Coin Days Destroyed used as part of priority - exploring the utility as a basis for further decisions

I’ve created this topic in order to spin the CDD discussion out from the ‘Lower the default relay fee’ thread and into its own thread so we can get a clearer picture of

  • who is employing it in their software right now?
  • what are the benefits?

Those points at the very least are worth documenting as part of the ongoing discussions.

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Thanks @freetrader for creating the topic. I’m a little confused about the first bullet point though.

Hmm. Nobody. It has been disabled in BTC since 2016, and in BCH since BCH existed. BCH has never used this mechanism (it did exist, but disabled, in the codebase at one point but was never used, AFAIK). It definitely does not exist now.

EDIT: Oh I see what you mean. Yeah I do think Flowee at least has some code still in their codebase for this (perhaps?). But even so “resurrecting” the old core code (or designing new similar logic) is not a difficult task… the logic is pretty easily implemented.

As for the second bullet-point:

It’s an “easy” alternative to modifying the existing 1 sat/B fee default. We just don’t touch the default (or we may, but that is orthogonal to this).

Just enabling CDD prioritization again is a way for BCH to offer 0-fee or very-low-fee tx capability to wallets wishing to take advantage of it. If we enabled CDD as a way to add “fee-like” priority to txs, then we could say “BCH has free txs!” as a marketing / public perception thing.

This should also mitigate the worry that if BCH does really moon to $20k or $50k per coin at some point – everybody could still transact (provided they were using aged coins to do so). Nobody would be priced out.

This, unlike simply lowering the fee – comes with “built-in” flood protection. Whatever the price may do (including crash!), we can forever offer extremely low-cost and/or free txs on BCH without the transaction-flood-worry being an issue (since it’s impossible to flood coindays coins without significant “locking” of funds for a significant amount of time).

In summary: Unlike lowering fee**, which carries the flood risk in the event of catastrophic price crash – CDD guarantees flooding is forever not an issue while at the same time making free (or very low fee) txns possible immediately (once rolled-out).

** - Note that one can do CDD and also lower fee at the same time. It’s not either/or. They are just 2 alternatives that can be done together or separately.


The main benefit is that flooding mempools is no longer just a question of dollars per day. Flooding becomes something that takes expertise, patience and locking up real amounts of funds for considrerable amount of time.

The same point much more obviously stated: when there is some sort of mempool flooding attempt they will have no effect on actual economic users. Normal payments from normal people will for the VAST majority of cases end up being coins that are relatively old. They stand out as “good” transactions.

  • Another benefit I can think of is that it can be used to give increased relaying priority to “older coins” which would hamper potential spam/DoS attacks even further.

Also thanks @tom and @cculianu for reminding me all the most important reasons why Coin Days Destroyed were an awesome feature. I knew they were awesome, but after 5+ years I have already forgotten why.