core: remove stale transfer entries, fix #2096

Initially I thought of doing it in the next persist cycle, but testing shows
that it needs just ~2-5% of the time MPT GC does, so doing it in the same
cycle doesn't affect anything.

pkg/core/blockchain.go

@@ -2,6 +2,7 @@ package core
 
 import (
 	"bytes"
+	"encoding/binary"
 	"errors"
 	"fmt"
 	"math"
@@ -704,6 +705,62 @@ func (bc *Blockchain) tryRunGC(old uint32) time.Duration {
 		tgtBlock /= int64(bc.config.GarbageCollectionPeriod)
 		tgtBlock *= int64(bc.config.GarbageCollectionPeriod)
 		dur = bc.stateRoot.GC(uint32(tgtBlock), bc.store)
+		dur += bc.removeOldTransfers(uint32(tgtBlock))
+	}
+	return dur
+}
+
+func (bc *Blockchain) removeOldTransfers(index uint32) time.Duration {
+	bc.log.Info("starting transfer data garbage collection", zap.Uint32("index", index))
+	start := time.Now()
+	h, err := bc.GetHeader(bc.GetHeaderHash(int(index)))
+	if err != nil {
+		dur := time.Since(start)
+		bc.log.Error("failed to find block header for transfer GC", zap.Duration("time", dur), zap.Error(err))
+		return dur
+	}
+	var removed, kept int64
+	var ts = h.Timestamp
+	prefixes := []byte{byte(storage.STNEP11Transfers), byte(storage.STNEP17Transfers)}
+
+	for i := range prefixes {
+		var acc util.Uint160
+		var canDrop bool
+
+		err = bc.store.SeekGC(storage.SeekRange{
+			Prefix:    prefixes[i : i+1],
+			Backwards: true, // From new to old.
+		}, func(k, v []byte) bool {
+			// We don't look inside of the batches, it requires too much effort, instead
+			// we drop batches that are confirmed to contain outdated entries.
+			var batchAcc util.Uint160
+			var batchTs = binary.BigEndian.Uint64(k[1+util.Uint160Size:])
+			copy(batchAcc[:], k[1:])
+
+			if batchAcc != acc { // Some new account we're iterating over.
+				acc = batchAcc
+			} else if canDrop { // We've seen this account and all entries in this batch are guaranteed to be outdated.
+				removed++
+				return false
+			}
+			// We don't know what's inside, so keep the current
+			// batch anyway, but allow to drop older ones.
+			canDrop = batchTs <= ts
+			kept++
+			return true
+		})
+		if err != nil {
+			break
+		}
+	}
+	dur := time.Since(start)
+	if err != nil {
+		bc.log.Error("failed to flush transfer data GC changeset", zap.Duration("time", dur), zap.Error(err))
+	} else {
+		bc.log.Info("finished transfer data garbage collection",
+			zap.Int64("removed", removed),
+			zap.Int64("kept", kept),
+			zap.Duration("time", dur))
 	}
 	return dur
 }

pkg/core/blockchain_test.go

@@ -1588,6 +1588,67 @@ func TestDumpAndRestore(t *testing.T) {
 	})
 }
 
+func TestRemoveOldTransfers(t *testing.T) {
+	// Creating proper number of transfers/blocks takes unneccessary time, so emulate
+	// some DB with stale entries.
+	bc := newTestChain(t)
+	h, err := bc.GetHeader(bc.GetHeaderHash(0))
+	require.NoError(t, err)
+	older := h.Timestamp - 1000
+	newer := h.Timestamp + 1000
+	acc1 := util.Uint160{1}
+	acc2 := util.Uint160{2}
+	acc3 := util.Uint160{3}
+	ttl := state.TokenTransferLog{Raw: []byte{1}} // It's incorrect, but who cares.
+
+	for i := uint32(0); i < 3; i++ {
+		require.NoError(t, bc.dao.PutTokenTransferLog(acc1, older, i, false, &ttl))
+	}
+	for i := uint32(0); i < 3; i++ {
+		require.NoError(t, bc.dao.PutTokenTransferLog(acc2, newer, i, false, &ttl))
+	}
+	for i := uint32(0); i < 2; i++ {
+		require.NoError(t, bc.dao.PutTokenTransferLog(acc3, older, i, true, &ttl))
+	}
+	for i := uint32(0); i < 2; i++ {
+		require.NoError(t, bc.dao.PutTokenTransferLog(acc3, newer, i, true, &ttl))
+	}
+
+	_, err = bc.dao.Persist()
+	require.NoError(t, err)
+	_ = bc.removeOldTransfers(0)
+
+	for i := uint32(0); i < 2; i++ {
+		log, err := bc.dao.GetTokenTransferLog(acc1, older, i, false)
+		require.NoError(t, err)
+		require.Equal(t, 0, len(log.Raw))
+	}
+
+	log, err := bc.dao.GetTokenTransferLog(acc1, older, 2, false)
+	require.NoError(t, err)
+	require.NotEqual(t, 0, len(log.Raw))
+
+	for i := uint32(0); i < 3; i++ {
+		log, err = bc.dao.GetTokenTransferLog(acc2, newer, i, false)
+		require.NoError(t, err)
+		require.NotEqual(t, 0, len(log.Raw))
+	}
+
+	log, err = bc.dao.GetTokenTransferLog(acc3, older, 0, true)
+	require.NoError(t, err)
+	require.Equal(t, 0, len(log.Raw))
+
+	log, err = bc.dao.GetTokenTransferLog(acc3, older, 1, true)
+	require.NoError(t, err)
+	require.NotEqual(t, 0, len(log.Raw))
+
+	for i := uint32(0); i < 2; i++ {
+		log, err = bc.dao.GetTokenTransferLog(acc3, newer, i, true)
+		require.NoError(t, err)
+		require.NotEqual(t, 0, len(log.Raw))
+	}
+}
+
 func TestRemoveUntraceable(t *testing.T) {
 	check := func(t *testing.T, bc *Blockchain, tHash, bHash, sHash util.Uint256, errorExpected bool) {
 		_, _, err := bc.GetTransaction(tHash)