core: remove old blocks and transactions

Remove blocks with `height <= current height - MaxTraceableBlocks`
together with transactions.

pkg/config/protocol_config.go

@@ -13,6 +13,8 @@ type (
 		// If true, DB size will be smaller, but older roots won't be accessible.
 		// This value should remain the same for the same database.
 		KeepOnlyLatestState bool `yaml:"KeepOnlyLatestState"`
+		// RemoveUntraceableBlocks specifies if old blocks should be removed.
+		RemoveUntraceableBlocks bool `yaml:"RemoveUntraceableBlocks"`
 		// MaxTraceableBlocks is the length of the chain accessible to smart contracts.
 		MaxTraceableBlocks uint32 `yaml:"MaxTraceableBlocks"`
 		// P2PSigExtensions enables additional signature-related transaction attributes

pkg/core/blockchain.go

@@ -697,6 +697,18 @@ func (bc *Blockchain) storeBlock(block *block.Block, txpool *mempool.Pool) error
 	if bc.config.SaveStorageBatch {
 		bc.lastBatch = cache.DAO.GetBatch()
 	}
+	if bc.config.RemoveUntraceableBlocks {
+		if block.Index > bc.config.MaxTraceableBlocks {
+			index := block.Index - bc.config.MaxTraceableBlocks // is at least 1
+			err := cache.DeleteBlock(bc.headerHashes[index], writeBuf)
+			if err != nil {
+				bc.log.Warn("error while removing old block",
+					zap.Uint32("index", index),
+					zap.Error(err))
+			}
+			writeBuf.Reset()
+		}
+	}
 
 	bc.lock.Lock()
 	_, err = cache.Persist()

pkg/core/dao/dao.go

@@ -32,6 +32,7 @@ var (
 type DAO interface {
 	AppendAppExecResult(aer *state.AppExecResult, buf *io.BufBinWriter) error
 	AppendNEP17Transfer(acc util.Uint160, index uint32, tr *state.NEP17Transfer) (bool, error)
+	DeleteBlock(h util.Uint256, buf *io.BufBinWriter) error
 	DeleteContractState(hash util.Uint160) error
 	DeleteStorageItem(id int32, key []byte) error
 	GetAndDecode(entity io.Serializable, key []byte) error
@@ -672,6 +673,46 @@ func (dao *Simple) StoreAsBlock(block *block.Block, buf *io.BufBinWriter) error
 	return dao.Store.Put(key, buf.Bytes())
 }
 
+// DeleteBlock removes block from dao.
+func (dao *Simple) DeleteBlock(h util.Uint256, w *io.BufBinWriter) error {
+	batch := dao.Store.Batch()
+	key := make([]byte, util.Uint256Size+1)
+	key[0] = byte(storage.DataBlock)
+	copy(key[1:], h.BytesBE())
+	bs, err := dao.Store.Get(key)
+	if err != nil {
+		return err
+	}
+
+	b, err := block.NewBlockFromTrimmedBytes(dao.network, dao.stateRootInHeader, bs)
+	if err != nil {
+		return err
+	}
+
+	if w == nil {
+		w = io.NewBufBinWriter()
+	}
+	b.Header().EncodeBinary(w.BinWriter)
+	if w.Err != nil {
+		return w.Err
+	}
+	batch.Put(key, w.Bytes())
+
+	key[0] = byte(storage.DataTransaction)
+	for _, tx := range b.Transactions {
+		copy(key[1:], tx.Hash().BytesBE())
+		batch.Delete(key)
+		key[0] = byte(storage.STNotification)
+		batch.Delete(key)
+	}
+
+	key[0] = byte(storage.STNotification)
+	copy(key[1:], h.BytesBE())
+	batch.Delete(key)
+
+	return dao.Store.PutBatch(batch)
+}
+
 // StoreAsCurrentBlock stores a hash of the given block with prefix
 // SYSCurrentBlock. It can reuse given buffer for the purpose of value
 // serialization.