# Stable storage not working as expected

**URL:** <https://forum.dfinity.org/t/stable-storage-not-working-as-expected/23822>\
**Category:** Developers\
**Tags:** rust, stable-memory\
**Created:** [October 17, 2023, 9:28am UTC](https://forum.dfinity.org/t/stable-storage-not-working-as-expected/23822 "2023-10-17T09:28:52Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![rem.codes](https://sea1.discourse-cdn.com/flex023/user_avatar/forum.dfinity.org/rem.codes/32/40260_2.png) [@rem.codes](https://forum.dfinity.org/u/rem.codes)\
**Post date:** [October 17, 2023, 9:28am UTC](https://forum.dfinity.org/t/stable-storage-not-working-as-expected/23822/1 "2023-10-17T09:28:53Z")

</div>

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;

```rs
set_timer(Duration::from_secs(0), || {
    ic_cdk::spawn(ScalableData::upgrade_children());
});

```

which eventually goes loops over all child canister and call

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

```

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

```bash
#!/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;

```auto
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;

```rs
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

```rs
#[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"`

---

<div class="post-metadata">

**Author:** ![ielashi](https://sea1.discourse-cdn.com/flex023/user_avatar/forum.dfinity.org/ielashi/32/15704_2.png) [@ielashi](https://forum.dfinity.org/u/ielashi)\
**Post date:** [October 17, 2023, 11:03am UTC](https://forum.dfinity.org/t/stable-storage-not-working-as-expected/23822/2 "2023-10-17T11:03:01Z")

</div>

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](https://github.com/dfinity/stable-structures/blob/main/examples/src/quick_start/), 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.

---

<div class="post-metadata">

**Author:** ![rem.codes](https://sea1.discourse-cdn.com/flex023/user_avatar/forum.dfinity.org/rem.codes/32/40260_2.png) [@rem.codes](https://forum.dfinity.org/u/rem.codes)\
**Post date:** [October 17, 2023, 11:08am UTC](https://forum.dfinity.org/t/stable-storage-not-working-as-expected/23822/3 "2023-10-17T11:08:16Z")

</div>

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

```rs
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](https://forum.dfinity.org/t/migrate-non-stable-storage-to-stable-storage-on-single-canister/23521)

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

---

<div class="post-metadata">

**Author:** ![ielashi](https://sea1.discourse-cdn.com/flex023/user_avatar/forum.dfinity.org/ielashi/32/15704_2.png) [@ielashi](https://forum.dfinity.org/u/ielashi)\
**Post date:** [October 18, 2023, 6:53am UTC](https://forum.dfinity.org/t/stable-storage-not-working-as-expected/23822/4 "2023-10-18T06:53:21Z")

</div>

@rem.codes 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.

---

<div class="post-metadata">

**Author:** ![rem.codes](https://sea1.discourse-cdn.com/flex023/user_avatar/forum.dfinity.org/rem.codes/32/40260_2.png) [@rem.codes](https://forum.dfinity.org/u/rem.codes)\
**Post date:** [October 18, 2023, 10:11am UTC](https://forum.dfinity.org/t/stable-storage-not-working-as-expected/23822/5 "2023-10-18T10:11:32Z")

</div>

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!