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# Algorand Specifications

Each _Tracker_ exposes tracker-specific APIs to access the state it maintains.

> Important
>
> **IMPLEMENTATION:**
>
> Tracker [reference implementation](https://github.com/algorand/go-algorand/blob/df0613a04432494d0f437433dd1efd02481db838/ledger/tracker.go#L156-L169).

Trackers can access the Ledger via a restricted interface called `ledgerForTracker`,  
which grants access to the Ledger’s SQLite database, recent blocks, and other read-only  
functionality.

In the other direction, the Ledger communicates with Trackers using the `ledgerTracker`  
interface, which includes the following key methods:

- `loadFromDisk(ledgerForTracker)`

Initializes the state of the Tracker. The Tracker can use the `ledgerForTracker`  
  argument to:
  - Load persistent state (e.g., for the accounts database),
  - Query recent blocks, if its state depends only on recent history (e.g., the one  
    that tracks recently committed transactions).
- `newBlock(rnd, delta)`

Notifies the Tracker of a newly added block at round `rnd`. The accompanying `delta`  
  parameter contains the state changes introduced by this block (see [block evaluation\  
  section](https://specs.algorand.co/ledger/non-normative/ledger-nn-block-commitment)).

- `committedUpTo(rnd)`

Informs the Tracker that all blocks up to and including `rnd` are written to persistent  
storage. This call is crucial for stateful trackers, as it ensures correct state  
recovery and enables responses to queries about older blocks if recent uncommitted  
ones are lost after a crash.

- `close()`

Releases any resources or memory held by the Tracker.

The reference implementation ensures that all updates to Trackers are _thread-safe_  
using a _reader-writer lock_.