Expand description
Lite Transaction File (LTX)
The LTX file format provides a way to store SQLite transactional data in a way that can be encrypted and compacted and is optimized for performance.
The Rust implementation is derived from the original Go implementation and mostly follows its design.
Until the library reaches version 1.0, the API is not considered stable and is subject to change.
File Format
An LTX file is composed of several sections:
- Header
- Page block
- Trailer
The header contains metadata about the file, the page block contains page frames, and the trailer contains checksums of the file and the database end state.
Header
The header provides information about the number of page frames as well as database information such as the page size and database size. LTX files can be compacted together so each file contains the transaction ID (TXID) range that it represents. A timestamp provides users with a rough approximation of the time the transaction occurred and the checksum provides a basic integrity check.
| Offset | Size | Description |
|---|---|---|
| 0 | 4 | Magic number. Always “LTX1”. |
| 4 | 4 | Flags. See below. |
| 8 | 4 | Page size, in bytes. |
| 12 | 4 | Size of DB after transaction, in pages. |
| 16 | 8 | Minimum transaction ID. |
| 24 | 8 | Maximum transaction ID. |
| 32 | 8 | Timestamp (Milliseconds since epoch) |
| 40 | 8 | Pre-apply DB checksum (CRC-ISO-64) |
| 48 | 8 | File offset in WAL, zero if journal |
| 56 | 8 | Size of WAL segment, zero if journal |
| 64 | 4 | Salt-1 from WAL, zero if journal or compacted |
| 68 | 4 | Salt-2 from WAL, zero if journal or compacted |
| 72 | 8 | ID of the node that created file, zero if unset |
| 80 | 20 | Reserved. |
Header flags
| Flag | Description |
|---|---|
| 0x00000001 | Data is compressed with LZ4 |
Page block
This block stores a series of page headers and page data.
| Offset | Size | Description |
|---|---|---|
| 0 | 4 | Page number. |
| 4 | N | Page data. |
Trailer
The trailer provides checksum for the LTX file data, a rolling checksum of the database state after the LTX file is applied, and the checksum of the trailer itself.
| Offset | Size | Description |
|---|---|---|
| 0 | 8 | Post-apply DB checksum (CRC-ISO-64) |
| 8 | 8 | File checksum (CRC-ISO-64) |
Structs
- A database checksum.
- An LTX file decoder.
- An LTX file encoder.
- An LTX file header.
- A database page number.
- A database page size in bytes.
- A position uniquely identifying a state of a database.
- An ID of a database transaction.
- An LTX file trailer.
Enums
Traits
- A trait for page checksum calculation.