Macro imetric 

macro_rules! imetric {
    (target: $target:expr, $name:expr, $unit:expr, $($rest:tt)+) => { ... };
    ($name:expr, $unit:expr, $($rest:tt)+) => { ... };
}

Records a integer metric. Use [imetric_dyn!] when the name or unit is built at run time.

Examples

use micromegas_tracing::imetric;

imetric!("Frame Time", "ticks", 1000);

Properties go between the unit and the value, as key = value pairs. A key is an identifier or a string literal. Literal values are interned once per callsite, unless a ..set is spread without a static value, in which case the literals are copied into the block (the spread set’s own values are not); any other value is attached to the measure and copied into the current block. A bare value must implement PropertyValue (strings do); use %value (Display) or ?value (Debug) for the rest, at the cost of one String allocation.

use micromegas_tracing::prelude::*;

let correlation_id = String::from("c0ffee");
let rows = 3;
imetric!("rows_fetched", "count", correlation_id = correlation_id, region = "eu", rows = %rows, 3);
imetric!("rows_fetched", "count", "http.method" = "GET", 3);

A precomputed &'static PropertySet is spread with ..set. It must come last in the property list, and key = value pairs override its entries:

use micromegas_tracing::prelude::*;
use micromegas_tracing::property_set::{Property, PropertySet};

let set = PropertySet::find_or_create(vec![Property::new("region", "eu")]);
imetric!("rows_fetched", "count", ..set, 3);
imetric!("rows_fetched", "count", correlation_id = "c0ffee", ..set, 3);

target: "name" replaces the module path as the target of the metric:

use micromegas_tracing::prelude::*;

imetric!(target: "my_crate::cache", "hits", "count", kind = "disk", 1);

key = static expr takes a &'static str chosen at runtime, from a small closed set (a label or an enum variant name, for example). Each distinct tuple of static values is interned once per callsite and then looked up, a few nanoseconds more than a ..set spread and far cheaper than a dynamic value. Every distinct value is kept forever, so the cardinality contract of PropertySet applies: never use it for ids. It mixes freely with literals, dynamic values and a trailing ..set. Among literals and static values the last one wins (case-insensitive), a dynamic value beats both, and any pair overrides a ..set entry. With ..set and a static value in the same call, literals and static values are interned over the set, so dynamic values beat them whatever the order.

use micromegas_tracing::prelude::*;

let label: &'static str = "alpha";
imetric!("rows_fetched", "count", prefix = static label, tier = "ram", 3);
fmetric!("fetch_ms", "ms", prefix = static label, 1.5);

The value must be 'static; a borrowed string is a compile error:

use micromegas_tracing::prelude::*;

let s = String::from("alpha");
imetric!("rows_fetched", "count", prefix = static s.as_str(), 3);

static doesn’t combine with % or ?:

use micromegas_tracing::prelude::*;

imetric!("rows_fetched", "count", prefix = static %"x", 3);

target, name and unit are reserved keys, because analytics treats them as column overrides. They can still be set through a ..set spread:

use micromegas_tracing::prelude::*;

imetric!("rows_fetched", "count", unit = "rows", 3);

A literal value goes through concat!, so 1_000 is recorded as “1000” and 0x10 as “16”, while a float keeps its spelling (0.50 stays “0.50”); %value uses Display instead.

A bare integer needs %:

use micromegas_tracing::prelude::*;

let n = 3_u32;
imetric!("rows_fetched", "count", rows = n, 3);

A bare negated expression has no PropertyValue impl either:

use micromegas_tracing::prelude::*;

let n = 3_i32;
imetric!("rows_fetched", "count", delta = -n, 3);

..set can’t be followed by other entries, and appears at most once:

use micromegas_tracing::prelude::*;
use micromegas_tracing::property_set::PropertySet;

let set = PropertySet::empty();
imetric!("rows_fetched", "count", ..set, kind = "a", 3);

use micromegas_tracing::prelude::*;
use micromegas_tracing::property_set::PropertySet;

let set = PropertySet::empty();
imetric!("rows_fetched", "count", ..set, ..set, 3);