first working-ish Postgres backend

Subcommits:

implement iterator and remove ResultTree

add Err() to sql

remove redundant and less helpful indices, change fillfactor, and use COPY FROM

graph/sql/iterator.go

@@ -0,0 +1,270 @@
+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sql
+
+import (
+	"database/sql"
+	"fmt"
+
+	"github.com/barakmich/glog"
+
+	"github.com/google/cayley/graph"
+	"github.com/google/cayley/graph/iterator"
+	"github.com/google/cayley/quad"
+)
+
+type Iterator struct {
+	uid    uint64
+	tags   graph.Tagger
+	qs     *QuadStore
+	dir    quad.Direction
+	val    graph.Value
+	size   int64
+	isAll  bool
+	table  string
+	cursor *sql.Rows
+	result graph.Value
+	err    error
+}
+
+func (it *Iterator) makeCursor() {
+	var cursor *sql.Rows
+	var err error
+	if it.cursor != nil {
+		it.cursor.Close()
+	}
+	if it.isAll {
+		if it.table == "quads" {
+			cursor, err = it.qs.db.Query(`SELECT subject, predicate, object, label FROM quads;`)
+			if err != nil {
+				glog.Errorln("Couldn't get cursor from SQL database: %v", err)
+				cursor = nil
+			}
+		} else {
+			glog.V(4).Infoln("sql: getting node query")
+			cursor, err = it.qs.db.Query(`SELECT node FROM
+			(
+				SELECT subject FROM quads
+				UNION
+				SELECT predicate FROM quads
+				UNION
+				SELECT object FROM quads
+				UNION
+				SELECT label FROM quads
+			) AS DistinctNodes (node) WHERE node IS NOT NULL;`)
+			if err != nil {
+				glog.Errorln("Couldn't get cursor from SQL database: %v", err)
+				cursor = nil
+			}
+			glog.V(4).Infoln("sql: got node query")
+		}
+	} else {
+		cursor, err = it.qs.db.Query(
+			fmt.Sprintf("SELECT subject, predicate, object, label FROM quads WHERE %s = $1;", it.dir.String()), it.val.(string))
+		if err != nil {
+			glog.Errorln("Couldn't get cursor from SQL database: %v", err)
+			cursor = nil
+		}
+	}
+	it.cursor = cursor
+}
+
+func NewIterator(qs *QuadStore, d quad.Direction, val graph.Value) *Iterator {
+	it := &Iterator{
+		uid:   iterator.NextUID(),
+		qs:    qs,
+		dir:   d,
+		size:  -1,
+		val:   val,
+		table: "quads",
+		isAll: false,
+	}
+	return it
+}
+
+func NewAllIterator(qs *QuadStore, table string) *Iterator {
+	var size int64
+	it := &Iterator{
+		uid:   iterator.NextUID(),
+		qs:    qs,
+		dir:   quad.Any,
+		size:  size,
+		table: table,
+		isAll: true,
+	}
+	return it
+}
+
+func (it *Iterator) UID() uint64 {
+	return it.uid
+}
+
+func (it *Iterator) Reset() {
+	it.err = nil
+	it.Close()
+}
+
+func (it *Iterator) Err() error {
+	return it.err
+}
+
+func (it *Iterator) Close() error {
+	if it.cursor != nil {
+		err := it.cursor.Close()
+		if err != nil {
+			return err
+		}
+		it.cursor = nil
+	}
+	return nil
+}
+
+func (it *Iterator) Tagger() *graph.Tagger {
+	return &it.tags
+}
+
+func (it *Iterator) TagResults(dst map[string]graph.Value) {
+	for _, tag := range it.tags.Tags() {
+		dst[tag] = it.Result()
+	}
+
+	for tag, value := range it.tags.Fixed() {
+		dst[tag] = value
+	}
+}
+
+func (it *Iterator) Clone() graph.Iterator {
+	var m *Iterator
+	if it.isAll {
+		m = NewAllIterator(it.qs, it.table)
+	} else {
+		m = NewIterator(it.qs, it.dir, it.val)
+	}
+	m.tags.CopyFrom(it)
+	return m
+}
+
+func (it *Iterator) SubIterators() []graph.Iterator {
+	return nil
+}
+
+func (it *Iterator) Next() bool {
+	graph.NextLogIn(it)
+	if it.cursor == nil {
+		it.makeCursor()
+	}
+	if !it.cursor.Next() {
+		glog.V(4).Infoln("sql: No next")
+		err := it.cursor.Err()
+		if err != nil {
+			glog.Errorf("Cursor error in SQL: %v", err)
+			it.err = err
+		}
+		it.cursor.Close()
+		return false
+	}
+	if it.table == "nodes" {
+		var node string
+		err := it.cursor.Scan(&node)
+		if err != nil {
+			glog.Errorf("Error nexting node iterator: %v", err)
+			it.err = err
+			return false
+		}
+		it.result = node
+		return true
+	}
+	var q quad.Quad
+	err := it.cursor.Scan(&q.Subject, &q.Predicate, &q.Object, &q.Label)
+	if err != nil {
+		glog.Errorf("Error scanning sql iterator: %v", err)
+		it.err = err
+		return false
+	}
+	it.result = q
+	return graph.NextLogOut(it, it.result, true)
+}
+
+func (it *Iterator) Contains(v graph.Value) bool {
+	graph.ContainsLogIn(it, v)
+	if it.isAll {
+		return graph.ContainsLogOut(it, v, true)
+	}
+	q := v.(quad.Quad)
+	if q.Get(it.dir) == it.val.(string) {
+		return graph.ContainsLogOut(it, v, true)
+	}
+	return graph.ContainsLogOut(it, v, false)
+}
+
+func (it *Iterator) Size() (int64, bool) {
+	if it.size != -1 {
+		return it.size, true
+	}
+	it.size = it.qs.sizeForIterator(it.isAll, it.dir, it.val.(string))
+	return it.size, true
+}
+
+func (it *Iterator) Result() graph.Value {
+	return it.result
+}
+
+func (it *Iterator) NextPath() bool {
+	return false
+}
+
+var sqlType graph.Type
+
+func init() {
+	sqlType = graph.RegisterIterator("sql")
+}
+
+func Type() graph.Type { return sqlType }
+
+func (it *Iterator) Type() graph.Type {
+	if it.isAll {
+		return graph.All
+	}
+	return sqlType
+}
+
+func (it *Iterator) Sorted() bool                     { return true }
+func (it *Iterator) Optimize() (graph.Iterator, bool) { return it, false }
+
+func (it *Iterator) Describe() graph.Description {
+	size, _ := it.Size()
+	return graph.Description{
+		UID:  it.UID(),
+		Name: fmt.Sprintf("%s/%s", it.val, it.dir),
+		Type: it.Type(),
+		Size: size,
+	}
+}
+
+func (it *Iterator) Stats() graph.IteratorStats {
+	size, _ := it.Size()
+	if it.table == "nodes" {
+		return graph.IteratorStats{
+			ContainsCost: 1,
+			NextCost:     9999,
+			Size:         size,
+		}
+	}
+	return graph.IteratorStats{
+		ContainsCost: 1,
+		NextCost:     5,
+		Size:         size,
+	}
+}