les: historical data garbage collection (#19570)

This change introduces garbage collection for the light client. Historical
chain data is deleted periodically. If you want to disable the GC, use
the --light.nopruning flag.

les/pruner.go

@@ -0,0 +1,98 @@
+// Copyright 2019 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library 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 Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package les
+
+import (
+	"sync"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common/math"
+	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/ethdb"
+	"github.com/ethereum/go-ethereum/log"
+)
+
+// pruner is responsible for pruning historical light chain data.
+type pruner struct {
+	db       ethdb.Database
+	indexers []*core.ChainIndexer
+	closeCh  chan struct{}
+	wg       sync.WaitGroup
+}
+
+// newPruner returns a light chain pruner instance.
+func newPruner(db ethdb.Database, indexers ...*core.ChainIndexer) *pruner {
+	pruner := &pruner{
+		db:       db,
+		indexers: indexers,
+		closeCh:  make(chan struct{}),
+	}
+	pruner.wg.Add(1)
+	go pruner.loop()
+	return pruner
+}
+
+// close notifies all background goroutines belonging to pruner to exit.
+func (p *pruner) close() {
+	close(p.closeCh)
+	p.wg.Wait()
+}
+
+// loop periodically queries the status of chain indexers and prunes useless
+// historical chain data. Notably, whenever Geth restarts, it will iterate
+// all historical sections even they don't exist at all(below checkpoint) so
+// that light client can prune cached chain data that was ODRed after pruning
+// that section.
+func (p *pruner) loop() {
+	defer p.wg.Done()
+
+	// cleanTicker is the ticker used to trigger a history clean 2 times a day.
+	var cleanTicker = time.NewTicker(12 * time.Hour)
+
+	// pruning finds the sections that have been processed by all indexers
+	// and deletes all historical chain data.
+	// Note, if some indexers don't support pruning(e.g. eth.BloomIndexer),
+	// pruning operations can be silently ignored.
+	pruning := func() {
+		min := uint64(math.MaxUint64)
+		for _, indexer := range p.indexers {
+			sections, _, _ := indexer.Sections()
+			if sections < min {
+				min = sections
+			}
+		}
+		// Always keep the latest section data in database.
+		if min < 2 || len(p.indexers) == 0 {
+			return
+		}
+		for _, indexer := range p.indexers {
+			if err := indexer.Prune(min - 2); err != nil {
+				log.Debug("Failed to prune historical data", "err", err)
+				return
+			}
+		}
+		p.db.Compact(nil, nil) // Compact entire database, ensure all removed data are deleted.
+	}
+	for {
+		pruning()
+		select {
+		case <-cleanTicker.C:
+		case <-p.closeCh:
+			return
+		}
+	}
+}