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

# Replication Modes

> Full, incremental, and CDC — how a source reads.

A source reads data in one of three modes, declared as `ReplicationMode` in
its `ConnectorSpec`:

| Mode        | Constant          | What it does                                                                                                                                                                |
| ----------- | ----------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Full        | `ModeFull`        | Reads the entire resource from scratch every run                                                                                                                            |
| Incremental | `ModeIncremental` | Reads only what changed since a cursor from the previous run                                                                                                                |
| CDC         | `ModeCDC`         | Streams ordered changes (inserts/updates/deletes) from a checkpoint, via the source's [`ChangeSource`](/pages/connectors/building-a-connector/optional-interfaces) contract |

A connector advertises which modes it supports through `ConnectorSpec.Modes`
— not every source implements all three. Incremental and CDC extraction
build on the same checkpointing machinery described in [Integrity &
checkpoints](/pages/guides/concepts/integrity-and-checkpoints).

<Tip>
  PostgreSQL is a good example of a source that picks its read strategy
  dynamically even within a single mode — see [Postgres
  source](/pages/connectors/sources/postgres) for how it chooses between keyset,
  bitmap, and ctid-based scans.
</Tip>