> ## Documentation Index
> Fetch the complete documentation index at: https://hexxladb.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Database

> Database lifecycle: Open, Close, Compact, and configuration

## Open

Opens or creates a database file. Applies WAL on startup for crash recovery.

```go theme={null}
db, err := hexxladb.Open("memory.db", &hexxladb.Options{
    EnableMVCC:         true,
    EmbeddingDimension: 384,
    DistanceMetric:     hexxladb.DistanceCosine,
})
if err != nil {
    log.Fatal(err)
}
defer db.Close()
```

## Close

Waits for in-flight transactions and closes the database. Idempotent for nil receiver.

```go theme={null}
err := db.Close()
```

## Compact

Copy-compacts an open database to a new file, reclaiming space from deleted records. Preserves all data including MVCC history.

```go theme={null}
err := db.Compact(ctx, "/tmp/compacted.db")
db.Close()
os.Rename("/tmp/compacted.db", originalPath)
db, _ = hexxladb.Open(originalPath, opts)
```

### CompactTo

Standalone compaction from source to destination:

```go theme={null}
err := hexxladb.CompactTo(ctx, srcPath, destPath, opts)
```

Destination inherits format version, MVCC flag, MaxValueBytes, and encryption from source. Encryption credentials must be supplied for encrypted sources.

## Configuration options

```go theme={null}
type Options struct {
    // MVCC and temporal
    EnableMVCC     bool
    MVCCRetention  MVCCRetention

    // Changelog
    ChangelogEnabled bool

    // Encryption
    EncryptionKey []byte
    Passphrase     string

    // Storage
    PageSize      int  // 4096, 8192, 16384, 65536
    MaxValueBytes int  // 512 to 1048576

    // Embeddings
    EmbeddingDimension int
    DistanceMetric     DistanceMetric

    // Hooks
    CellValidator  func(record.CellRecord) error
    AfterPutCell  func(record.CellRecord)
    AfterPutSeam  func(record.SeamRecord)
}
```

## Runtime properties

### PageSize

Returns the active page size in bytes (4096 default for new databases).

```go theme={null}
pageSize := db.PageSize()
```

### MaxValueBytes

Returns the effective per-database max value size in bytes from the file header.

```go theme={null}
maxValueBytes := db.MaxValueBytes()
```

### EmbeddingDimension

Returns the configured vector dimension (0 = disabled).

```go theme={null}
dim := db.EmbeddingDimension()
```

### EmbeddingMetric

Returns the configured distance metric.

```go theme={null}
metric := db.EmbeddingMetric()
```

## Storage limits

* **Maximum key length:** 256 bytes
* **Maximum value length:** Configurable via `MaxValueBytes` (512 to 1,048,576 bytes; default 8192)
* **Page size:** Configurable via `PageSize` (4096 to 65536 bytes; default 4096)
* **Compression:** DEFLATE always-on for values ≥ 64 bytes

## Errors

| Error                      | Description                                 |
| -------------------------- | ------------------------------------------- |
| `ErrCorruptDatabase`       | Open-time corruption (header/WAL)           |
| `ErrEncryptionKeyMismatch` | Wrong key/passphrase for encrypted database |

## See also

* [Transactions](/api/transactions) — Transaction methods
* [Options](/api/options) — Configuration options
* [Backups](/operations/backups) — Backup and compaction procedures