Plutus: Pioneers Program 4th cohort - Lecture 4 - On-chain/Off-chain smart contract code and indexers

Cardano smart contract's code is splitted in two parts: on-chain and off-chain

On-chain code is executed during transaction/data blockchain incorporation, on blockchain's side.

• Has to be synchronized between all nodes (to ensure integrity, which is costly)
• Follows a complex compilation process:
  • PlutusTx: used by developpers (subset of Haskell/GHC)
  • GHC Core
  • Plutus Intermediate Representation (PIR)
  • Plutus Core (PLC)
  • Untyped Plutus Core (UPLC): run on the blockchain (stored in CBOR)

Off-chain code which run to build/submit transactions, on the user's side.

• Accesses wallet and resources
• Is favored (since complex on-chain will end up slowing down the whole blockchain)
• Queries the blockchain (via cardano-cli query tip|utxo|...)
  • Used for validators execution (transaction context, inputs/outputs with Values/Datums/Scripts, and our redeemer)
  • Fetch this information from
    • A Local node
    • A local database synchronized with
      • A local node
      • A remote indexer

There are many indexers:

• db-sync: PostGreSQL-based synchronization (allows to qury directly using SQL in read-only)
  • According to the documentation it also provides frontends:
    • A GraphQL API Server (Apollo)
    • A REST API Server
    • A SMASH (Stake Pool Metadata Aggregation Server) aggregating off-chain blockchain's stake pools' metadata
  • It requires a local Cardano node
• Kupo: indexes only outputs, providing a fast, high-level HTTP/JSON API
  • It is configurable such as you can only index a sub-part of all transactions
  • It can be run in-memory
  • It requires a local Cardano node
• Scrolls: Meta-indexer which relies on plugins to provide read-optimized models
  • Inputs plugins: Cardano node, Block CBOR Files
  • Outputs plugins: Redis, MongoDB, Cassandra, etc.
  • Quite early-stage at the moment
• Carp: Another PostGreSQL-based indexer (Cardano Postgres Indexer), relying on Oura
  • Provides a REST API
  • Parses raw CBOR data and stores them in PostGreSQL
  • Is highly-configurable (based on execution plans)
• Oura: Acts as tail on the transactions
  • Connects to a Cardano node
  • Outputs to Webhooks/Kafka/ElasticSeearch/stdout
  • Is configurable (filter)
• Marconi: it is supposed to be lightweight, customizable for indexing and querying Cardano
  • It requires a local Cardano node
  • Based on multiple SQLite files
  • Can index either
    • the blockchain (though marconi-chain-index), accessible via a cli
    • or sidechains (though marconi-sidechain), accessible via a HTTP JSON-RPC service

Some of the indexers are written in Rust, based on the CML library which aims to partially rewrite Cardano ecosystem.

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