[FR] - Faster verification of on-disk cache

[Fjodor42]

Internal/External
External

Area
Other

Describe the feature you'd like
Drastic reduction of time needed for verification of on-disk blockchain state

Describe alternatives you've considered

1. Parallelisation if the CPU-bound parts of the verification process
2. Checksum-based checkpoints to skip through full verification of the full on-disk blockchain copy

Additional context / screenshots
For quite some time, using Daedalus, that Electron client will frequently revert back to the semblance of the start-up screen, with the point "Verifying on-disk blockchain state" showing 99.something percent, "Replaying ledger from on-disk blockchain" showing a low percentage, and "Syncing blockchain" showing 0.00%.

Remedy is restart of cardano-node.

This will, of course, trigger a verification of the on-disk blockchain state, which, on my system, pegs a single CPU core to 100%, but only reads from disk in "bursts" of between ~5MB/s to ~35MB/s, and the process takes several hours to complete.

Since a single core is utilised to 100%, and disk read speeds are low, it must be possible to parallelise parts of whatever it does, and it should also be possible to avoid actually reading the whole shebang on each (re-) start.

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[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 120 days.

[ch1bo]

Maybe this could be resolved by allowing cardano-node to use all / more cores through the Haskell RTS options?

I heard somewhere that the node uses by default only two cores.

[Fjodor42]

Thank you, @ch1bo!

For me, specifically, I don't think I am using Docker, so would it be possible for me to just specify -N (or other options) somewhere in a config file?

Again, specifically for me, Cardano-node seems to actually be started by Daedalus Wallet on Linux.

[Fjodor42]

Update from my end: Having seen what I reported with cardano-node via Daedalus, actually getting cardano-node to pick up +RTS -N -RTS (I have since settled for +RTS -N8 +RTS) turned out to be rather involved, probably mainly due to my unfamiliarity with the system (NixOS) they rely on for making a single distributable package, so I shall spare you the details.

The relevant part for this thread is that not only does that speed up things considerably, but it also seems to work around another problem I had with cardano-node seemingly losing connection to mainnet, necessitating a process restart. Whether that is a function of this being run by Daedalus, however, is unknown to me.

Hence, I shall take my findings up with the Daedalus developers, and leave it up to to the cardano-node developers to decide upon whether to implement one or more of my suggestions - for them, it would probably still be relevant, though, to promote RTS options somehow.