Neo Column

In Neo2, the method of synchronize block is extra sophisticated. There are two steps: synchronize block headers and synchronize blocks.

As proven within the following determine, is the movement chart of synchronization mechanism of Neo2. Synchronize block headers corresponds to 1,2 steps:

1. When the native node finds that the native blockchain peak is decrease than the peak of the distant node, it’ll ship a GetHeanders (header hash) message, the place the header hash is the hash similar to the block head with the very best peak of native node.

2. After the distant node receives the request, it’ll return the desired variety of Headers from the corresponding header within the header hash to the native node (the default most variety of Headers requests is 2000).

After the block headers are synchronized, the blocks shall be synchronized. This course of corresponds to the steps within the determine 3–7:

3. After the block headers are synchronized, the hash similar to the native block with the very best peak shall be discovered.

4. Ship the GetBlock(hash) message to the distant node primarily based on the hash discovered.

5. When the distant node receives the request, it will get the hash similar to the beginning block and the variety of blocks requested (the default most quantity is 500). Then, ranging from this hash, the corresponding hash values of the desired variety of blocks are obtained in flip, and all of the hashes are put into one hash[]. When the fetch is full, the hash[] is returned to the native node as an Inv message.

6. When the native node receives the Inv message, it filters the hash[] within the Inv message and places the filtered hash[] into the Getdata request and sends it to the distant node.

7. The distant node receives a GetData(hash[]) request, will get the corresponding block for every hash within the hash[], and sends the blocks to the native node.

It may be seen that the block synchronization mechanism of Neo2 is comparatively complicated, with the next issues:

1. The sample of synchronizing the block headers first after which the blocks has vital benefits in blockchains that will fork, as a result of the headers synchronization could be very quick and might rapidly choose longer chain. However the consensus algorithm utilized by NEO determines that its blockchain won’t be forked. So the benefits of header-first mode have change into out of date. If we now not use this sample, we will save the community overhead of block headers synchronization.

2. The present GetBlocks command is inefficient and the identify is deceptive. By identify, we’ll obtain the blocks, however in actual fact, we’ll obtain an Inv message containing a hash array. The hash array within the Inv message is then filtered, and the corresponding blocks are obtained utilizing the GetData(hash[]) command.

In keeping with some issues in block synchronization mechanism of Neo2, we improved the block synchronization mechanism in Neo3 as follows:

1. The block headers synchronization mechanism was eliminated and the block peak was used to synchronize the blocks instantly as a substitute.

2. Add GetBlockData(IndexStart,rely) message, you possibly can instantly get the desired blocks from IndexStart, no must get by means of Inv message, cut back the community communication overhead.

3. Added SyncManager to handle block synchronization duties.

As proven within the following determine, is the movement chart of the block synchronization mechanism of Neo3.

It’s primarily divided into the next steps:

1. First, the blockchain peak is synchronized with the distant node by way of the PingPong message.

2. If the native blockchain peak is decrease than the distant node peak, a GetBlockData message is shipped to get the lacking blocks.

3. The distant node sends the request blocks in flip to the native node.

4. SyncManger data the acquired block indexs.

5. Ship the acquired block to the native node.

6. The native node validates the validity of the block. If it’s a legitimate block, a Persevered Block Index is shipped to the SyncManager, and the block synchronization course of ends.

7. Whether it is an invalid block, ship an Invalid Block Index to SyncManager, and SyncManager will reselect different nodes to assign the duty. And mark the node that despatched the invalid block.

For the synchronization mechanism of Neo2 and Neo3, we examined the block synchronization velocity underneath totally different circumstances as follows:

P2P Sync time(seconds) with StatesDumper intalled (begin from index 0)
Enhance about 7 instances.

P2P Sync time(seconds) with out StatesDumper intalled (begin from index 30)
Enhance about 4~5times.

Conclusion: The brand new block synchronization mechanism successfully reduces the community communication overhead and drastically improves the velocity of P2P block synchronization. It additionally lays the inspiration for node well being.

Notice: The code associated to the above scheme remains to be underneath evaluate and doesn’t essentially signify the ultimate design scheme.

By Xiaoyun Yang

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