core: lessen mem-spike during 1.8->1.9 conversion (#19610)

* core/blockchain: lessen mem-spike during 1.8->1.9 conversion

* core/blockchain.go: make levedb->freezer conversion gradually

* core/blockchain: write the batch

core/blockchain.go

@@ -927,6 +927,12 @@ func (bc *BlockChain) truncateAncient(head uint64) error {
 	return nil
 }
 
+// numberHash is just a container for a number and a hash, to represent a block
+type numberHash struct {
+	number uint64
+	hash   common.Hash
+}
+
 // InsertReceiptChain attempts to complete an already existing header chain with
 // transaction and receipt data.
 func (bc *BlockChain) InsertReceiptChain(blockChain types.Blocks, receiptChain []types.Receipts, ancientLimit uint64) (int, error) {
@@ -998,7 +1004,7 @@ func (bc *BlockChain) InsertReceiptChain(blockChain types.Blocks, receiptChain [
 				}
 			}
 		}()
-		var deleted types.Blocks
+		var deleted []*numberHash
 		for i, block := range blockChain {
 			// Short circuit insertion if shutting down or processing failed
 			if atomic.LoadInt32(&bc.procInterrupt) == 1 {
@@ -1033,12 +1039,40 @@ func (bc *BlockChain) InsertReceiptChain(blockChain types.Blocks, receiptChain [
 
 				// Always keep genesis block in active database.
 				if b.NumberU64() != 0 {
-					deleted = append(deleted, b)
+					deleted = append(deleted, &numberHash{b.NumberU64(), b.Hash()})
 				}
 				if time.Since(logged) > 8*time.Second {
 					log.Info("Migrating ancient blocks", "count", count, "elapsed", common.PrettyDuration(time.Since(start)))
 					logged = time.Now()
 				}
+				// Don't collect too much in-memory, write it out every 100K blocks
+				if len(deleted) > 100000 {
+
+					// Sync the ancient store explicitly to ensure all data has been flushed to disk.
+					if err := bc.db.Sync(); err != nil {
+						return 0, err
+					}
+					// Wipe out canonical block data.
+					for _, nh := range deleted {
+						rawdb.DeleteBlockWithoutNumber(batch, nh.hash, nh.number)
+						rawdb.DeleteCanonicalHash(batch, nh.number)
+					}
+					if err := batch.Write(); err != nil {
+						return 0, err
+					}
+					batch.Reset()
+					// Wipe out side chain too.
+					for _, nh := range deleted {
+						for _, hash := range rawdb.ReadAllHashes(bc.db, nh.number) {
+							rawdb.DeleteBlock(batch, hash, nh.number)
+						}
+					}
+					if err := batch.Write(); err != nil {
+						return 0, err
+					}
+					batch.Reset()
+					deleted = deleted[0:]
+				}
 			}
 			if count > 0 {
 				log.Info("Migrated ancient blocks", "count", count, "elapsed", common.PrettyDuration(time.Since(start)))
@@ -1066,7 +1100,11 @@ func (bc *BlockChain) InsertReceiptChain(blockChain types.Blocks, receiptChain [
 		previous = nil // disable rollback explicitly
 
 		// Wipe out canonical block data.
-		for _, block := range append(deleted, blockChain...) {
+		for _, nh := range deleted {
+			rawdb.DeleteBlockWithoutNumber(batch, nh.hash, nh.number)
+			rawdb.DeleteCanonicalHash(batch, nh.number)
+		}
+		for _, block := range blockChain {
 			// Always keep genesis block in active database.
 			if block.NumberU64() != 0 {
 				rawdb.DeleteBlockWithoutNumber(batch, block.Hash(), block.NumberU64())
@@ -1079,7 +1117,12 @@ func (bc *BlockChain) InsertReceiptChain(blockChain types.Blocks, receiptChain [
 		batch.Reset()
 
 		// Wipe out side chain too.
-		for _, block := range append(deleted, blockChain...) {
+		for _, nh := range deleted {
+			for _, hash := range rawdb.ReadAllHashes(bc.db, nh.number) {
+				rawdb.DeleteBlock(batch, hash, nh.number)
+			}
+		}
+		for _, block := range blockChain {
 			// Always keep genesis block in active database.
 			if block.NumberU64() != 0 {
 				for _, hash := range rawdb.ReadAllHashes(bc.db, block.NumberU64()) {