bsips/bsip-0018.md

BSIP: 0018
Title: Revive BitAsset through buying Settlement Pool
Authors: Fabian Schuh, Peter Conrad
Status: Installed
Type: Protocol
Created: 2017-06-05
Discussion: https://bitsharestalk.org/index.php/topic,24322.0.html
Worker: 1.14.56

Abstract

BitAssets, i. e. market-pegged assets (MPA) like bitUSD in BitShares can suffer a "global settlement" event. After global settlement, the asset is effectively rendered useless. This BSIP proposes a protocol change to enable resolving a global settlement so that affected assets can be continued and put to good use again.

Motivation

The necessity of reviving bitassets has already been discussed in BSIP-0017, and is unquestioned.

Market-pegged assets, aka SmartCoins are among the core features of the BitShares blockchain and as such provide one of our unique selling points.

MPAs can suffer a "global settlement" event. A global settlement occurs when the least collateralized short position has insufficient collateral to buy back the borrowed SmartCoins at the current feed price. What happens then is that the MPA is tagged with a "settlement price", defined as the collateral ratio of the least collateralized short. All short positions are closed automatically, by collecting sufficient collateral into a settlement pool and paying out the remainder to the short's owners. MPA holders can use the forced settlement operation to receive their share from the settlement pool in exchange for their MPAs. Even after global settlement, market-pegged assets can still be transferred or traded, but they can no longer be borrowed.

Currently, in BitShares, there is no actual way to resolve the global settlement, but eventually, all significant holders will have to settle their positions to obtain BTS for their long position. Some dust will remain scattered all over the place, where the value of the dust position is lower than the fees required to get rid of it.

Rationale

When a market-pegged asset undergoes a global settlement, one of the crucial mechanisms that support the peg (namely "margin calls") is no longer available. However, other mechanisms, such as the "face-value", trading and settlement still exist and, unless the valuation of the underlying asset decreases significantly, the outstanding debt (the BitAsset long positions) are still collateralized through the settlement pool at the fixed settlement price. It is even possible that the value of the collateral exceeds the nominal value of the MPA significantly.

For example, if a global settlement event happened on USD at a price of 1 bitUSD/BTS, then an outstanding debt of 1000 bitUSD would be backed by 1000 BTS in the settlement pool of the bitUSD asset. No other call positions would be open by anyone else. Every bitUSD long position could, in this case, claim BTS from the settlement pool at a rate of 1:1.

Proposal

All that is needed for the asset to be revived is:

• re-enable price feeds
• replace the settlement pool with sufficiently collateralized call positions.

Since after a global settlement, the collateral for the outstanding long positions are stored in the settlement pool, we here propose a way to obtain the funds in the settlement pool and its outstanding debt from the network. Since the collateral ratio of the settlement pool after a global settlement is 100%, obtaining the settlement funds in order to convert it into an open call position requires to also provide additional collateral or reduce the debt in order to not cause another global settlement or margin call right away.

Specifications

Like in BSIP-0017, let SWAN be an asset that has seen global settlement, and let BACK be the asset backing SWAN.

Bugfix: MPAs that have seen a global settlement cannot be settled after the price feed expires

It has turned out that force-settling an MPA requires a valid price feed even when the MPA has a settlement_price set. This is clearly a bug, since in that case the settlement price is independent from the price feed. Furthermore, publishing price feeds is no longer possible after a global settlement, so the time when settlement is possible at all is limited to the expiration period of the price feed of the MPA.

This bug will be fixed. See https://github.com/cryptonomex/graphene/issues/664#issuecomment-254056746 for a discussion.

(This fix is also part of BSIP-0017. Obviously, it needs to be fixed only once. It is repeated here because it is currently unclear which of these proposals will be implemented.)

Auto-revive after increase of settlement fund value

This applies only to SmartCoins, not to Prediction Markets.

A price increase of BACK can lead to the situation where SWAN is worth much more than it was originally intended to be. I. e. the value of the settlement fund becomes much greater than the nominal value of the existing supply of SWAN.

When the value of the settlement fund reaches the minimum required collateral (in terms of price feed and MCR), a call_order_object owned by the issuer of SWAN is created (or updated) that takes the settlement_fund as collateral and covers the full debt. The settlement_fund and the settlement_price will then be cleared, which revives the asset.

The condition can easily be checked at the time the price feed is updated. Obviously, this requires a price feed. Currently it is not possible to publish a price feed for assets that have seen global settlement. This restriction will be removed.

Recollateralize

This applies only to SmartCoins, not to Prediction Markets.

Overview

The idea of turning the settlement fund into a short position when its value has increased sufficiently can easily be extended. If the value of the settlement fund itself is too low to create a sufficiently collateralized short position (in terms of price feed and MCR), investors could volunteer to add the required amount of collateral to the fund and take ownership of the resulting short position (collateral+debt).

The proposed operation enables potential investors to "bid" additional collateral for taking over part of the debt (or all of it). When enough bids have been made to cover the full outstanding debt, and all of them are sufficiently collateralized (in terms of price feed and MCR), the settlement_fund and the bids are turned into call positions. Finally, the settlement_price is removed from the asset, which revives it.

If the available bids cover more than the outstanding debt, bids with a higher collateral/debt ratio are preferred over those with a lower ratio. The intent is to turn the competition among investors into better collateralized calls, which is in the interest of the MPA holders.

bid_collateral_operation

The operation has the following payload:

• fee(asset_type): The operation requires a fee to be paid
• bidder(account_type): This account pays the additional collateral and will become the owner of the resulting call position, if the bid is accepted
• additional_collateral(asset_type): Collateral paid by the account in order to support the call position
• debt_covered(asset_type): The amount of debt the account is willing to cover

The operation works as follows:

1. It pays a fee
2. If account has already placed a bid on the same MPA, the existing bid is cancelled (see below).
3. If debt_covered equals 0, no further action is taken.
4. It reduces the account's balance by additional_collateral.
5. It creates a collateral_bid_object containing the bidder and the partial inverted swan price calculated as additional_collateral / debt_covered.

The required validity checks for the operation are:

• debt == 0 || debt > 0 && collateral > 0

The required evalutation checks for the operation are:

• debt_covered.asset must be a bitasset (not a PM) with a settlement_price
• additional_collateral.asset must be the asset backing SWAN
• account must have sufficient BACK, i. e. at least additional_collateral

Obviously, the operation must be authorized by bidder.

collateral_bid_object

The collateral_bid_object stores information about bids offered by accounts using the bid_collateral_operation. It is indexed

1. by_id
2. by debt asset and bidder
3. by debt asset and partial inverted swan price.

When a collateral_bid_object is cancelled, the additional_collateral (i. e. the partial inverted swan price's base) is returned to the bidder and the collateral_bid_object is deleted.

The intent of the partial inverted swan price is to facilitate selection of the bids that will result in the call_order_objects with the lowest debt/collateral ratio after the revival of the bitasset.

Maintenance

In every maintenance interval, all MPAs that have a settlement_price are checked if

• they have a valid price feed, and
• if enough sufficiently collateralized bids are available to cover the debt.

If both conditions are met, for each collateral_bid_object (in order of descending partial inverted swan price) a new call_order_object will be constructed in this way, starting with remaining_debt=SWAN.current_supply:

• call.borrower = bid.bidder
• call.debt = bid.debt.amount
• call.collateral = call.debt * SWAN.settlement_price + bid.additional_collateral.amount
• remaining_debt -= call.debt
• SWAN.settlement_fund -= call.debt * SWAN.settlement_price

If remaining_debt reaches 0, any remaining bids will be cancelled. It is likely that for the last converted bid the requested debt will be less than the remaining_debt. In that case, call.debt will be set to remaining_debt and call.collateral will be set to asset.settlement_fund + additional_collateral.

execute_bid_operation

In order to make the revival event visible in the bid owners' account histories, a new virtual execute_bid_operation will be introduced, that contains these parameters:

• the bidder
• the actual covered debt
• the total collateral of the resulting call_order

The semantics of that operation includes the removal of the existing bid and the creation of the new call_order as described above.

Discussion

Partially Obtaining Settlement Funds

In the case a widely used BitAsset is globally settled, the cost of providing sufficient collateral and the associated risk may be prohibitively high. The proposed bidding mechanism allows to split the cost (and the risk) among multiple participants.

BitAssets using BitAssets as collateral are unaffected

One huge advantage of this approach over BSIP-0017 is that BitAssets which are collateralized by other BitAssets are not directly affected by this proposal. Even though the economical debt of such asset may be argued about if the collateral asset experienced a global settlement, the technical debt is unaffected. Converting the settlement pool into a regular call position through this proposal would not only restore the original BitAsset, but also reset the collateral of the derived BitAsset.

Cost vs. Profit

This operation opens an interesting cost vs. profit trade-off for those willing to take the risk of using this operation that we would like to discuss. Keep in mind that

• the valuation of the collateral may be volatile (e.g. in case of BTS)
• after global settlement, the long positions can settle and thus reduce the debt as well as the settlement pool

Market participants that are willing to take risk may want to obtain a larger chunk of a settlement pool as it means an instant short position.

Feeds

Re-collateralization is deliberately not restricted to the issuer of the globally settled bitasset. The intent here is to incentivize potential investors. Effectively, during an uptrend in the value of the collateral, this works like a reverse auction. A higher value of the collateral results in a lower required amount for re-collateralization, i. e. the chance/risk ratio increases. This incentive makes sense, because additional collateral is in the best interest of the holders of the settled BitAsset.

This "reverse auction" ends when the BitAsset is auto-revived by creating a short position for the issuer. At that point, an "investor" could re-collateralize with zero risk, which is no longer in the interest of the holders.

Summary for Shareholders

This proposal presents a flexible way of reviving a BitAsset that has experienced a global settlement event. The blockchain or shareholders do not need to take any risk as the proposal only offers a new way for market participants to (partially) revive the BitAsset.

Copyright

This document is placed in the public domain.