Estimated proof size less than measured

Question

I was running some benchmark, and noticed that the estimated proof size was less than the measured size, despite MaxEncodedLen being used in this crate. The estimation of 0 is clearly wrong, but this is the one that gets used in Weight::from_parts. My first guess was that MaxEncodedLen was perhaps implemented incorrectly, but they're all auto-derived so I don't think that can be the case. I also tried inspecting the max_encoded_len() of of the key type, and it was non-zero. What can cause this behavior?

/// Storage: VaultRegistry MinimumCollateralVault (r:0 w:1)
/// Proof: VaultRegistry MinimumCollateralVault (max_values: None, max_size: Some(43), added: 2518, mode: MaxEncodedLen)
fn set_minimum_collateral() -> Weight {
    // Proof Size summary in bytes:
    //  Measured:  `711`
    //  Estimated: `0`
    // Minimum execution time: 9_105_000 picoseconds.
    Weight::from_parts(9_553_000, 0)
        .saturating_add(T::DbWeight::get().writes(1_u64))
}

Answer 1

Looking at the comments shows that MinimumCollateralVault was not read - therefore it should not be in the proof. The problem here is actually that the Measured is wrong. The estimated Proof size of zero is correct.

This was fixed in #13485. Please try to update your Substrate version.
In any case; thanks for letting us know, only like this can we improve! When you are sure that there is a bug, you can better open an issue in GitHub directly.