# Core Concepts

This page explains the handles you work with in ToriiDB: the store, sessions, databases, entries, and the reserved key namespace.

## Store, Session, and Database

A `Store` owns 16 independent databases numbered `0` through `15`. Each database has its own `sync.RWMutex`, in-memory `map[string]*Entry`, directory `db_N/`, and load-once guard. A database is replayed from disk the first time any operation touches it.

| Handle | Created by | Shares | Owns |
|---|---|---|---|
| `Store` | `store.New(dir, apiKey...)` | nothing | all databases, embedder, background wait group, expiry timer |
| `Session` | `Store.Session()` | databases, embedder, wait group | its own selected database index |

`Select(index)` only changes the index of the handle it is called on and rejects values outside `0-15`. The index is a plain `int` with no lock, so concurrent callers must each use their own `Session`; the daemon creates one per request for this reason.

## Entries

```go
type Entry struct {
    Key       string
    Type      ValueType
    CreatedAt int64
    UpdatedAt *int64
    ExpireAt  *int64
    Vector    []float32
    // value and parsed are unexported
}
```

`Entry.Value()` returns the raw string. The unexported `parsed` field caches the decoded JSON value and is only changed through `setValue()` or `setParsed()`, so it never drifts from the raw string. `Get` returns a copy of the entry taken under the read lock.

## Reserved Namespace

Keys starting with `__torii:` hold internal data such as the embedding cache (`__torii:embed:<sha256>`). Scan-style operations skip them so they never leak into application results. Point lookups such as `GET __torii:...` are intentionally allowed for debugging.

## Related Pages

- [Value Types](/core-concepts-value-types)
- [Expiration](/core-concepts-expiration)
- [Errors](/core-concepts-errors)