Allow adjusting priority coming from Signed Extensions

[tomusdrw]

Closes #5672

The PR introduces AdjustPriority wrapper for SignedExtension. The motivation for introducing this is defined in the original issue. Basically we want to make sure that the priorities we add (coming from different Signed Extensions) are in reasonable order of magnitude.

The idea is to divide the priority of the CheckWeight so that instead of being in [0..MAX_BLOCK_WEIGHT] (for Normal transactions) range it's in [0..10] range.

The idea is to reduce the priority of the CheckWeight extension down to 0.

[kianenigma]

the code looks great, but I am still struggling to wrap my head around the 'why' of this.

Now, the priority is fee/weight ratio returned from TransactionPayment, which is some large-ish value. It seems like the range is too small to have any effect next to that, so we might as well make the priority of CheckWeight be 0. To rephrase, I am not sure where the range [0..10] comes from and why it is chosen. I presume each chain can choose their own range, but it would be good if we can give a guideline of what rationale they should use to choose the range.

[tomusdrw]

Now, the priority is fee/weight ratio returned from TransactionPayment, which is some large-ish value.

Not large enough currently on some chains. The required tip to bump priority might be unreasonably high compared to the priority coming from CheckWeight (pure weight).

To rephrase, I am not sure where the range [0..10] comes from and why it is chosen.

The range is indeed arbitrary, just to have some differentiation between transactions. We can easily scale down by MAX_BLOCK_WEIGHT + 1 to make sure that Normal transactions are always 0. However the CheckWeight priority is still necessary to make sure that Operational and Mandatory transactions are prioritised correctly. Will fix.

it would be good if we can give a guideline of what rationale they should use to choose the range.

Indeed. Basically in case the ChargeTransactionPayment extension is added the original priority for Normal transactions coming from CheckWeight can be easily turned off (i.e. scaled down to 0), since the former takes into account all: weigh&tlength (fee) and the tip.

[kianenigma]

LGTM, but needs a companion to apply sensible values to polkadot runtimes as well.

[tomusdrw]

@kianenigma added the companion: paritytech/polkadot#3743

[JoshOrndorff]

Looks good to me. We're excited to get this one on Moonriver.

[tomusdrw]

Closing in favour of #9834