runtime/session-info: use `Executive` for migration

This issue has been created since 2022-01-13.

@kianenigma brought this to my attention:

We're using a deprecated mechanism for runtime migration in session-info:

impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
fn on_runtime_upgrade() -> Weight {

instead, we should do something like
It would be good to write some pre/post-conditions as well, e.g. ensuring the length of Sessions is preserved.

This is also true for the Configuration pallet.

bkchr wrote this answer on 2022-01-13

While @kianenigma is right, for concrete blockchain implementations I don't see such a huge need for putting everything into the runtime file. The point being here is that this stuff isn't reused by others and they are not getting fucked that easily. For migrations in Polkadot it is completly okay to remove them after they are applied on chain, because they will never be required anymore.

ordian wrote this answer on 2022-01-14

I guess the main benefit is being able to test with try-runtime and writing down the migration invariants explicitly.

bkchr wrote this answer on 2022-01-14

Try runtime also works on pallet level.

kianenigma wrote this answer on 2022-01-14

Yes try-runtime works for both.

While Basti's argument is correct, I think it will still make life easier for everyone if we stick to doing migrations via the top level runtime only. At the minimum, it makes it a few clicks easier to track which migration went into which release.

That being said, i don't think this needs an issue. If this is already release/deployed, then too late. Else, we can only change it until the next release, so better make a PR directly rather than an issue that could get lost :p

ordian wrote this answer on 2022-01-14

If this is already release/deployed, then too late

I believe it will be released in 0.9.16, which is not cut yet.
I opened this issue as a good-first-issue for new joiners.

ECJ222 wrote this answer on 2022-01-17

Can I take on this issue?

ordian wrote this answer on 2022-01-17

Can I take on this issue?

please do!

ECJ222 wrote this answer on 2022-01-26

Hi @ordian,

Please could you write a short description of this issue?

ordian wrote this answer on 2022-01-27

I'm going to close the issue, because we already branched off for the next release and it doesn't make sense to change it in the version after next because the migration will not run anymore.

More Details About Repo
Owner Name paritytech
Repo Name polkadot
Full Name paritytech/polkadot
Language Rust
Created Date 2018-08-09
Updated Date 2022-09-27
Star Count 6266
Watcher Count 479
Fork Count 1387
Issue Count 590


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