Backup and other feature requests

[Elmit2015]

I feel increasingly uncomfortable if there is:

• no reliable backup
• parallel channels or both side funded channels
• channel top up payments

Maybe we can setup a voting system to get features ranked by importance, like the video voting of Rene.

I know there are hundreds of things to do.

[Coinomatron]

As a test, I'm mirroring the .lightning/ folder via a bash script:

while true; do inotifywait -r -e modify,create,delete /home/user/.lightning/; rsync -avz /home/user/.lightning/ /home/user/LN_folder_backup/; done

Seems to work, just restarted the client using the backup dir and made a payment. Maybe someone else can verify if this is a sufficient method for backing up.

[rustyrussell]

The Right Way is to have a plugin with hooks at the db level, so you back up before c-lightning continues. That plugin could back up anywhere. I'm looking at it now, for 0.7.1; agreed it's vital!

[manreo]

Do that and I'm switching from lnd to c-lightning :)

[ZmnSCPxj]

The Right Way is to have a plugin with hooks at the db level

Does this mean the plugin needs an implementation of SQLite3?

What exactly are the db-level hooks we want? Do we ask SQLite to provide a correctly-escaped query for every db query we make, then pass that sanitized query to the hook before invoking SQLite on the sanitized query?

[trueptolemy]

What exactly are the db-level hooks we want?

I think it's db_write hook #2421 , and it passes database changes to hook.
I also think about the plugin to backup, and aslo not sure if plugin should implemente a SQLite directly.
It seems indeed need.

[trueptolemy]

Does this mean the plugin needs an implementation of SQLite3?

Another idea is:
Based the database, we can extract the channel event and implement the compatibility with SCB for Lnd.

[ZmnSCPxj]

Based the database, we can extract the channel event and implement the compatibility with SCB for Lnd.

If I understand correctly, recovering an SCB in lnd simply marks the channel such that on next reconnect to the peer, lnd falsely accuses it of not following the protocol, causing the peer to unilaterally close in despair.

If the peer suspects your node is lnd, and that you were using an SCB, it could replay old state and the lnd node will not be able to revoke it.

The only safe backup in Poon-Dryja is replicating the database.

I would argue that a proper replicating self-healing filesystem would be more reliable than anything we could build on top of this mechanism, if only because well tested replicating self-healing filesystems already exist.

[trueptolemy]

@ZmnSCPxj Thank you for your explanation. I learned a lot from it!