Introduction

Not being able to persist data across calls would limit the utility of smart contracts. Think of these problems:

• How could a smart contract implement a token if it could not keep track of balances?
• How could a smart contract implement a voting system if it could not keep track of votes?
• How could a smart contract implement a game if it could not keep track of scores?

This is why a CosmWasm smart contract has access to the storage facilities offered by the Cosmos SDK (opens in a new tab). These facilities are essentially a binary key-value store, with records stored on-chain.

Storage limits

While developing smart contracts, it's important to remember on-chain storage is, as always, pricey. Conventionally, developers often draw the line at a "small logo image" (think a few KBs). If you need to store bigger things, it's likely time to consider off-chain storage (like IPFS or some centralized storage). Techniques for securely and reliably storing large data off-chain are beyond the scope of this document.

Trying to minimize bloat is always good practice when it comes to on-chain storage.

What cw-storage-plus builds on

The smart contract framework itself (cosmwasm-std) provides a simple API for storing and retrieving data. If you're curious, you can check it out right here (opens in a new tab).

This API is raw in that it exposes the binary key-value store. While you're free to use it directly, you're likely to find that finicky and error-prone. cw-storage-plus is a library that builds on top of this API to do the following:

• eliminate the need to manually serialize and deserialize data
• provide a type-safe interface for storing and retrieving data
• help manage keys
• provide featureful persistent data structures

Let's explore!