merge_shards.go

/*
 * Copyright (C) 2017 Dgraph Labs, Inc. and Contributors
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package bulk

import (
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"github.com/dgraph-io/dgraph/x"
)

func mergeMapShardsIntoReduceShards(opt options) {
	mapShards := shardDirs(opt.TmpDir)

	var reduceShards []string
	for i := 0; i < opt.ReduceShards; i++ {
		shardDir := filepath.Join(opt.TmpDir, "shards", fmt.Sprintf("shard_%d", i))
		x.Check(os.MkdirAll(shardDir, 0755))
		reduceShards = append(reduceShards, shardDir)
	}

	// Heuristic: put the largest map shard into the smallest reduce shard
	// until there are no more map shards left. Should be a good approximation.
	for _, shard := range mapShards {
		sortBySize(reduceShards)
		x.Check(os.Rename(shard, filepath.Join(
			reduceShards[len(reduceShards)-1], filepath.Base(shard))))
	}
}

func shardDirs(tmpDir string) []string {
	dir, err := os.Open(filepath.Join(tmpDir, "shards"))
	x.Check(err)
	shards, err := dir.Readdirnames(0)
	x.Check(err)
	dir.Close()
	for i, shard := range shards {
		shards[i] = filepath.Join(tmpDir, "shards", shard)
	}

	// Allow largest shards to be shuffled first.
	sortBySize(shards)
	return shards
}

func filenamesInTree(dir string) []string {
	var fnames []string
	x.Check(filepath.Walk(dir, func(path string, fi os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if strings.HasSuffix(path, ".map") {
			fnames = append(fnames, path)
		}
		return nil
	}))
	return fnames
}

type sizedDir struct {
	dir string
	sz  int64
}

// sortBySize sorts the input directories by size of their content (biggest to smallest).
func sortBySize(dirs []string) {
	sizedDirs := make([]sizedDir, len(dirs))
	for i, dir := range dirs {
		sizedDirs[i] = sizedDir{dir: dir, sz: treeSize(dir)}
	}
	sort.SliceStable(sizedDirs, func(i, j int) bool {
		return sizedDirs[i].sz > sizedDirs[j].sz
	})
	for i := range sizedDirs {
		dirs[i] = sizedDirs[i].dir
	}
}

func treeSize(dir string) int64 {
	var sum int64
	x.Check(filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		sum += info.Size()
		return nil
	}))
	return sum
}