Extrinsics

(a.k.a. Types of Transactions)

Pallets and Extrinsics

Polkadot is built using Substrate, a modular framework to efficiently build blockchains. Substrate's FRAME development environment provides modules called pallets and support libraries that you can use, modify, and extend to build the runtime logic to suit the needs of your blockchain. You can explore Substrate's FRAME pallets on this dedicated page.

Within each functional pallet on the blockchain, one can call its functions and execute them successfully, provided they have the permission to do so. Because these calls originate outside of the blockchain runtime, such transactions are referred to as extrinsics. Extrinsics normally contain a signature, some data to describe if the extrinsic has passed some validity checks and a reference to the pallet and call that it is intended for. For example, the Staking pallet contains all functions related to staking. A nominator can bond funds and nominate validators by issuing the respective extrinsics. Some extrinsics might also trigger an event on the chain such as a reward payout to the nominators.

Types of Extrinsics

Now that we introduced the term extrinsic, let us dive deeper and understand what extrinsics really are. Extrinsics can be one of 3 distinct types:

• Signed transactions: these must contain the signature of the account sending the inbound request to the runtime. With signed transactions, the account used to submit the request typically pays the transaction fee and must sign it using the account's private key.
• Unsigned transactions: these don't carry any information about who submitted the transaction, since the format of this type of transaction doesn't require a signature. You can define what conditions must be met for such a transaction to be valid.
• Inherents: are a special type of unsigned transaction made by block authors which carry information required to build a block such as timestamps, storage proofs and uncle blocks.

Here are some key differences between the different types of extrinsics:

• Contrary to signed transactions, unsigned transaction types require implementing custom validation logic which can consume more resources for checking validity compared to signed transactions.
• Unsigned transactions have no economic deterrent to prevent spam or replay attacks, so custom logic must account for protecting the network from these types of transactions being misused.
• Inherents exist to address the need of adding some data to a block, whereas signed or unsigned transactions exist to potentially change the state of the blockchain.

Metadata Updates

Before signing extrinsics with the Polkadot{.js} wallet or Cere Explorer, always check for metadata updates.

Parity Signer vs Browser Extension

Parity Signer updates the full metadata through the QR fountain while the extension updates the metadata index (the metadata is not loaded into it). As a consequence the process of updating metadata is different in this two cases (you will notice that on the Signer app the update takes longer for example). Having outdated metadata on the Signer app will prevent you from signing, while on the extension you will be able to click the sign button but the extrinsic will likely fail (similarly of having an outdated Ledger app). In general, failing to update metadata will most likely result in you not being able to sign extrinsics.

Verifying Extrinsics

Do not sign a transaction if you can't verify what you are signing or you suspect you might be signing a different extrinsic than the one intended.