Separates the debt snapshot logic out of Issuer, and into a new DebtCache contract.
This SIP proposes adding a new DebtCache contract, along with a RealtimeDebtCache implementation\ninheriting DebtCache, which will be used on L2 where debt snapshots are not required.\nAll debt cache related functions that currently exist in Issuer will be moved into the new contracts.
The modifications applied in SIP-83 to cache the total system debt increased the size of the Issuer\ncontract to the point that its compiled bytecode was too large to be deployed on the L2 OVM. As the L2\ndeployment of Synthetix has no execution costs, debt snapshots are unnecessary in this context.\nBy separating out the snapshot logic, the Issuer and DebtCache contracts will individually fit into the\ncontract size limit on L2, and the DebtCache itself can be individually replaced with a RealtimeDebtCache\nversion which does not require cache synchronisation.
This structure will also allow debt cache logic to be upgraded without modifying the Issuer, which when\nredeployed requires a time-consuming process of re-adding all Synths to the system.
Although in principle one could simply replace the entire Issuer contract with a different version for L2,\nthis would require modifying the internal structure of that contract, and entail multiple versions of the\ncore debt snapshot code to exist. This would increase the overhead of making contract modifications in the\nfuture. By separating out the logic into a new contract, this overhead is reduced, and the Issuer contract's\nsize is brought down much further below the fundamental size limits imposed by the OVM, allowing more headroom\nto extend its functionality.
Many functions will be renamed in this refactor; although in many cases no functionality will change, these\nmodifications to the interface are in service of making it clearer, more consistent, and more complete.
\nIssuer will no longer be responsible for maintaining the debt cache, but will instead pass this responsibility on to\nthe new DebtCache contract.
The following functions, and a number of supporting internal functions will be moved from the Issuer and into a\nnew contract called DebtCache. These functions will be renamed to clarify the resulting interface. Several new functions\nwill added to round out its functionality and simplify the implementation.
Issuer Function | \nDebtCache Function | \nDescription | \n
|---|---|---|
debtSnapshotStaleTime | \ndebtSnapshotStaleTime | \nReports the current snapshot stale time. | \n
currentSNXIssuedDebtForCurrencies | \ncurrentSynthDebts | \nReports the debt values for a set of synths at current prices and supply. | \n
cachedSNXIssuedDebtForCurrencies | \ncachedSynthDebts | \nReports the cached debt values for a set of synths. | \n
currentSNXIssuedDebt | \ncurrentDebt | \nReports the current total system debt value across all synths. | \n
cachedSNXIssuedDebtInfo | \ncacheInfo | \nReports the cached system debt, when a snapshot was last taken, and the cache's invalidity and stale status | \n
cacheSNXIssuedDebt | \ntakeDebtSnapshot | \nTakes completely fresh debt snapshot, updating the cache, timestamp, and validity status. | \n
updateSNXIssuedDebtForCurrencies | \nupdateCachedSynthDebts | \nModifies the cached debt value with the deltas from a specific set of synths. | \n
purgeDebtCacheForSynth | \npurgeCachedSynthDebt | \nAdmin function to purge the cached value of a specific Synth if it was not added/removed from the system properly after an upgrade. | \n
updateSNXIssuedDebtForSynth | \nupdateCachedSynthDebtWithRate | \nAllows the issuer and exchanger contracts to update a synth's cached debt without refetching its price | \n
updateSNXIssuedDebtOnExchange | \nDeleted | \nExchange-specific logic will be moved into the Exchanger contract; the same functionality will be implemented with the new updateCachedSynthDebtsWithRates function. | \n
| None | \nupdateCachedSynthDebtsWithRates | \nAs updateCachedSynthDebtWithRate, but for a set of synths. | \n
| None | \nupdateDebtCacheValidity | \nAllows the issuer to invalidate teh cache when adding or removing synths. | \n
| None | \ncachedDebt | \nReports the cached system debt. | \n
| None | \ncacheTimestamp | \nThe timestamp that the cache was last refreshed with a full snapshot. | \n
| None | \ncacheInvalid | \nTrue if the cache has been invalidated by, or since, the last full snapshot. | \n
| None | \ncacheStale | \nTrue if the cache timestamp is older than the stale time. | \n
The DebtCacheSynchronised event will be renamed to DebtCacheSnapshotTaken.
In addition, the issuer itself will also gain a new function, Issuer.synthAddresses(bytes32[] memory currencyKeys) returns (ISynth[] memory),\nwhich will be used by the debt cache to obtain several synth addresses in a single function call in order to fetch the\ntotal supply of each.
To simplify implementation, offset the gas cost of the additional function call, the cached debt values will be stored in\nthe debt cache contract itself rather than in flexible storage.\nThere is less of a necessity to persist this information since it no longer rides along with the issuer, but in addition\nstoring the cache in the contract will decrease gas consumption for any account calling\ntakeDebtSnapshot, which will improve gas costs for the snapshot keeper, which must run regularly to keep the\ndebt snapshot from going stale.
On L2 DebtCache will be replaced by RealtimeDebtCache, which is a drop-in replacement that shares an identical\ninterface; but its semantics will be altered as follows:
cacheInfo will report realtime values from currentDebt for the debt and invalidity. The cache timestamp will always report as the current block timestamp, and the cache will never be stale.cachedSynthDebts will report realtime values from currentSynthDebts.takeDebtSnapshot will become no-ops.While the Issuer is being modified, functions to add and remove multiple Synths at once will also be added,\nwhich will speed up redeployments of the Issuer (among other operations) by batching Synth migrations rather\nthan performing them one by one.
Test cases are included with the implementation in its pull request.
\nCopyright and related rights waived via CC0.
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