Aparna Narayanan

Greetings all,

Zilliqa is all the time pleased to witness cases the place our know-how is in excessive use and demand. Lately, we skilled an all-time excessive on variety of sensible contract transactions on our blockchain as Unstoppable Domains went reside on July ninth, 2019 receiving overwhelming demand from the neighborhood.

Such an occasion additionally creates heavy sensible contract processing necessities on the Zilliqa mainnet. On this case, it resulted in just a few incidents of instability. This technical replace addresses these latest points, outlines the fixes applied, and upcoming technical enhancements which is able to strengthen our mainnet. In spite of everything, as we’ve all the time mentioned, fixed enrichment of the platform is essential to development and improvement.

Understanding sensible contract states

Each sensible contract has its personal state. As an example, let’s have a crowdfunding sensible contract that information every donor’s contribution. A easy sensible contract state might be represented as follows:

So long as the crowdfunding contract continues to be accepting new donors’ contributions, we will anticipate it to develop greater with time.

As you possibly can see, the sensible contract state is predicted to develop greater over time. Usually, we anticipate most sensible contracts to carry out fairly quick on Zilliqa mainnet. Nonetheless, Unstoppable Domains state measurement has elevated very quickly, leading to stalled community availability on our blockchain whereas processing these sensible contract transactions.

Within the Zilliqa blockchain, there are just a few cases when sensible contract processing is reduce off:

  1. When the gasoline restrict of a microblock is reached
  2. When the time restrict for transaction processing for a microblock is reached

On this case…

  • Because the Unstoppable Domains sensible contract state grew, we seen a linear enhance within the time wanted to course of every transaction. It was noticed that the sensible contract processing time elevated from negligible processing time to 500ms, 700ms and eventually exceeding 1s
  • As a result of heavy sensible contract processing, we hit the time restrict at every node degree, after which no transaction might be processed

A deep-dive into the incident

In a super world, if all nodes reduce off sensible contract processing precisely on the similar transaction, there wouldn’t be any points. Nonetheless, within the decentralized blockchain world, nodes do have differing machine specs. Because of this every node might course of completely different quantities of sensible contracts per microblock — and that is the place it might have an effect on the efficiency of Zilliqa mainnet.

As it’s possible you’ll know, Zilliqa makes use of PBFT for consensus. As a part of the consensus protocol (on this case for microblock), the chief first proposed a microblock with all of the sensible contract transactions processed for that microblock. The backup validates what has been proposed. In such a state of affairs, if greater than ⅓ of the backup within the community shard disagree with what the chief proposes, no consensus can be reached for that microblock.

That is what we’re at present observing.

The impression of such incidents is dependent upon the extent it happens at. If it happens on the shard degree, the microblock from that particular shard won’t be shaped for that closing block. The community will transfer on with a brand new shard chief on the subsequent Tx Epoch. If it happens on the DS committee, view change will happen to elect a brand new chief. Nonetheless, after the election of a brand new chief, an analogous concern might reoccur, leading to one other view change to re-elect one other chief.

What’s the root trigger?

There are two most important causes this occurred, as detailed beneath:

  1. Slicing off sensible contract processing needs to be dealt with first by the gasoline restrict. On this case, the gasoline restrict we set was too excessive: This setting signifies that the time restrict will all the time be hit first. It will trigger the time restrict to all the time be hit first. If the gasoline restrict was hit first, we won’t face this concern as all nodes will course of precisely the identical set of sensible contract transactions as a substitute of differing from one another, leading to no consensus attain for that microblock.
  2. Inefficient state entry: Because the state measurement for Unstoppable Domains sensible contract state grows, the processing time can be linearly elevated. This was attributable to an inefficient implementation on our Scilla interpreter’s backend. At the moment, on this explicit sensible contract, the majority of the information saved inside a map. The node might want to load in the complete map (which was rising in measurement), deserialize it and eventually replace the map. That is the principle motive why the sensible contract course of is taking extra time to course of because the sensible contract state measurement will increase.

Applied fixes and upcoming upgrades

  1. Discount of gasoline restrict constants (since model v4.7.1)

We now have considerably diminished the gasoline restrict such that it is going to be hit earlier than the time restrict for sensible contract execution. We are going to regularly enhance it again up once more after Scilla IPC and environment friendly state entry (defined beneath) is finished.

2. Automated discount of gasoline restrict after view change (can be launched in v4.8.0)

View change is a crucial part within the Zilliqa blockchain protocol. There is just one goal for view change — maintain the community alive and working. View change includes the altering of a non-performing or malicious chief to a brand new chief. This enables the protocol to renew operations after view change has occurred.

Nonetheless, on this explicit nook case, after a view change occurred, the brand new chief along with the backups did not agree on a brand new microblock. This occurred quite a few instances. Once more, that is because of the time restrict of the sensible contract processing being reached first (as defined on this blogpost).

Within the upcoming v4.8.Zero improve, we can be introducing the automated discount of gasoline restrict through exponential back-off. Merely put, this implies the gasoline restrict can be diminished by half every time the view change happens.

As an example, if there are 5 consecutive view modifications with out progress within the community, the gasoline restrict can be diminished by half every of the 5 instances. That’s 2⁵, which is 32 instances. For that exact Tx Epoch, the brand new gasoline restrict for the microblock is “the gasoline restrict divided by 32”. By exponentially lowering the gasoline restrict, the community will be capable to finally attain a consensus on the microblock because the gasoline restrict can be triggered finally. It will enable the community to progress.

After a profitable consensus, the unique gasoline restrict can be restored in order to make sure community processing functionality won’t be affected on the subsequent Tx epoch.

3. New environment friendly state entry for Scilla (slated for launch subsequent month)

This can be one of many subsequent massive updates for the Scilla sensible contract processing.

Recall that within the Unstoppable Domains sensible contract, loading in such information would require loading the JSON file, deserializing it and eventually processing it. With this new enhancement, there isn’t a must load in the complete state of the contract. Relatively, solely the report(s) that may change should be learn. It will enormously cut back the overhead of loading pointless information for sensible contract processing.

4. Scilla inter-process communication (IPC) protocol (slated for launch subsequent month)

That is one other massive replace scheduled for sensible contract processing. At the moment, to run the Scilla sensible contract, the node must invoke the Scilla interpreter binary to learn within the present states, execute the contract and output the brand new states. The method of invoking binary nevertheless, incurs some efficiency overhead. With the upcoming enhancement, we are going to transfer this strategy of invoking the binary to interprocess communication, thereby lowering pointless overhead.

To sum up, whereas we hit speed-bumps on the trail to decentralising the world, the technical group stays as dedicated as ever to delivering a sturdy and high-performance platform to assist purposes similar to Unstoppable Domains. Such points have given the technical group a very good perception into points which can floor, and we are going to proceed to make enhancements with every model we launch. Our work isn’t carried out.. Due to our wonderful group, we proceed bettering and enriching the Zilliqa blockchain, day after day.

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