# enable_pov_reclaim.rs - source
Source of the Rust file `docs/sdk/src/guides/enable_pov_reclaim.rs`.

#
pezkuwi_sdk_docs/guides/
enable_pov_reclaim.rs

    1//! # Enable storage weight reclaiming
    2//!
    3//! This guide will teach you how to enable storage weight reclaiming for a teyrchain. The
    4//! explanations in this guide assume a project structure similar to the one detailed in
    5//! the [bizinikiwi documentation](crate::pezkuwi_sdk::bizinikiwi#anatomy-of-a-binary-crate). Full
    6//! technical details are available in the original [pull request](https://github.com/pezkuwichain/pezkuwi-sdk/issues/257).
    7//!
    8//! # What is PoV reclaim?
    9//! When a teyrchain submits a block to a relay chain like Pezkuwi or Dicle, it sends the block
    10//! itself and a storage proof. Together they form the Proof-of-Validity (PoV). The PoV allows the
    11//! relay chain to validate the teyrchain block by re-executing it. Relay chain
    12//! validators distribute this PoV among themselves over the network. This distribution is costly
    13//! and limits the size of the storage proof. The storage weight dimension of FRAME weights reflects
    14//! this cost and limits the size of the storage proof. However, the storage weight determined
    15//! during [benchmarking](crate::reference_docs::pezframe_benchmarking_weight) represents the worst
    16//! case. In reality, runtime operations often consume less space in the storage proof. PoV reclaim
    17//! offers a mechanism to reclaim the difference between the benchmarked worst-case and the real
    18//! proof-size consumption.
    19//!
    20//!
    21//! # How to enable PoV reclaim
    22//! ## 1. Add the host function to your node
    23//!
    24//! To reclaim excess storage weight, a teyrchain runtime needs the
    25//! ability to fetch the size of the storage proof from the node. The reclaim
    26//! mechanism uses the
    27//! [`storage_proof_size`](pezcumulus_primitives_proof_size_hostfunction::storage_proof_size)
    28//! host function for this purpose. For convenience, pezcumulus provides
    29//! [`TeyrchainHostFunctions`](pezcumulus_client_service::TeyrchainHostFunctions), a set of
    30//! host functions typically used by pezcumulus-based teyrchains. In the binary crate of your
    31//! teyrchain, find the instantiation of the [`WasmExecutor`](pezsc_executor::WasmExecutor) and set
    32//! the correct generic type.
    33//!
    34//! This example from the teyrchain-template shows a type definition that includes the correct
    35//! host functions.
    36#![doc = docify::embed!("../../templates/teyrchain/node/src/service.rs", wasm_executor)]
    37//!
    38//! > **Note:**
    39//! >
    40//! > If you see error `runtime requires function imports which are not present on the host:
    41//! > 'env:ext_storage_proof_size_storage_proof_size_version_1'`, it is likely
    42//! > that this step in the guide was not set up correctly.
    43//!
    44//! ## 2. Enable storage proof recording during import
    45//!
    46//! The reclaim mechanism reads the size of the currently recorded storage proof multiple times
    47//! during block authoring and block import. Proof recording during authoring is already enabled on
    48//! teyrchains. You must also ensure that storage proof recording is enabled during block import.
    49//! Find where your node builds the fundamental bizinikiwi components by calling
    50//! [`new_full_parts`](pezsc_service::new_full_parts). Replace this
    51//! with [`new_full_parts_record_import`](pezsc_service::new_full_parts_record_import) and
    52//! pass `true` as the last parameter to enable import recording.
    53#![doc = docify::embed!("../../templates/teyrchain/node/src/service.rs", component_instantiation)]
    54//!
    55//! > **Note:**
    56//! >
    57//! > If you see error `Storage root must match that calculated.` during block import, it is likely
    58//! > that this step in the guide was not
    59//! > set up correctly.
    60//!
    61//! ## 3. Add the TransactionExtension to your runtime
    62//!
    63//! In your runtime, you will find a list of TransactionExtensions.
    64//! To enable the reclaiming,
    65//! set [`StorageWeightReclaim`](pezcumulus_pezpallet_weight_reclaim::StorageWeightReclaim)
    66//! as a warpper of that list.
    67//! It is necessary that this extension wraps all the other transaction extensions in order to catch
    68//! the whole PoV size of the transactions.
    69//! The extension will check the size of the storage proof before and after an extrinsic execution.
    70//! It reclaims the difference between the calculated size and the benchmarked size.
    71#![doc = docify::embed!("../../templates/teyrchain/runtime/src/lib.rs", template_signed_extra)]
    72//!
    73//! ## Optional: Verify that reclaim works
    74//!
    75//! Start your node with the log target `runtime::storage_reclaim` set to `trace` to enable full
    76//! logging for `StorageWeightReclaim`. The following log is an example from a local testnet. To
    77//! trigger the log, execute any extrinsic on the network.
    78//!
    79//! ```ignore
    80//! ...
    81//! 2024-04-22 17:31:48.014 TRACE runtime::storage_reclaim: [ferdie] Reclaiming storage weight. benchmarked: 3593, consumed: 265 unspent: 0
    82//! ...
    83//! ```
    84//!
    85//! In the above example we see a benchmarked size of 3593 bytes, while the extrinsic only consumed
    86//! 265 bytes of proof size. This results in 3328 bytes of reclaim.
    87#![deny(rustdoc::broken_intra_doc_links)]
    88#![deny(rustdoc::private_intra_doc_links)]