What are "Blob-carrying transactions"? How do they reduce Layer 2 costs?

好的，没问题！咱们用大白话聊聊这个话题。

Blob Transactions: Equipping Layer 2 Networks with a "Data Cheat Code" for Massively Reduced Costs

Hello! I see you're interested in "Blob-carrying transactions." This is truly the core of Ethereum's Dencun Upgrade, and it's the key to significantly lowering transaction fees on various Layer 2 networks (such as Arbitrum, Optimism, zkSync, etc.).

Below, I'll try to explain it to you in an easy-to-understand way.

What are "Blob-carrying transactions"?

Simply put, Blob transactions are a brand-new data "delivery" service on Ethereum, specifically designed for Layer 2 networks.

You can imagine it like this:

Before Blob transactions, all Layer 2 networks (which we'll call L2s), to ensure their security, needed to regularly package a large amount of transaction data and "post" it to the Ethereum mainnet (Layer 1) for public verification. This was like the L2 saying: "Hey, everyone on the mainnet, I just processed these transactions; all the data is here, so you can check anytime if I've done anything wrong."

However, the old method of "posting" this data package was clunky and very expensive. L2s used a place called calldata to store data, a space shared by all types of transactions. It's like this:

Before: If an L2 wanted to post a public announcement (publish data), it had to go to the busiest commercial street downtown and rent an advertising space as expensive as a luxury store (using calldata). Not only was it costly, but it also had to bid against everyone else who wanted to advertise (regular transfers, DeFi operations, etc.).

The advent of Blob transactions, however, completely changed the game. It's as if Ethereum officially opened up a huge, temporary "community bulletin board" right next to the commercial street. This bulletin board is what we call a Blob.

This "community bulletin board" (Blob) has several key features:

Massive Space: A single Blob can hold approximately 128KB of data, significantly more than the previous method.
Super Cheap: It has its own independent "rent" calculation method (a separate fee market), so it doesn't compete for space with the commercial street's ad slots (regular transactions), making the price extremely low.
Temporary Storage: The information posted on the bulletin board (Blob data) is only retained for about 18 days. After this period, it's purged because L2s only need to ensure data availability during this time; once the "traceability period" passes, there's no need for permanent storage.
Read-Only: Smart contracts on the mainnet cannot directly read or manipulate the data within a Blob. Its sole purpose is to "be seen," serving as proof that the L2 is not falsifying data.

Therefore, a "Blob-carrying transaction" is a transaction that includes a pointer to a specific area on this "community bulletin board." The transaction itself is small, but it "carries" a large, inexpensive data package (Blob).