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FeePoolState

Description

This contract composes persistent state storage for the issuance percentage and index for each address interacting with the fee pool. These details are stored for the last six fee periods.

As a persistent state contract, FeePoolState is not intended to be easily upgraded, as opposed to the FeePool itself, which is so intended.

See FeePool.feesByPeriod and FeePool.effectiveDebtRatioForPeriod for discussion of the meaning of this information held in this contract and how it is used.

Caution: The Number of Stored Fee Periods

Note that this contract contains storage for up to six fee periods, while the FeePool contract limits it to only three. This is a consequence of the implementation of SIP 4, which reduced the fee window in the main FeePool contract in order to encourage faster responses to alterations of system incentives. As part of this process, this storage contract was, of course, not upgraded.

See also: Design_Decisions.md.

Source: FeePoolState.sol

Architecture


Inheritance Graph

FeePoolState inheritance graph

No Relation To The State Contract

Although this contract is called FeePoolState, be aware that it does not inherit from the State contract.



Libraries


Structs


IssuanceData

Holds the issuance state and index of users interacting with the FeePool for the last several fee periods.

Fields

Field Type Description
debtPercentage uint The percentage of the total system debt owned by the address associated with this entry at the time of issuance. These are 27-decimal fixed point numbers, closely related to the values in SynthetixState.debtLedger.
debtEntryIndex uint The debt ledger index when this user issued or destroyed tokens. That is, the length of the ledger at the time of issuance.

For more information on these fields and their meaning, see the main Oikos contract functions _addToDebtRegister and _removeFromDebtRegister, along with the corresponding struct in SynthetixState.

Relationship with SynthetixState

This is the same struct as SynthetixState.issuanceData, modulo naming, but in the case of SynthetixState, only one entry is kept, corresponding to only the most recent issuance event associated with an address.

This induces a slightly awkward structure where the current and historical issuance information is stored over two separate contracts. In a future version this information could potentially be stored in a unified structure for dividends in efficiency and clarity.


Variables


FEE_PERIOD_LENGTH

The number of fee periods (6) worth of issuance data to keep. Note the inconsistency with the corresponding constant in FeePool, which is set to 3.

Type: uint8 constant public

Value: 6


feePool

The address of the main FeePool contract.

Type: address public


accountIssuanceLedger

A list of up to 6 issuance data entries for each address, for the most recent changes to their issuance level. The fee periods do not have to be consecutive, but they are ordered from newest to oldest (decreasing debt ledger indexes).

Note that the entry accountIssuanceLedger[account][0] only corresponds to the current fee period if appendAccountIssuanceRecord(account, *, *, *) has been called during the current fee period. That is, if the account has issued or burnt synths this period.

Type: mapping(address => IssuanceData[FEE_PERIOD_LENGTH]) public


Functions


constructor

Initialises the fee pool address, as well as the inherited SelfDestructible and LimitedSetup instances. The setup period is initialised to six weeks.

Details

Signature

constructor(address _owner, FeePool _feepool) public

Superconstructors


setFeePool

Changes the fee pool address.

Details

Signature

setFeePool(FeePool _feePool) external

Modifiers


getAccountsDebtEntry

Accesses accountIssuanceLedger.

The first return value is a 27-decimal fixed point number.

Details

Signature

getAccountsDebtEntry(address account, uint index) public view returns (uint debtPercentage, uint debtEntryIndex)

Preconditions


applicableIssuanceData

From a given account's issuance data, retrieve the most recent entry which closed before the provided index. If there is no such entry, (0,0) is returned.

This function is used in FeePool.feesByPeriod and FeePool.effectiveDebtRatioForPeriod to compute the fees owed to a user for specific past periods.

The returned values are as per getAccountsDebtEntry, hence the first return value is a 27-decimal fixed point number.

Details

Signature

applicableIssuanceData(address account, uint closingDebtIndex) external view returns (uint, uint)


appendAccountIssuanceRecord

Allows the Oikos contract, through FeePool.appendAccountIssuanceRecord, to record current fee period issuance information for a given account in the issuance ledger. This is used when synths are issued or burnt.

If the latest entry in this account's issuance ledger was from the current fee period, it is overwritten. Otherwise, the existing entries are shifted down one spot, dropping the last one (using a call to issuanceDataIndexOrder), and a new entry is added at the head of the list.

The debtRatio argument is a 27-decimal fixed point number.

Details

Signature

appendAccountIssuanceRecord(address account, uint debtRatio, uint debtEntryIndex, uint currentPeriodStartDebtIndex) external

Modifiers


issuanceDataIndexOrder

Shifts this account's array of issuance ledger entries down one place, overwriting the last entry. This is only used in appendAccountIssuanceRecord.

Details

Signature

issuanceDataIndexOrder(address account) private


importIssuerData

This function was used during the initial six week setup period to initialise the issuance ledger from the previous Oikos version.

Details

Signature

importIssuerData(address[] accounts, uint[] ratios, uint periodToInsert, uint feePeriodCloseIndex) external

Modifiers

Preconditions

  • The transaction reverts if the length of accounts and ratios differ.

Emits


Modifiers


onlyFeePool

Reverts the transaction if msg.sender is not the fee pool address.


Events


IssuanceDebtRatioEntry

Record that an entry was updated in the issuance ledger by the importIssuerData function during the setup period.

Signature: IssuanceDebtRatioEntry(address indexed account, uint debtRatio, uint feePeriodCloseIndex)