database: Use an estimator in Cayley's Size() w/ PostgreSQL

Godeps/Godeps.json

@@ -42,7 +42,7 @@
 		{
 			"ImportPath": "github.com/google/cayley",
 			"Comment": "v0.4.1-160-gcdf0154",
-			"Rev": "cdf0154d1a34019651eb4f46ce666b31f4d8cae7"
+			"Rev": "6027e4c48b3385307bd4bea462149fd544577165"
 		},
 		{
 			"ImportPath": "github.com/julienschmidt/httprouter",

database/database.go

@@ -21,9 +21,9 @@ import (
 	"os"
 
 	"github.com/barakmich/glog"
-	"github.com/coreos/pkg/capnslog"
 	"github.com/coreos/clair/health"
 	"github.com/coreos/clair/utils"
+	"github.com/coreos/pkg/capnslog"
 	"github.com/google/cayley"
 	"github.com/google/cayley/graph"
 	"github.com/google/cayley/graph/path"
@@ -70,23 +70,29 @@ func Open(dbType, dbPath string) error {
 	}
 
 	var err error
+	options := make(graph.Options)
 
-	// Try to create database if necessary
-	if dbType == "bolt" || dbType == "leveldb" {
+	switch dbType {
+	case "bolt", "leveldb":
 		if _, err := os.Stat(dbPath); os.IsNotExist(err) {
-			// No, initialize it if possible
 			log.Infof("database at %s does not exist yet, creating it", dbPath)
 
-			if err = graph.InitQuadStore(dbType, dbPath, nil); err != nil {
+			err = graph.InitQuadStore(dbType, dbPath, options)
+			if err != nil {
 				log.Errorf("could not create database at %s : %s", dbPath, err)
 				return ErrCantOpen
 			}
 		}
-	} else if dbType == "sql" {
-		graph.InitQuadStore(dbType, dbPath, nil)
+	case "sql":
+		// Replaces the PostgreSQL's slow COUNT query with a fast estimator.
+		// See:
+		// Ref: https://wiki.postgresql.org/wiki/Count_estimate
+		options["use_estimates"] = true
+
+		graph.InitQuadStore(dbType, dbPath, options)
 	}
 
-	store, err = cayley.NewGraph(dbType, dbPath, nil)
+	store, err = cayley.NewGraph(dbType, dbPath, options)
 	if err != nil {
 		log.Errorf("could not open database at %s : %s", dbPath, err)
 		return ErrCantOpen

vendor/github.com/google/cayley/graph/sql/quadstore.go

@@ -37,11 +37,12 @@ var (
 )
 
 type QuadStore struct {
-	db        *sql.DB
-	sqlFlavor string
-	size      int64
-	lru       *cache
-	noSizes   bool
+	db           *sql.DB
+	sqlFlavor    string
+	size         int64
+	lru          *cache
+	noSizes      bool
+	useEstimates bool
 }
 
 func connectSQLTables(addr string, _ graph.Options) (*sql.DB, error) {
@@ -132,6 +133,11 @@ func newQuadStore(addr string, options graph.Options) (graph.QuadStore, error) {
 			qs.noSizes = false
 		}
 	}
+	qs.useEstimates, _, err = options.BoolKey("use_estimates")
+	if err != nil {
+		return nil, err
+	}
+
 	return &qs, nil
 }
 
@@ -286,7 +292,18 @@ func (qs *QuadStore) Size() int64 {
 	if qs.size != -1 {
 		return qs.size
 	}
-	c := qs.db.QueryRow("SELECT COUNT(*) FROM quads;")
+
+	query := "SELECT COUNT(*) FROM quads;"
+	if qs.useEstimates {
+		switch qs.sqlFlavor {
+		case "postgres":
+			query = "SELECT reltuples::BIGINT AS estimate FROM pg_class WHERE relname='quads';"
+		default:
+			panic("no estimate support for flavor: " + qs.sqlFlavor)
+		}
+	}
+
+	c := qs.db.QueryRow(query)
 	err := c.Scan(&qs.size)
 	if err != nil {
 		glog.Errorf("Couldn't execute COUNT: %v", err)