# `instrument`
[🔗](https://github.com/erlang/otp/blob/master/lib/runtime_tools/src/instrument.erl#L22)

Analysis and Utility Functions for Instrumentation

The module `instrument` contains support for studying the resource usage in an
Erlang runtime system. Currently, only the allocation of memory can be studied.

> #### Note {: .info }
>
> Since this module inspects internal details of the runtime system it may
> differ greatly from one version to another. We make no compatibility
> guarantees in this module.

## See Also

[erts_alloc(3)](`e:erts:erts_alloc.md`), [erl(1)](`e:erts:erl_cmd.md`)

# `allocation_origin`
*not exported* 

```elixir
-type allocation_origin() :: atom() | mfa() | pid() | port().
```

# `allocation_summary`
*not exported* 

```elixir
-type allocation_summary() ::
          {HistogramStart :: non_neg_integer(),
           UnscannedSize :: non_neg_integer(),
           Allocations :: #{Origin :: allocation_origin() => #{Type :: atom() => block_histogram()}}}.
```

A summary of allocated block sizes (including their headers) grouped by their
`Origin` and `Type`.

`Origin` is generally which NIF or driver that allocated the blocks, or 'system'
if it could not be determined.

`Type` is the allocation category that the blocks belong to, e.g. `db_term`,
`message` or `binary`. The categories correspond to those in
[erl_alloc.types](https://github.com/erlang/otp/blob/master/erts/emulator/beam/erl_alloc.types).

If one or more carriers could not be scanned in full without harming the
responsiveness of the system, `UnscannedSize` is the number of bytes that had to
be skipped.

# `block_histogram`
*not exported* 

```elixir
-type block_histogram() :: tuple().
```

A histogram of block sizes where each interval's upper bound is twice as high as
the one before it.

The upper bound of the first interval is provided by the function that returned
the histogram, and the last interval has no upper bound.

For example, the histogram below has 40 (`message`) blocks between 128-256 bytes
in size, 78 blocks between 256-512 bytes,2 blocks between 512-1024 bytes, and 2
blocks between 1-2KB.

```erlang
> instrument:allocations(#{ histogram_start => 128, histogram_width => 15 }).
{ok, {128, 0, #{ message => {0,40,78,2,2,0,0,0,0,0,0,0,0,0,0}, ... } }}
```

# `carrier_info_list`
*not exported* 

```elixir
-type carrier_info_list() ::
          {HistogramStart :: non_neg_integer(),
           Carriers ::
               [{AllocatorType :: atom(),
                 InPool :: boolean(),
                 TotalSize :: non_neg_integer(),
                 UnscannedSize :: non_neg_integer(),
                 Allocations ::
                     [{Type :: atom(), Count :: non_neg_integer(), Size :: non_neg_integer()}],
                 FreeBlocks :: block_histogram()}]}.
```

`AllocatorType` is the type of the allocator that employs this carrier.

`InPool` is whether the carrier is in the migration pool.

`TotalSize` is the total size of the carrier, including its header.

`Allocations` is a summary of the allocated blocks in the carrier. Note that
carriers may contain multiple different block types when carrier pools are
shared between different allocator types (see the
[`erts_alloc` ](`e:erts:erts_alloc.md#M_cp`)documentation for more details).

`FreeBlocks` is a histogram of the free block sizes in the carrier.

If the carrier could not be scanned in full without harming the responsiveness
of the system, `UnscannedSize` is the number of bytes that had to be skipped.

# `allocations`
*since OTP 21.0* 

```elixir
-spec allocations() -> {ok, Result} | {error, Reason}
                     when Result :: allocation_summary(), Reason :: not_enabled.
```

# `allocations`
*since OTP 21.0* 

```elixir
-spec allocations(Options) -> {ok, Result} | {error, Reason}
                     when
                         Result :: allocation_summary(),
                         Reason :: not_enabled,
                         Options ::
                             #{scheduler_ids => [non_neg_integer()],
                               allocator_types => [atom()],
                               histogram_start => pos_integer(),
                               histogram_width => pos_integer(),
                               flags => [per_process | per_port | per_mfa]}.
```

Returns a summary of all tagged allocations in the system, optionally filtered
by allocator type and scheduler id.

Only binaries and allocations made by NIFs and drivers are tagged by default,
but this can be configured an a per-allocator basis with the
[`+M<S>atags` ](`e:erts:erts_alloc.md#M_atags`)emulator option.

If the specified allocator types are not enabled, the call will fail with
`{error, not_enabled}`.

The following options can be used:

- **`allocator_types`** - The allocator types that will be searched.

  Specifying a specific allocator type may lead to strange results when carrier
  migration between different allocator types has been enabled: you may see
  unexpected types (e.g. process heaps when searching binary_alloc), or fewer
  blocks than expected if the carriers the blocks are on have been migrated out
  to an allocator of a different type.

  Defaults to all `alloc_util` allocators.

- **`scheduler_ids`** - The scheduler ids whose allocator instances will be
  searched. A scheduler id of 0 will refer to the global instance that is not
  tied to any particular scheduler. Defaults to all schedulers and the global
  instance.

- **`histogram_start`** - The upper bound of the first interval in the allocated
  block size histograms. Defaults to 128.

- **`histogram_width`** - The number of intervals in the allocated block size
  histograms. Defaults to 18.

- **`flags`** - Controls how to group the output, for example showing
  allocations on a per-process basis (when possible) rather than only a
  NIF/driver-basis. Defaults to `[]`.

_Example:_

```erlang
> instrument:allocations(#{ histogram_start => 128, histogram_width => 15 }).
{ok,{128,0,
     #{udp_inet =>
           #{driver_event_state => {0,0,0,0,0,0,0,0,0,1,0,0,0,0,0}},
       system =>
           #{heap => {0,0,0,0,20,4,2,2,2,3,0,1,0,0,1},
             db_term => {271,3,1,52,80,1,0,0,0,0,0,0,0,0,0},
             code => {0,0,0,5,3,6,11,22,19,20,10,2,1,0,0},
             binary => {18,0,0,0,7,0,0,1,0,0,0,0,0,0,0},
             message => {0,40,78,2,2,0,0,0,0,0,0,0,0,0,0},
             ... }
       spawn_forker =>
           #{driver_select_data_state =>
                 {1,0,0,0,0,0,0,0,0,0,0,0,0,0,0}},
       ram_file_drv => #{drv_binary => {0,0,0,0,0,0,1,0,0,0,0,0,0,0,0}},
       prim_file =>
           #{process_specific_data => {2,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
             nif_trap_export_entry => {0,4,0,0,0,0,0,0,0,0,0,0,0,0,0},
             monitor_extended => {0,1,0,0,0,0,0,0,0,0,0,0,0,0,0},
             drv_binary => {0,0,0,0,0,0,1,0,3,5,0,0,0,1,0},
             binary => {0,4,0,0,0,0,0,0,0,0,0,0,0,0,0}},
       prim_buffer =>
           #{nif_internal => {0,4,0,0,0,0,0,0,0,0,0,0,0,0,0},
             binary => {0,4,0,0,0,0,0,0,0,0,0,0,0,0,0}}}}}
```

# `carriers`
*since OTP 21.0* 

```elixir
-spec carriers() -> {ok, Result} | {error, Reason}
                  when Result :: carrier_info_list(), Reason :: not_enabled.
```

# `carriers`
*since OTP 21.0* 

```elixir
-spec carriers(Options) -> {ok, Result} | {error, Reason}
                  when
                      Result :: carrier_info_list(),
                      Reason :: not_enabled,
                      Options ::
                          #{scheduler_ids => [non_neg_integer()],
                            allocator_types => [atom()],
                            histogram_start => pos_integer(),
                            histogram_width => pos_integer()}.
```

Returns a summary of all carriers in the system, optionally filtered by
allocator type and scheduler id.

If the specified allocator types are not enabled, the call will fail with
`{error, not_enabled}`.

The following options can be used:

- **`allocator_types`** - The allocator types that will be searched. Defaults to
  all `alloc_util` allocators.

- **`scheduler_ids`** - The scheduler ids whose allocator instances will be
  searched. A scheduler id of 0 will refer to the global instance that is not
  tied to any particular scheduler. Defaults to all schedulers and the global
  instance.

- **`histogram_start`** - The upper bound of the first interval in the free
  block size histograms. Defaults to 512.

- **`histogram_width`** - The number of intervals in the free block size
  histograms. Defaults to 14.

_Example:_

```erlang
> instrument:carriers(#{ histogram_start => 512, histogram_width => 8 }).
{ok,{512,
     [{driver_alloc,false,262144,0,
                    [{driver_alloc,1,32784}],
                    {0,0,0,0,0,0,0,1}},
      {binary_alloc,false,32768,0,
                    [{binary_alloc,15,4304}],
                    {3,0,0,0,1,0,0,0}},
      {...}|...]}}
```

---

*Consult [api-reference.md](api-reference.md) for complete listing*
