observe

type Arm string

type Counter interface {
	// Add increases the counter by delta (never negative).
	Add(delta float64)
}

type Histogram interface {
	// Observe records one value.
	Observe(value float64)
}

type Hooks struct {
	// OnOperationStart fires before the operation does any work. The
	// context it returns (when non-nil) replaces the operation's context
	// for the work and for the matching OnPhase and OnOperationEnd
	// calls — the place to start a span.
	OnOperationStart func(ctx context.Context, info OperationInfo) context.Context
	// OnOperationEnd fires exactly once when the operation ends. A
	// streaming operation ends when its stream is drained, closed or its
	// context cancelled, whichever comes first; a stream the caller
	// leaks never ends.
	OnOperationEnd func(ctx context.Context, info OperationInfo, result OperationResult)
	// OnPhase reports the operation's phases: once per phase that ran,
	// in execution order, after the work finished and just before
	// OnOperationEnd. A phase that ran in several pieces (plan before
	// and after the cohort open) reports their sum. A streaming
	// operation's scan runs until the stream ends, so it includes the
	// time the consumer spends between reads.
	OnPhase func(ctx context.Context, info OperationInfo, phase PhaseTiming)
}

type Label struct {
	Key   string
	Value string
}

type Metrics interface {
	Counter(name string, labels ...Label) Counter
	Histogram(name string, labels ...Label) Histogram
	UpDownCounter(name string, labels ...Label) UpDownCounter
}

type OperationInfo struct {
	// Kind is the operation kind.
	Kind OperationKind
	// Scope is ScopeTop for a host call, ScopeChild for a slot or stage
	// Pulse fired inside another operation. A child carries its
	// parent's Kind (a Compose slot is a compose child).
	Scope Scope
	// ID identifies the operation within its Pulse instance; never 0.
	ID uint64
	// Parent is the ID of the enclosing operation for a child, 0 for a
	// top-level operation.
	Parent uint64
	// Index is the slot (Compose) or stage (ProcessChain) index of a
	// child operation; 0 for a top-level operation.
	Index int
	// Cohort is the cohort path the operation addresses, empty when it
	// addresses none.
	Cohort string
	// RequestHash is the canonical request hash (the request type's
	// Hash method), empty when the operation takes no request.
	RequestHash string
}

type OperationKind string

type OperationResult struct {
	// Duration is the wall time from start to end.
	Duration time.Duration
	// Code is CodeOK, the failing error's Pulse error code, or
	// CodeUncoded. It never carries an error message.
	Code string
	// RowsScanned is the number of records read.
	RowsScanned int64
	// RowsMatched is the number of records that passed the filters.
	RowsMatched int64
	// RowsOut is the number of result rows produced.
	RowsOut int64
	// BytesRead is the number of cohort bytes read.
	BytesRead int64
	// Shards is the number of shards read.
	Shards int
	// Workers is the number of workers the run used.
	Workers int
	// Arm is the execution arm the engine chose.
	Arm Arm
	// Projected reports whether a projected (field-subset) decode ran.
	Projected bool
}

type Phase string

type PhaseTiming struct {
	// Phase is the phase that finished.
	Phase Phase
	// Duration is its wall time.
	Duration time.Duration
}

type Scope string

type UpDownCounter interface {
	// Add changes the value by delta, positive or negative.
	Add(delta float64)
}