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# Algorand Specifications

A _State Delta_ represents the changes made to the Ledger’s state from one round to the next.

It is a compact data structure designed to efficiently update all state _Trackers_ after a block is committed. By recording only the parts of the state that were modified, it also simplifies block assembly and validation.

> For a formal definition of this structure, refer to the Algorand Ledger [normative specification](https://specs.algorand.co/ledger/ledger-apply-data#state-deltas).

In the `go-algorand` reference implementation, a _State Delta_ includes the following fields:

- `AccountStateDeltas`:

A set of [`Account State Deltas`](https://specs.algorand.co/ledger/ledger-account-state), collecting changes to accounts affected by the block, detailing how their states were modified.

- `KVMods`:

A key-value map of modified entries in the [Key Value Store](https://specs.algorand.co/ledger/ledger-applications#keyvalue-stores), represented as `(string → KvValueDelta)`.

- `TxIDs`:

A mapping of new transaction IDs to their `LastValid` round: `(txid → uint)`. This is used to update the TxTailTxTail and manage the transaction counter.

- `Txleases`:

A mapping `(TxLease → uint64)` of new transaction leases to their expiration rounds, also relevant to the TxTailTxTail mechanism.

- `Creatables`:

A mapping of data about newly created or deleted _“creatable entities”_ such as Applications and Assets.

- `*Hdr`:

A read-only reference to the header of the new block.

- `StateProofNext`:

Reflects any update to the `StateProofNextRound` in the block header. If the block includes a valid _State Proof_ transaction, this is set to the next round for a proof; otherwise, it’s set to 00.

- `PrevTimestamp`:

Stores the timestamp of the previous block as an integer.

- `AccountTotals`:

A snapshot of the updated account totals resulting from the changes in this _State_ _Delta_.