From 3ea497b5a0fdda252f9c5a3c257cfaf8685f02fd Mon Sep 17 00:00:00 2001
From: asynchronous rob <rphmeier@gmail.com>
Date: Tue, 3 Oct 2023 09:23:22 -0500
Subject: [PATCH] expose the last relay chain block number as an API from
parachain-system (#1761)
re:
https://forum.polkadot.network/t/blocknumber-vs-timestamps-should-we-abandon-blocktimes-altogether/4077
This exposes the `LastRelayChainBlockNumber` storage member of
`cumulus-pallet-parachain-system` with a getter and alters the behavior
of this storage item to only be updated in `on_finalize` to ensure a
consistent value throughout `on_initialize` and within transactions.
Parachains, especially with features such as asynchronous backing and
agile coretime, should not use the parachain block number as a clock.
Any feature of Polkadot intended to optimize core utilization and
parachain coretime consumption is likely to worsen this clock as it is
practically applied.
---
cumulus/pallets/parachain-system/src/lib.rs | 23 ++++++++++++++-------
1 file changed, 16 insertions(+), 7 deletions(-)
diff --git a/cumulus/pallets/parachain-system/src/lib.rs b/cumulus/pallets/parachain-system/src/lib.rs
index a8f0a49223f..eaf15768e29 100644
--- a/cumulus/pallets/parachain-system/src/lib.rs
+++ b/cumulus/pallets/parachain-system/src/lib.rs
@@ -245,10 +245,10 @@ pub mod pallet {
<UpgradeRestrictionSignal<T>>::kill();
let relay_upgrade_go_ahead = <UpgradeGoAhead<T>>::take();
- assert!(
- <ValidationData<T>>::exists(),
- "set_validation_data inherent needs to be present in every block!"
- );
+ let vfp = <ValidationData<T>>::get()
+ .expect("set_validation_data inherent needs to be present in every block!");
+
+ LastRelayChainBlockNumber::<T>::put(vfp.relay_parent_number);
let host_config = match Self::host_configuration() {
Some(ok) => ok,
@@ -380,8 +380,7 @@ pub mod pallet {
let ancestor = Ancestor::new_unchecked(used_bandwidth, consumed_go_ahead_signal);
let watermark = HrmpWatermark::<T>::get();
- let watermark_update =
- HrmpWatermarkUpdate::new(watermark, LastRelayChainBlockNumber::<T>::get());
+ let watermark_update = HrmpWatermarkUpdate::new(watermark, vfp.relay_parent_number);
aggregated_segment
.append(&ancestor, watermark_update, &total_bandwidth_out)
@@ -460,6 +459,9 @@ pub mod pallet {
4 + hrmp_max_message_num_per_candidate as u64,
);
+ // Weight for updating the last relay chain block number in `on_finalize`.
+ weight += T::DbWeight::get().reads_writes(1, 1);
+
// Weight for adjusting the unincluded segment in `on_finalize`.
weight += T::DbWeight::get().reads_writes(6, 3);
@@ -515,7 +517,6 @@ pub mod pallet {
vfp.relay_parent_number,
LastRelayChainBlockNumber::<T>::get(),
);
- LastRelayChainBlockNumber::<T>::put(vfp.relay_parent_number);
let relay_state_proof = RelayChainStateProof::new(
T::SelfParaId::get(),
@@ -756,6 +757,8 @@ pub mod pallet {
pub(super) type DidSetValidationCode<T: Config> = StorageValue<_, bool, ValueQuery>;
/// The relay chain block number associated with the last parachain block.
+ ///
+ /// This is updated in `on_finalize`.
#[pallet::storage]
pub(super) type LastRelayChainBlockNumber<T: Config> =
StorageValue<_, RelayChainBlockNumber, ValueQuery>;
@@ -1501,6 +1504,12 @@ impl<T: Config> Pallet<T> {
Self::deposit_event(Event::UpwardMessageSent { message_hash: Some(hash) });
Ok((0, hash))
}
+
+ /// Get the relay chain block number which was used as an anchor for the last block in this
+ /// chain.
+ pub fn last_relay_block_number(&self) -> RelayChainBlockNumber {
+ LastRelayChainBlockNumber::<T>::get()
+ }
}
impl<T: Config> UpwardMessageSender for Pallet<T> {
--
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