Type Definition frame_system::pallet::StorageQueue

pub type StorageQueue<T: Config> = StorageValue<_GeneratedPrefixForStorageStorageQueue<T>, BoundedVec<(BlockNumberFor<T>, Option<u32>, Vec<(Option<T::AccountId>, EncodedTx)>), StorageQueueLimit>, ValueQuery>;

Storage queue is used for storing transactions in blockchain itself. Main reason for that storage entry is fact that upon VER block N execution it is required to fetch & executed transactions from previous block (N-1) but due to origin substrate design blocks & extrinsics are stored in rocksDB database that is not accessible from runtime part of the node (see Substrate architecture) what makes it impossible to properly implement block execution logic. As an solution blockchain runtime storage was selected as buffer for txs waiting for execution. Main advantage of such approach is fact that storage state is public so its impossible to manipulate data stored in there. Storage queue is implemented as double buffered queue - to solve problem of rare occasions where due to different reasons some txs that were included in block N are not able to be executed in a following block N+1 (good example is new session hook/event that by design consumes whole block capacity).

Overhead

Its worth to notice that storage queue adds only single storage write, as list of all txs is stored as single value (encoded list of txs) maped to single key (block number)

Storage Qeueue interaction

There are two ways to interact with storage queue:

• enqueuing new txs using Pallet::enqueue_txs inherent
• poping txs from the queue using Pallet::pop_txs that is exposed throught RuntimeApi call

Storage type is StorageValue with value type BoundedVec < (BlockNumberFor < T >, Option < u32 >, Vec < (Option < T :: AccountId >, EncodedTx) >), StorageQueueLimit, >.