Currently the yield produced from lending markets Compound/Aave is collected upon each deposit into SAVE. This is an expensive operation and is performed more frequently than is necessary. This proposal provides a more passive method of collecting the yield, reducing SAVE deposit gas costs by >= 50% while delivering a smoother result.
This upgrade is something that could be bundled nicely to mip-3
There are 2 primary sources of income from mAsset - SWAP fees, and Lending market income. This MIP will make 2 fundamental changes to the way system income is collected and distributed. The first of which is how the SWAP fees are tracked over time, and the second of which is the frequency of lending market interest is collected. The lending market interest will be collected intermittently and streamed second by second to SAVE.
On deposit, currently there are a number of interactions involved in collecting system interest before it is credited
to SAVE to the benefit of the existing savers. The flow goes something like
BasketManager > eachBasset[
Example of a deposit transaction: tenderly.co/tx/main/0xf73…
Current gas cost: ~390,739
The part of the transaction, from
BasketManager onwards, is proposed to be omitted. In this function,
for each basset a
IPlatformIntegration(integrations[i]).checkBalance(b.addr); call is made - this is expensive due to the way
Aave and Compound check balances for underlying assets.
Potential savings: ~210k or ~54%
If we were to continue without this change, the gas costs would increase by ~30k for each bAsset added in to the system.
This MIP will solve the problem by making the following changes:
1 - Change the way SWAP fees are recorded in
Currently the SWAP fees are implicitly recorded as deltas in each bAssets
vaultBalance property by subtracting
the full amount (including fee) during a SWAP. When the interest is collected in
BasketManager, the gain is
delta = balance.sub(oldVaultBalance);. Instead of recording fees implicitly like this, we will instead
track fees natively in the
Masset.sol at the cost of an extra SSTORE to each SWAP/REDEEM.
2 - Change the default behaviour of the
collectInterest function in
Simply remove the call
basketManager.collectInterest(); and mint mAsset to the amount of fees that have been collected.
3 - Change the method of lending market interest collection & distribution (
As opposed to collecting lending market interest each deposit, we will add a new function to
Masset.sol that specifically collects
the interest from the lending markets and deposits it to the SavingsManager. Following the mechanism in mip-2 in which
a publicly accessible function is called intermittently, we will then stream the collected yield over the course of a DAY to SAVE.
The ideal solution:
- a) Lowers gas costs for SAVE deposit
- b) Does not present unfair opportunities for participants to time SAVE deposits and “steal” yield
- c) Does not increase gas costs substantially (1 SSTORE is fine) for mint/swap/redeem
The above properties were taken into account and used as benchmarks on the following decisions:
1 - SWAP fee collection: immediate vs streamed
The SWAP fee collection could have been bundled in with the lending market collections and made once per day. While this would offer significant gas advantages, it would give market participants the opportunity to time their SAVE deposits with high SWAP volumes, and thus steal yield from loyal participants (b).
2 - Lending market fee collection: immediate vs streamed
The lending market yield could simply be immediately distributed to SAVE (during the next SWAP fee collection cycle) but this would provide unfair advantages for participants who could time their deposits correctly (b).
3 - SWAP fee tracking
Given the active proposal in MIP-3 which sees gas costs vastly reduced across the board, spending an extra 5k to
update a global param is not much of a problem. Instead of setting the variable to
0, we will set it to
1, thus causing
5k for both swap/redeem, as well as 5k for SAVE. This is a compromise for both user groups.
Tracks the units of fees that have been accrued since last collection (in mAsset terms)
Turns accrued SWAP fees into mAsset and sends to SavingsManager
Collects the lending market interest and sends to the SavingsManager to
be streamed over the course of a day
Deposits the lending market yield and streams over the course of a day, bundling with existing stream.
Configurable Values (Via MCCP)
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