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Schedule an Upgrade

Now that the Node Template has been upgraded to include the Scheduler pallet, the schedule function can be used to perform the next runtime upgrade. In the previous section, the sudo_unchecked_weight function was used to override the weight associated with the set_code function; in this section, the runtime upgrade will be scheduled so that it can be processed as the only extrinsic in a block.

Prepare an Upgraded Runtime

This upgrade is more straightforward than the previous one and only requires updating a single value in runtime/src/lib.rs aside from the runtime's spec_version.

pub const VERSION: RuntimeVersion = RuntimeVersion {
  spec_name: create_runtime_str!("node-template"),
  impl_name: create_runtime_str!("node-template"),
  authoring_version: 1,
  spec_version: 102,  // *Increment* this value.
  impl_version: 1,
  apis: RUNTIME_API_VERSIONS,
  transaction_version: 1,
};

/*** snip ***/

parameter_types! {
  pub const ExistentialDeposit: u128 = 1000;  // Update this value.
  pub const MaxLocks: u32 = 50;
}

/*** snip ***/

This change increases the value of the Balances pallet's ExistentialDeposit - the minimum balance needed to keep an account alive from the point-of-view of the Balances pallet.

Keep in mind that this change will not cause all accounts with balances between 500 and 1000 to be reaped - that would require a storage migration, which is out of scope for this tutorial.

Build the Upgraded Runtime

cargo build --release -p node-template-runtime

This will override any privous build artifacts! So if you want to have a copy on hand of your last runtime Wasm build files, be sure to copy them somewhere else.

Upgrade the Runtime

In the previous section, the Scheduler pallet was configured with the Root origin as its ScheduleOrigin, which means that the sudo function (not sudo_unchecked_weight) can be used to invoke the schedule function. To upgrade the runtime:

  • Use this link to open the Polkadot JS Apps UI's Sudo tab. Refresh your browser if you have it already running to make sure that the Extrinsics for the Scheduler pallet show.
  • Wait until all the other fields have been filled in before providing the when parameter.
  • Leave the maybe_periodic parameter empty and the priority parameter at its default value of 0.
  • Select the System pallet's set_code function as the call parameter and provide the Wasm binary as before.
  • Leave the "with weight override" option deactivated.

Once all the other fields have been filled in, use a block number about 10 blocks (1 minute) in the future to fill in the when parameter and quickly submit the transaction.

Scheduled Upgrade Panel

You can use the template node's command line output or the Polkadot JS Apps UI block explorer to watch as this scheuled call takes place.

Scheduled Success Runtime Upgrade Version 102

After the target block has been included in the chain, the version number in the upper-left-hand corner of Polkadot JS Apps UI should reflect that the runtime version is now 102.

You can then observe the specific changes that were made in the upgrade by using the Polkadot JS Apps UI Chain State app to query the existentialDeposit constant value from the Balances pallet. (You may again need to refresh the page)