Stable storage not working as expected

Developers
,
1

I’m in the progress of moving all our data to stable storage, but it seems that its not so stable. When i push upgrades the data gets wiped. I’m not sure what is causing this behaviour but i will explain the setup below;

We have an index canister that manages the upgrades of the children (which migrated to stable storage).

What we do to upgrade a child canister;

  • The child WASM in included into the index canister WASM
  • There are some checks done to see if its actually a new child WASM to prevent unnecessary upgrades
  • The child canister upgrades are triggered on the post_upgrade step by;
set_timer(Duration::from_secs(0), || {
    ic_cdk::spawn(ScalableData::upgrade_children());
});

which eventually goes loops over all child canister and call

canister.install_code(
    InstallCodeMode::Upgrade,
    data.child_wasm_data.bytes.clone(),
    (),
).await;

i run a script to generate the WASMs, and gzip them

#!/bin/sh

canisters=(
    "child"
    "parent"
)

echo -e "${GREEN}> $ENV: Generating required files..${NC}"
cargo test --test generate
dfx generate --network ic

for t in ${canisters[@]}; do
    echo -e "${GREEN} $ENV > Building $t..${NC}"
    dfx build --network ic $t

    mkdir -p wasm
    cp -r target/wasm32-unknown-unknown/release/$t.wasm wasm/$t.wasm
    gzip -c wasm/$t.wasm > wasm/$t.wasm.gz

    mkdir -p frontend/$t
    cp -a src/declarations/$t frontend
done

rm -rf src/declarations
echo -e "${GREEN} $ENV > Stopping local replica..${NC}"

Once that is done i run;

dfx canister install parent --network ic --wasm wasm/parent.wasm.gz --mode upgrade

For the child canisters i’ve setup the stable storage like this;

type Memory = VirtualMemory<DefaultMemoryImpl>;

thread_local! {
    pub static MEMORY_MANAGER: RefCell<MemoryManager<DefaultMemoryImpl>> =
        RefCell::new(MemoryManager::init(DefaultMemoryImpl::default()));


        // STABLE
        pub static STABLE_DATA: RefCell<StableCell<Data, Memory>> = RefCell::new(
            StableCell::init(
                MEMORY_MANAGER.with(|m| m.borrow().get(MemoryId::new(0))),
                Data::default(),
            ).expect("failed")
        );

        pub static ENTRIES: RefCell<StableBTreeMap<String, Member, Memory>> = RefCell::new(
            StableBTreeMap::init(
                MEMORY_MANAGER.with(|m| m.borrow().get(MemoryId::new(4))),
            )
        );

    // OLD NON STABLE
    pub static DATA: RefCell<ic_scalable_misc::models::original_data::Data<Member>>  = RefCell::new(ic_scalable_misc::models::original_data::Data::default());
}

Where we also still use the pre- post upgrades in case stable storage doesn’t work as expected so we have a backup

#[pre_upgrade]
pub fn pre_upgrade() {
    DATA.with(|data| ic_methods::deprecated_pre_upgrade(data))
}

#[post_upgrade]
pub fn post_upgrade() {
    DATA.with(|data| ic_methods::deprecated_post_upgrade(data))
}

So after upgrading the child canister through the index, all data is wiped, am i doing something wrong or is this a bug?

I’m using ic-stable-structures = "0.6.0"

1 Like
2

Can you share how deprecated_pre_upgrade is implemented? My first guess is that deprecated_pre_upgrade is overwriting the stable storage in a way that corrupts the stable structures.

I recommend looking at the quickstart example, which shows how you can have stable structures and heap data coexisting - take a special look at the pre/post upgrade hooks there and how the data on the heap is being written to stable memory.

1 Like
3

The deprecated methods look like this, i’m using ic_cdk v0.11.0

pub fn deprecated_pre_upgrade<T: Serialize + CandidType + DeserializeOwned>(
    data: &RefCell<ic_scalable_misc::models::original_data::Data<T>>,
) {
    storage::stable_save((&*data.borrow(),)).unwrap();
}

pub fn deprecated_post_upgrade<T: Serialize + CandidType + DeserializeOwned>(
    data: &RefCell<ic_scalable_misc::models::original_data::Data<T>>,
) {
    let (old_store,): (ic_scalable_misc::models::original_data::Data<T>,) =
        storage::stable_restore().unwrap();
    *data.borrow_mut() = old_store;
}

and i did check that out, i had an other post about that here Migrate non-stable storage to stable storage on single canister

Do need to say that at that time the focus was to keep non-stable persistent so i wouldn’t loose it through upgrades.

But i will check it out again, see if i can spot something

4

@RMCS That’s exactly the problem. You’re using stable_save and stable_restore for data on the heap, while you’re using the MemoryManager for stable structures. Unfortunately, stable_save and stable_restore end up clobbering the MemoryManager since it overwrites it.

The MemoryManager must be the only way you write to stable memory to keep everything safe. In this case, you should serialize/deserialize the state on your heap into one of the memories of the MemoryManager. The quickstart example I linked to above shows how to do that. See the upgrade hooks in that example.

3 Likes
5

I forgot to respond after confirming that the issue was resolved by checking out the post- pre upgrade from the example you provided.

I blindly assumed that the old method would still work, also I was afraid of touching the existing pre- post upgrade code and loose the data if i did it wrong.

But all is resolved, thank for the help!