Runtime Upgrade: Transaction exhaust block limits

Question

I usually use scheduler to upgrade my runtime and it was working fine until now.

I have Transaction exhaust block limits trying to upgrade live chain. I build the wasm using srtool v0.9.19, and the compact wasm size is around 4.3Mb. Then, I checked out my previous release commit and the wasm build at that commit is about 3.1Mb, so maybe the size difference is the problem?

I also use sudo.sudoUncheckedWeight but the transaction is stuck at broadcast status on the Polkadot UI.

Parameters:

• Block Limits: 5Mb
• Block Weights: 1 seconds, since we're using 3 seconds block time

Please, any suggestion would be very helpful.

Answer 1

The issue is resolved by using .compact.compressed.wasm produced by srtool. I believe using plain cargo build should also produce the .compact.compressed.wasm.

Thanks for the support

Answer 2

You could

1. turn on lto to reduce the size of the wasm blob.

In Cargo.toml, add lto = true in the [profile.release] section:

[profile.release]
lto = true

This gives LLVM many more opportunities to inline and prune functions. Not only will it make the .wasm smaller, but it will also make it faster at runtime! The downside is that compilation will take longer.

2. tell LLVM to optimize for size instead of speed.

LLVM's optimization passes are tuned to improve speed, not size, by default. We can change the goal to code size by modifying the [profile.release] section in Cargo.toml to this:

[profile.release]
opt-level = 's'

Or, to even more aggressively optimize for size, at further potential speed costs:

[profile.release]
opt-level = 'z'

Note that, surprisingly enough, opt-level = "s" can sometimes result in smaller binaries than opt-level = "z". Always measure!

3. Use the wasm-opt tool.

The Binaryen toolkit is a collection of WebAssembly-specific compiler tools. It goes much further than LLVM's WebAssembly backend does, and using its wasm-opt tool to post-process a .wasm binary generated by LLVM can often get another 15-20% savings on code size. It will often produce runtime speed ups at the same time!

# Optimize for size.

wasm-opt -Os -o output.wasm input.wasm

# Optimize aggressively for size.
wasm-opt -Oz -o output.wasm input.wasm

# Optimize for speed.
wasm-opt -O -o output.wasm input.wasm

# Optimize aggressively for speed.
wasm-opt -O3 -o output.wasm input.wasm

From my experience wasm-opt is able to reduce a node_runtime.compact.wasm from 4.3MB to 3.8 MB. Your mileage may vary.

$ du -sh ./target/release/wbuild/node-runtime/node_runtime.compact.wasm
4.3M    ./target/release/wbuild/node-runtime/node_runtime.compact.wasm
$ wasm-opt -Oz -o output.wasm ./target/release/wbuild/node-runtime/node_runtime.compact.wasm
$ du -sh output.wasm 
3.8M    output.wasm

References:

• https://rustwasm.github.io/docs/book/reference/code-size.html#shrinking-wasm-code-size

Edit: Sorry for lack of details on my first post attempt. I've added all the steps for you to follow and hope it works for you too.