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Optimism PBC Blog

The Road to Sub-dollar Transactions, Part 2: Compression Edition

This post is the second in a series on the path to sub-dollar ORU transactions. For full context, check out the first!

Calldata Overview

Optimism uses Ethereum as a data availability layer. This means that each transaction executed on Optimism is stored (but not executed) on Ethereum. Right now we store Optimism transactions in calldata. Multiple L2 transactions are batched up into a binary blob and the blob (plus some other info) is stored in the data field of the transaction. To later retrieve that data, we look at the body of transactions (which are stored in the blocks themselves). Because Ethereum blocks are saved, the Optimism chain can always be reconstructed from Ethereum.

Compression Overview & Results

We looked at 22 thousand batches (nearly 3 million individual transactions) that Optimism had submitted to Ethereum and compressed them in different configurations to determine how to best implement compression and experiment with what is possible.

Conclusion

In summary: if historic trends continue, we can expect to reduce fees by 30–40% by introducing the compression explained above.

  • Kovan on 3/17
  • Mainnet on 3/24

Appendix: Algorithm Summary

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