/non-default-behavior/httpservecontentkeepheaders:events
The number of non-default behaviors executed
by the net/http package due to a non-default
GODEBUG=httpservecontentkeepheaders=... 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/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/multipathtcp:events
The number of non-default behaviors executed by the net package
due to a non-default GODEBUG=multipathtcp=... setting.
/godebug/non-default-behavior/netedns0:events
The number of non-default behaviors executed by the net package
due to a non-default GODEBUG=netedns0=... 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/tls10server:events
The number of non-default behaviors executed by the crypto/tls
package due to a non-default GODEBUG=tls10server=... setting.
/godebug/non-default-behavior/tls3des:events
The number of non-default behaviors executed by the crypto/tls
package due to a non-default GODEBUG=tls3des=... setting.
/godebug/non-default-behavior/tlsmaxrsasize:events
The number of non-default behaviors executed by the crypto/tls
package due to a non-default GODEBUG=tlsmaxrsasize=... setting.
/godebug/non-default-behavior/tlsrsakex:events
The number of non-default behaviors executed by the crypto/tls
package due to a non-default GODEBUG=tlsrsakex=... setting.
/godebug/non-default-behavior/tlsunsafeekm:events
The number of non-default behaviors executed by the crypto/tls
package due to a non-default GODEBUG=tlsunsafeekm=... setting.
/godebug/non-default-behavior/winreadlinkvolume:events
The number of non-default behaviors executed by the os package
due to a non-default GODEBUG=winreadlinkvolume=... setting.
/godebug/non-default-behavior/winsymlink:events
The number of non-default behaviors executed by the os package
due to a non-default GODEBUG=winsymlink=... setting.
/godebug/non-default-behavior/x509keypairleaf:events
The number of non-default behaviors executed by the crypto/tls
package due to a non-default GODEBUG=x509keypairleaf=...
setting.
/godebug/non-default-behavior/x509negativeserial:events
The number of non-default behaviors executed by the crypto/x509
package due to a non-default GODEBUG=x509negativeserial=...
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/x509usepolicies:events
The number of non-default behaviors executed by the crypto/x509
package due to a non-default GODEBUG=x509usepolicies=...
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. Currently, this
represents all stack memory for goroutines. It also includes all
OS thread stacks in non-cgo programs. Note that stacks may be
allocated differently in the future, and this may change.
/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.
In non-cgo programs this metric is currently zero. This may
change in the future.In cgo programs this metric includes
OS thread stacks allocated directly from the OS. Currently,
this only accounts for one stack in c-shared and c-archive build
modes, and other sources of stacks from the OS are not measured.
This too may change in the future.
/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. Bucket counts
increase monotonically.
/sched/pauses/stopping/gc:seconds
Distribution of individual GC-related stop-the-world stopping
latencies. This is the time it takes from deciding to stop the
world until all Ps are stopped. This is a subset of the total
GC-related stop-the-world time (/sched/pauses/total/gc:seconds).
During this time, some threads may be executing. Bucket counts
increase monotonically.
/sched/pauses/stopping/other:seconds
Distribution of individual non-GC-related stop-the-world
stopping latencies. This is the time it takes from deciding
to stop the world until all Ps are stopped. This is a
subset of the total non-GC-related stop-the-world time
(/sched/pauses/total/other:seconds). During this time, some
threads may be executing. Bucket counts increase monotonically.
/sched/pauses/total/gc:seconds
Distribution of individual GC-related stop-the-world pause
latencies. This is the time from deciding to stop the world
until the world is started again. Some of this time is spent
getting all threads to stop (this is measured directly in
/sched/pauses/stopping/gc:seconds), during which some threads
may still be running. Bucket counts increase monotonically.
/sched/pauses/total/other:seconds
Distribution of individual non-GC-related stop-the-world
pause latencies. This is the time from deciding to stop the
world until the world is started again. Some of this time
is spent getting all threads to stop (measured directly in
/sched/pauses/stopping/other:seconds). Bucket counts increase
monotonically.
/sync/mutex/wait/total:seconds
Approximate cumulative time goroutines have spent blocked on a
sync.Mutex, sync.RWMutex, or runtime-internal lock. 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.