Once again my attempt to summerize and explain the weekly bitcoin developer meeting in layman's terms.
*Disclaimer*
Please bear in mind I'm not a developer and I'd have problems coding "hello world!", so some things might be incorrect or plain wrong.
Like any other write-up it likely contains personal biases, although I try to stay as neutral as I can.
There are no decisions being made in these meetings, so if I say "everyone agrees" this means everyone present in the meeting, that's not consensus, but since a fair amount of devs are present it's a good representation.
The dev IRC and mailinglist are for bitcoin development purposes. If you have not contributed actual code to a bitcoin-implementation, this is probably not the place you want to reach out to. There are many places to discuss things that the developers read, including this sub-reddit.
Main topics discussed where:
Mempool limiting
sendheaders BIP
versionbits
dev/discuss list policy
CHECKSEQUENCEVERIFY
**Mempool limiting**
- background
When a transaction is relayed across the network it is held by the nodes in memory, until it gets into a block. All these transactions that sit in memory are called the memorypool or mempool for short.
Like we could see during the spam-attack if there's a big back-log of transactions that couldn't make it in the blockchain this mempool can get pretty big resulting in nodes crashing.
To stop this from happening devs are trying to find a way to limit this mempool, so a mechanism to reject and/or remove transactions from the mempool. The hard part here is to make it so nodes can't be attacked by abusing this mechanism.
- meeting comments
While testing, sipa encountered transactions that took 200ms to be accepted into the mempool.
As it's the first time he has benchmarked this and the pull-request shouldn't make an impact on these times it likely doesn't have anything to do with this. However, such times are bad either way.
Question on why we should revert the minrelay (minimum fee for nodes to relay a transaction) back to 1000 (it has been set to 5000 to quick-fix the mempool issues), sipa thinks it should be floating as well or the dust limit becomes ineffective.
- meeting conclusion
**sendheaders BIP**
- background
Copy/paste from the BIP:
Since the introduction of "headers-first" downloading of blocks in 0.10, blocks will not be processed unless they are able to connect to a (valid) headers chain. Consequently, block relay generally works as follows:
1. A node (N) announces the new tip with an "inv" message, containing the block hash
2. A peer (P) responds to the "inv" with a "getheaders" message (to request headers up to the new tip) and a "getdata" message for the new tip itself
3. N responds with a "headers" message (with the header for the new block along with any preceding headers unknown to P) and a "block" message containing the new block
However, in the case where a new block is being announced that builds on the tip, it would be generally more efficient if the node N just announced the block header for the new block, rather than just the block hash, and saved the peer from generating and transmitting the getheaders message (and the required block locator).
- meeting comments
Question on how to move forward. How to let the nodes know you want the blockheader instead of the blockhash.
Options:
Extend the version message.
Have an "options" message that can send flags.
Send a "sendheaders" message early when connecting so the way peers want their block announcement is immediately known.
Send a "sendheaders" message at any time, changing the way peers want their block announcement from hashes to headers.
No one likes to extend the version message further.
There's no strong advantage to have an "options" message over a "sendheaders" message.
Having the message being sent early on might be too constraining. Possible usecase from morcos: "its entirely possible some future optimization may say, i want to send sendheaders to these peers b/c they announce a lot of new stuff to me and not these others b/c they don't".
Most people like this to be enable-only, so no message to get back to receiving blockhashes. Which is how the BIP was drafted.
-meeting conclusion
sdaftuar does a pull-request for the BIP to get a number assigned and proceeds with the BIP as drafted.
**versionbits**
- background
Currently softforks have been done by the isSuperMajority mechanism, meaning when 95% of the last X blocks has a version number higher than Y the fork is deployed.
A new way of doing this is currently being worked on and that uses all bits of the version number, appropriately being called versionbits. So instead of a fork happening when the version is larger than (for example) 00000000011 (3), a fork happens when (for example) the 3rd bit is up (so 00100000011).
This way softforks can be deployed simultaneous and independant of each other.
- meeting comments
copy/paste from IRC, since I don't know what this specifically means:
CodeShark: so right now it's just a unit that implements the versionbits logic but does not demonstrate its usage
I thought it would be better to actually integrate in a separate PR, but I can add a demonstration
sipa: separate commit, same PR - i think we need something that's mergable as a whole, to be able to see whether the whole thing easily backports
Codeshark (who's implementing versionbits) had some more remarks but no one present had seemed to reviewed it, so not much use in discussing things further.
- meeting conclusion
**dev/discuss list policy**
- background
The bitcoin-dev mailing list is intented for technical discussions only. There's things that don't belong there but need to be discussed anyway.
Now this is done in bitcoin-dev, but the volume of this is getting too big.
For the things that don't belong on bitcoin-dev, but need to be discussed anyway there's a new list being created namely bitcoin-discuss as well as clear policies and moderation for both.
- meeting comments
Bitcoin-discuss was created, but the admin password wasn't distributed to jgarzik who's willing to guide the moderatation.
Separate moderation-proposals have been done meanwhile.
People just want it to move on.
- meeting conclusion
Since none of the people who proposed a moderation-scheme are present we'll let them discuss it among each other and post their decisions publicly.
**CHECKSEQUENCEVERIFY**
- background
CheckLockTimeVerify (CLTV) repurposes the nSequence field (nSequence are 4 bytes intended for sequencing time-locked transactions, but this never got used). However, there's no way use these values in a bitcoin script.
CheckSequenceVerify (CSV) makes this field accessible to bitcoin scripts.
- meeting comments
CLTV is pretty much done.
Check to see maaku moving one of the bits to allow for other implementations to have better granularity has any objections.
As long as we're using as few bits as possible the exact semantics are less important for most people.
CSV is not on target for the end of of the month, although a lot of work and progress has been made.
- meeting conclusion
**Participants**
wumpus Wladimir J. van der Laan
sipa Pieter Wuille
btcdrak btcdrak
gmaxwell Gregory Maxwell
morcos Alex Morcos
maaku Mark Friedenbach
CodeShark Eric Lombrozo
BlueMatt Matt Corallo
sdaftuar Suhas Daftuar
warren Warren Togami
GreenIsMyPepper Joseph Poon
davec Dave Collins
cfields Cory Fields
jonasschnelli Jonas Schnelli