add per call stats field as histogram (#528)

* add per call stats field as histogram

this will add a histogram of up to 240 data points of call data, produced
every second, stored at the end of a call invocation in the db. the same
metrics are also still shipped to prometheus (prometheus has the
not-potentially-reduced version). for the API reference, see the updates to
the swagger spec, this is just added onto the get call endpoint.

this does not add any extra db calls and the field for stats in call is a json
blob, which is easily modified to add / omit future fields. this is just
tacked on to the call we're making to InsertCall, and expect this to add very
little overhead; we are bounding the set to be relatively small, planning to
clean out the db of calls periodically, functions will generally be short, and
the same code used at a previous firm did not cause a notable db size increase
with production workload that is worse, wrt histogram size (I checked). the
code changes are really small aside from changing to strfmt.DateTime,
adding a migration and implementing sql.Valuer; needed to slightly modify the
swap function so that we can safely read `call.Stats` field to upload at end.

with the full histogram in hand, we can compute max/min/average/median/growth
rate/bernoulli distributions/whatever very easily in a UI or tooling. in
particular, this data is easily chartable [for a UI], which is beneficial.

* adds swagger spec of api update to calls endpoint
* adds migration for call.stats field
* adds call.stats field to sql queries
* change swapping of hot logger to exec, so we know that call.Stats is no
longer being modified after `exec` [in call.End]
* throws out docker stats between function invocations in hot functions (no
call to store them on, we could change this later for debug; they're in prom)
* tested in tests and API

closes #19

* add format of ints to swag

api/agent/drivers/driver.go

@@ -3,10 +3,16 @@
 package drivers
 
 import (
+	"bytes"
 	"context"
+	"database/sql/driver"
+	"encoding/json"
+	"fmt"
 	"io"
 	"strings"
 	"time"
+
+	"github.com/go-openapi/strfmt"
 )
 
 // A DriverCookie identifies a unique request to run a task.
@@ -109,8 +115,50 @@ type ContainerTask interface {
 
 // Stat is a bucket of stats from a driver at a point in time for a certain task.
 type Stat struct {
-	Timestamp time.Time
-	Metrics   map[string]uint64
+	Timestamp strfmt.DateTime   `json:"timestamp"`
+	Metrics   map[string]uint64 `json:"metrics"`
+}
+
+// Stats is a list of Stat, notably implements sql.Valuer
+type Stats []Stat
+
+// implements sql.Valuer, returning a string
+func (s Stats) Value() (driver.Value, error) {
+	if len(s) < 1 {
+		return driver.Value(string("")), nil
+	}
+	var b bytes.Buffer
+	err := json.NewEncoder(&b).Encode(s)
+	// return a string type
+	return driver.Value(b.String()), err
+}
+
+// implements sql.Scanner
+func (s *Stats) Scan(value interface{}) error {
+	if value == nil {
+		*s = nil
+		return nil
+	}
+	bv, err := driver.String.ConvertValue(value)
+	if err == nil {
+		var b []byte
+		switch x := bv.(type) {
+		case []byte:
+			b = x
+		case string:
+			b = []byte(x)
+		}
+
+		if len(b) > 0 {
+			return json.Unmarshal(b, s)
+		}
+
+		*s = nil
+		return nil
+	}
+
+	// otherwise, return an error
+	return fmt.Errorf("stats invalid db format: %T %T value, err: %v", value, bv, err)
 }
 
 // TODO: ensure some type is applied to these statuses.
@@ -149,15 +197,15 @@ func average(samples []Stat) (Stat, bool) {
 	s := Stat{
 		Metrics: samples[0].Metrics, // Recycle Metrics map from first sample
 	}
-	t := samples[0].Timestamp.UnixNano() / int64(l)
+	t := time.Time(samples[0].Timestamp).UnixNano() / int64(l)
 	for _, sample := range samples[1:] {
-		t += sample.Timestamp.UnixNano() / int64(l)
+		t += time.Time(sample.Timestamp).UnixNano() / int64(l)
 		for k, v := range sample.Metrics {
 			s.Metrics[k] += v
 		}
 	}
 
-	s.Timestamp = time.Unix(0, t)
+	s.Timestamp = strfmt.DateTime(time.Unix(0, t))
 	for k, v := range s.Metrics {
 		s.Metrics[k] = v / uint64(l)
 	}
@@ -183,8 +231,8 @@ func Decimate(maxSamples int, stats []Stat) []Stat {
 		return nil
 	}
 
-	start := stats[0].Timestamp
-	window := stats[len(stats)-1].Timestamp.Sub(start) / time.Duration(maxSamples)
+	start := time.Time(stats[0].Timestamp)
+	window := time.Time(stats[len(stats)-1].Timestamp).Sub(start) / time.Duration(maxSamples)
 
 	nextEntry, current := 0, start // nextEntry is the index tracking next Stats record location
 	for x := 0; x < len(stats); {
@@ -192,7 +240,7 @@ func Decimate(maxSamples int, stats []Stat) []Stat {
 
 		var samples []Stat
 		for offset := 0; x+offset < len(stats); offset++ { // Iterate through samples until out of window
-			if !isLastEntry && stats[x+offset].Timestamp.After(current.Add(window)) {
+			if !isLastEntry && time.Time(stats[x+offset].Timestamp).After(current.Add(window)) {
 				break
 			}
 			samples = stats[x : x+offset+1]