Pool Coin Decimal Truncation During Deposit

[dongsam]

Summary of Bug

• when the unit size of the pool coin is significantly large
• when user deposits relatively small amount of coin into the liquidity pool

Version

Including v1.4.0, past versions.

Steps to Reproduce

Example

• pool created with unit coin value $10
• user deposits $19 amount of liquidity into the created pool
• user's share should be 1.9 unit pool coin, but because of decimal truncation, user gets only 1 unit pool coin
• user lost $9 amount of deposited coin because 1 unit pool coin value is only $10

Why It Happened?

• reason why some of the pool unit coins have significantly large USD value?
  • because some of the pools were created with a large initial deposit
    • first depositor always get 1,000,000 pool unit coin
    • if the initial deposit is larger than $1M, then the pool unit coin will be larger than $1
• we expected this risk when we designed the spec
• but we couldn't forecast that actually, some users create pools with +$1M initial deposit

The pools that have these problems.

• CRO · ATOM
  • https://app.emeris.com/pool/9
• IRIS · ATOM
  • https://app.emeris.com/pool/8
• REGEN · ATOM
  • https://app.emeris.com/pool/6
• Sentinel · ATOM
  • https://app.emeris.com/pool/7
• AKT · ATOM
  • https://app.emeris.com/pool/5

Solution

Refund of Decimal Part of the Deposit

• we can calculate "maximum integer unit pool coin receivable" for each deposit request
• the module receives the exact number of deposit coins with respect to the calculated number of unit pool coins, and the rest are refunded
• with the refund feature, users are free from decimal truncation loss from receivable pool coin when they deposit liquidity

Patch Plan

• we will steadily prepare this patch, accompanied with enough testing and simulation
• if we can make time before Cosmos-SDK 0.44 upgrade, we will propose this into the upgrade
• if we cannot make it, then this refund feature will be proposed to the next Gaia upgrade schedule

Param change

• Apart from Patch, we plan to submit a parameter change proposal to increase the params.InitPoolCoinMintAmount to minimize this problem even if some users create pools with +$1M initial deposit in the future.

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For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned