ic-memory 0.35.1

Durable stable-memory allocation governance for Internet Computer canisters
Documentation

Jump to: What it does · Why it matters · Is it useful? · How it works · Choose an integration style · Quick start · Troubleshooting · Advanced integration

What it does

ic-memory is a safety system for an Internet Computer application's persistent data.

When an application is upgraded, its code changes but its stored data remains. Each database, log, queue, or settings store must reconnect to the same storage location it used before. If two stores are accidentally swapped, the new code can interpret one kind of data as another.

ic-memory remembers which storage location belongs to each named store. Before the application opens any of those stores, it checks the new layout against the saved ownership records. A conflicting upgrade stops with an error instead of opening the wrong data.

ic-memory protects the connection between a store and its storage location. It is not a backup system, a database schema migrator, or a data validator.

Why this matters

Imagine that version 1 of an application stores users and orders separately:

Users  -> storage location 100
Orders -> storage location 101

A later version accidentally reverses those locations:

Users  -> storage location 101
Orders -> storage location 100

The diagram below shows the same mistake and the point where ic-memory intervenes:

The program can still compile, and the upgrade can still install. Without an allocation check, it may then read order records as users and user records as orders. ic-memory detects the changed ownership before either location is opened.

This protection matters because a stable-memory location is a durable part of an application's storage layout, even though it can look like an ordinary number in source code.

Is it useful for my application?

ic-memory is most useful for frameworks, generated canisters, multi-store applications, plugin systems, and canister families that evolve over time.

How it works

The lifecycle has three parts:

  1. Name each store. The application gives every persistent store a permanent identity, such as app.users.v1.
  2. Remember its location. On the first successful installation, ic-memory records which storage location belongs to each name.
  3. Check before opening. On every installation or upgrade, the new application version declares the layout it expects. ic-memory compares that layout with the remembered one before any application store opens.

If the layouts agree, the application receives permission to open its stores. If a known name moved, a location changed owner, or another allocation rule is broken, the check returns an error and ic-memory grants no permission to open application stores.

This check-and-record operation is called bootstrap. Its important guarantee is validation before open: a diagnostic report or an uncommitted validation result cannot grant access to a store. The runtime publishes permission only after the allocation ledger has been recovered, checked, and durably updated.

The ledger stores one current record per allocated identity and the latest schema metadata. It keeps no per-upgrade or schema-change history. Omitted and retired identities retain their IDs to prevent accidental reuse. A commit counter and two protected commit slots support stale-proof checks and corruption detection.

What happens when a check fails?

Bootstrap returns an error before application stores are opened. ic-memory does not silently repair, move, discard, or reinterpret a conflicting allocation. A failed attempt publishes no permission to open stores.

Treat the error as an upgrade-safety signal: keep the existing stable memory, inspect the requested keys, host namespace grants, exclusions, policy and diagnostics, then correct the new application version. Do not erase the allocation ledger or replace it with an empty one to make the error disappear. See the symptom-based troubleshooting guide for safe next steps.

What it protects

Retiring a store does not make its old location reusable. That tombstone is intentional: reusing the location could make a rollback open unrelated data.

Terminology

  • A stable key is a permanent store name, such as app.orders.v1.
  • A memory ID is the physical MemoryManager location behind that key.
  • An authority names the linked component requesting a key.
  • A namespace grant admits that authority's keys under a host-selected prefix.
  • The allocation pool contains eligible application IDs shared by all owners.
  • Bootstrap recovers, admits, resolves, validates and commits before opening.
  • The allocation ledger retains key-to-ID bindings and retirement tombstones.

The application owns one pool and one bootstrap per backing memory. Libraries contribute key requests, verify that the host included them, and open their committed keys. Owner labels are current host policy; they are not persisted ownership history, caller authentication or a sandbox for linked code.

Quick start for developers

Add the crate:

[dependencies]
ic-memory = "0.35.1"

ic-memory re-exports its exact ic-stable-structures dependency through ic_memory::ic_stable_structures. Import collections, backing memories, and traits through that namespace so their types match the runtime:

use ic_memory::{
    RuntimeMemory,
    ic_stable_structures::{Cell, DefaultMemoryImpl},
};

type CounterStore = Cell<u64, RuntimeMemory<DefaultMemoryImpl>>;

A separate ic-stable-structures dependency is unnecessary for those imports.

Declare keys; let the host allocate

Components name their owner and permanent keys without choosing IDs:

const MEMORY_AUTHORITY: &str = "example_app";
ic_memory::ic_memory_declaration!(
    authority = MEMORY_AUTHORITY,
    key = "example_app.users.v1",
);

fn initialize_stable_storage() -> Result<(), Box<dyn std::error::Error>> {
    let pool = ic_memory::MemoryAllocationPool::new(
        vec![ic_memory::MemoryAuthority::new(MEMORY_AUTHORITY, "example_app.")?],
        vec![],
    )?;
    ic_memory::bootstrap_default_memory_manager(&pool)?;
    let users = ic_memory::open_default_memory_manager_memory("example_app.users.v1")?;
    drop(users);
    Ok(())
}

Call this host bootstrap from initialization and post-upgrade before deferred stable collections open. Hosts needing admission or custom bucket geometry use the policy or configuration bootstrap helpers with the same explicit pool.

Known keys retain their committed IDs. New requests are sorted by key and take the lowest unclaimed ID in the common pool. Current, omitted, reserved and retired records occupy their IDs permanently. Namespace grants do not divide space between components. Exhaustion rejects the entire attempt.

See examples/key_only.rs and examples/composed_host.rs.

Applications composed from several libraries

Every linked crate contributes requests to one immutable registry. The host admits disjoint namespaces for their named owners and supplies explicit physical exclusions for unmanaged MemoryManager clients. All components draw from the same remaining pool. The application bootstraps the combined layout once.

Libraries adopting an already bootstrapped host can verify that all of their requirements were included without rerunning bootstrap or replacing the host's policy:

fn adopt_host() -> Result<(), Box<dyn std::error::Error>> {
    let requirements = ic_memory::sealed_declaration_snapshot()?;
    ic_memory::verify_default_memory_manager_authority(
        &requirements,
        "library_name",
    )?;
    Ok(())
}

Duplicate keys, overlapping namespace grants, foreign owner claims and excluded historical IDs fail before application stores open. Populated IDs without a ledger record must be explicitly excluded by the host; bootstrap refuses to infer custody from stored bytes.

The default runtime reserves IDs 0..=9 and keys under ic_memory.* for its own governance records. ID 0 contains the allocation ledger. Application code may use IDs through 254; ID 255 is the upstream unallocated sentinel and can never be declared.

Stable keys

A stable key names the durable identity of a store, not its current numeric location:

namespace.component.store_or_role.vN

use ic_memory::StableKey;

StableKey::parse("app.orders.v1").expect("app key");
StableKey::parse("myapp.audit_log.v1").expect("app key");
StableKey::parse("icydb.test_db.users.data.v1").expect("database key");

Changing a key creates a new allocation identity. If the durable store is still the same store, keep its key and change its optional diagnostic schema metadata instead.

Frequently asked questions

No. It validates allocation identity. Schema and data migrations remain the application's responsibility.

No. Keep a separate backup and disaster-recovery plan. ic-memory fails closed when its allocation metadata cannot be recovered safely.

Bootstrap returns an error and publishes no open capability. Fix the proposed layout or policy; do not erase the ledger to bypass the conflict.

No. Retirement is a permanent tombstone so a future version or rollback cannot mistake unrelated data for the retired store.

No. One owner bootstraps each concrete runtime. Libraries verify their requirements against the host's committed layout and open only their keys.

Each library declares permanent keys and its owner label. The host admits the namespace and owns physical exclusions; Memory assigns IDs and retains them.

Yes, provided its key is new, the host admits its namespace and owner, the common pool has space, and the complete layout passes admission and validation.

Operations and advanced integration

ic-memory is pre-1.0 infrastructure extracted from Canic. Current releases use the current API and durable format only; earlier pre-1.0 wire formats are not a compatibility target.