Operation to modify existing limit order

[nathanielhourt]

User Story
As a market maker I (would) want an operation to modify an existing limit order so that order walls in the markets can be maintained cheaply.

Technically, this isn't for me, but @litepresence in Telegram has requested it, and it's an easy win, so I say we do it.

Impacts
Describe which portion(s) of BitShares Core may be impacted by your request. Please tick at least one box.

• API (the application programming interface)
• Build (the build process or something prior to compiled code)
• CLI (the command line wallet)
• Deployment (the deployment process after building such as Docker, Travis, etc.)
• DEX (the Decentralized EXchange, market engine, etc.)
• P2P (the peer-to-peer network for transaction/block propagation)
• Performance (system or user efficiency, etc.)
• Protocol (the blockchain logic, consensus, validation, etc.)
• Security (the security of system or user data, etc.)
• UX (the User Experience)
• Other (please add below)

Additional Context (optional)
At present, modifying a limit order on the books requires a cancel/create combo, which is a double fee. Now that the fees have risen, there is some pressure to add a limit_order_update_operation which will allow for cheaply updating limit orders.

There are two ways to modify a limit order: update the price, or update the amount. Updating the price should be extremely cheap, as this involves only a modification to one small object and re-sorting the order books. Updating the amount should cost around twice as much, as it also involves modifying the account balance.

Question: what should the fees be set to?

CORE TEAM TASK LIST

• Evaluate / Prioritize Feature Request
• Refine User Stories / Requirements
• Define Test Cases
• Design / Develop Solution
• Perform QA/Testing
• Update Documentation

[clockworkgr]

Same as cancel or half of it imho...

Still, new op so up to the committee to decide :)

[litepresence]

via telegram

litepresence, [20.02.19 18:13]
would update_op be any less bloat than cancel and create ?

Nathan Hourt, [20.02.19 18:14]
It's like 1/3
And waaayyy less processing

The whole purpose of development work on cancel order fees is to decrease chain bloat in the end. Nobody would use this feature if it cost the same as cancel because it takes more code and thought on client side to implement.

If updating is more efficient in both space and processing than we should at the very least discount it to match the decreased burden on the chain and servers. I recommend decreasing it even further to encourage its usage through subsidy by raising create and cancel; relatively inefficient means to the same end.

I would like to see:

create
cancel = 1/10 create
update = 1/10 cancel

I have made several recommendations over the past month to reduce the cost of cancel create operations from a technical standpoint:

maker/taker
minimum order size
taxing unreasonably priced orders more 
taxing high frequency in short period more than same number over longer period
merkle tree pruning of unrealized cancel operations
annual tax refund for activities technically deemed "market making" 

By comparison, limit_order_update should be 1) the easiest to implement 2) immediately tangible in results. Regardless of final fee, I think this is a great feature because it is a technical path to slow chain bloat and reduce server load other than raising taxes.

[pmconrad]

IMO 1/10 of cancel fee is too low (but that's a discussion for the committee).

Implementation should consider that after modifying the order price, order matching need only be performed if the price is adjusted in favour of the buyer AND the order stays at or moves to the front of the book. In that case, processing cost is close to limit_order_create, otherwise processing cost is extremely low.

[abitmore]

Create a BSIP please. https://github.com/bitshares/bsips/

[nathanielhourt]

Oops, didn't mean to close

[pmconrad]

I know coding is more fun, but for consensus changes we usually write a spec (aka BSIP) first. :-)

[nathanielhourt]

Wuff, so much paperwork for such a small change! No wonder nobody's done this yet... ;P OK, I'll draft it up.