Add BSIP 33

bsip-0033.md

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+    BSIP: 0033
+    Title: Maker Orders With Better Prices Take Precedence
+    Author: Abit More <https://github.com/abitmore>
+    Status: Draft
+    Type: Protocol
+    Created: 2018-02-17
+    Discussion: https://github.com/bitshares/bitshares-core/issues/625
+    Replaces: -
+    Worker: To be done
+
+# Abstract
+
+Currently, when matching taker limit orders with maker limit orders, the maker
+limit orders with better prices will always be matched first.
+
+For example, if trader A has a limit order selling 100 BTS at
+0.1 USD per BTS, trader B has a limit order selling 100 BTS at 0.09 USD per BTS,
+which means B's limit order has a better price for the opposite side to buy.
+Now if trader C placed an order that buys 10 BTS at 0.105 USD per BTS, B's
+limit order will take precedence, A's limit order won't be matched.
+
+However, when there are margin call orders in the market which have met the
+requirements that to be matched, they always take precedence over limit orders
+on the same side, no matter whether the limit orders provided better price.
+
+For example, if trader A's margin call order is selling 100 BTS at no less than
+0.1 USD per BTS, trader B has a limit order selling 100 BTS at 0.09 USD per BTS,
+which means B's limit order has a better price for the opposite side to buy.
+Now if trader C placed an order that buys 10 BTS at 0.105 USD per BTS, A's
+margin call order will take precedence, B's limit order won't be matched. That
+means C is forced to "buy high" when have chance to "buy low".
+
+This BSIP proposes a mechanism to change this behavior to: always match taker
+orders with maker orders with better prices first.
+
+# Motivation
+
+Make the exchange system more user-friendly.
+
+# Rational
+
+To attract more users, the system should be fair.
+
+It's common sense that, in a continuous trading market, new orders should be
+matched with the orders on the opposite side which offerred best prices first.
+
+# Specifications
+
+There is a parameter in price feed named MSSR, which stands for "maximum short
+squeeze ratio". Maker price of margin call orders is MSSP, which stands for
+"maximum short squeeze price", is calculated as `feed_price / ( 100% + MSSR )`.
+Note: `feed_price` here is in terms of debt/collateral, aka "how much debt per
+collateral".
+
+New limit order is being processed in `apply_order(...)` function of `database`
+class.
+
+Currently, in the function, firstly call orders will be checked and matched.
+After that, limit orders on the opposite side will be checked and matched.
+
+Need to change the logic to:
+* match the new limit order with limit orders on the opposite side whose price
+  is below MSSP first,
+* if the new order is still there, match it with call orders,
+* if the new order is still there, match it with rest limit orders.
+
+# Discussion
+
+[to be added if any]
+
+# Summary for Shareholders
+
+[to be added if any]
+
+# Copyright
+
+This document is placed in the public domain.
+
+# See Also
+
+* https://github.com/bitshares/bitshares-core/issues/625
+* https://bitsharestalk.org/index.php?topic=25926.0