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go-pq-cdc

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go-pq-cdc is lightweight and efficient Change Data Capture (CDC) system designed for PostgreSQL

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# go-pq-cdc [![Go Reference](https://pkg.go.dev/badge/github.com/Trendyol/go-dcp.svg)](https://pkg.go.dev/github.com/Trendyol/go-pq-cdc) [![Go Report Card](https://goreportcard.com/badge/github.com/Trendyol/go-pq-cdc)](https://goreportcard.com/report/github.com/Trendyol/go-pq-cdc) [![OpenSSF Scorecard](https://api.scorecard.dev/projects/github.com/Trendyol/go-pq-cdc/badge)](https://scorecard.dev/viewer/?uri=github.com/Trendyol/go-pq-cdc)

go-pq-cdc is designed to provide efficient and lightweight Change Data Capture (CDC) for PostgreSQL databases.
The architecture leverages PostgreSQL's built-in logical replication capabilities to capture changes in the database and
stream these changes to downstream systems, such as Kafka, Elasticsearch etc. The entire system is written in Golang,
ensuring low resource consumption and high performance.

[Debezium vs go-pq-cdc benchmark](./benchmark)

## Snapshot Feature

**Capture existing data before starting CDC!** The new snapshot feature enables initial data synchronization, ensuring downstream systems receive both historical and real-time data.

✨ **Key Highlights:**
- **Zero Data Loss**: Consistent point-in-time snapshot using PostgreSQL's `pg_export_snapshot()`
- **Chunk-Based Processing**: Memory-efficient processing of large tables
- **Smart Partitioning**: Auto-selects optimal strategy (Integer Range, CTID Block, or Offset)
- **Multi-Instance Support**: Parallel processing across multiple instances
- **Crash Recovery**: Automatic resume from failures
- **No Duplicates**: Seamless transition from snapshot to CDC
- **Snapshot Only Mode**: One-time data export without CDC (no replication slot required)
- **Protocol Flexibility**: `pgoutput` `proto_version` `1` and `2` support
- **Safe Streaming TX Handling**: Streamed rollback transactions are discarded correctly

📚 **[Read Full Documentation](docs/SNAPSHOT_FEATURE.md)** for detailed architecture, configuration, and best practices.
📚 **[Protocol Version & Streaming Transactions](docs/PROTO_VERSION_SUPPORT.md)** for `proto_version` behavior and migration guidance.

### Contents

- [go-pq-cdc   ](#go-pq-cdc---)
	- [Snapshot Feature](#snapshot-feature)
		- [Contents](#contents)
		- [Why?](#why)
		- [Usage](#usage)
		- [Examples](#examples)
		- [PostgreSQL User Permissions](#postgresql-user-permissions)
		- [Availability](#availability)
		- [TOAST Handling](#toast-handling)
		- [Heartbeat-based WAL Protection](#heartbeat-based-wal-protection)
			- [Replica Identity Requirement](#replica-identity-requirement)
		- [Configuration](#configuration)
		- [Protocol Version \& Streaming Transactions](#protocol-version--streaming-transactions)
		- [API](#api)
		- [Exposed Metrics](#exposed-metrics)
		- [Grafana Dashboard](#grafana-dashboard)
		- [Compatibility](#compatibility)
		- [Breaking Changes](#breaking-changes)

### Why?

CDC systems are crucial for real-time data synchronization, analytics, and event-driven architectures.
Our main goal is to build a cdc base library for faster and stateful systems.

#### Official
- [Postgresql to Elasticsearch Connector](https://github.com/Trendyol/go-pq-cdc-elasticsearch)
- [Postgresql to Kafka Connector](https://github.com/Trendyol/go-pq-cdc-kafka)

#### 3rd party
- [Postgresql to RabbitMQ Connector](https://github.com/ezeql/go-pq-cdc-rabbitmq)

### Usage

```sh
go get github.com/Trendyol/go-pq-cdc
```

```go
package main

import (
	"context"
	cdc "github.com/Trendyol/go-pq-cdc"
	"github.com/Trendyol/go-pq-cdc/config"
	"github.com/Trendyol/go-pq-cdc/pq/message/format"
	"github.com/Trendyol/go-pq-cdc/pq/publication"
	"github.com/Trendyol/go-pq-cdc/pq/replication"
	"github.com/Trendyol/go-pq-cdc/pq/slot"
	"log/slog"
	"os"
)

func main() {
	ctx := context.Background()
	cfg := config.Config{
		Host:      "127.0.0.1",
		Username:  "cdc_user",
		Password:  "cdc_pass",
		Database:  "cdc_db",
		DebugMode: false,
		Publication: publication.Config{
			CreateIfNotExists: true,
			Name: "cdc_publication",
			Operations: publication.Operations{
				publication.OperationInsert,
				publication.OperationDelete,
				publication.OperationTruncate,
				publication.OperationUpdate,
			},
			Tables: publication.Tables{publication.Table{
				Name:            "users",
				ReplicaIdentity: publication.ReplicaIdentityFull,
			}},
		},
		Slot: slot.Config{
			Name:                        "cdc_slot",
			CreateIfNotExists:           true,
			SlotActivityCheckerInterval: 3000,
			ProtoVersion:                2,
		},
		Metric: config.MetricConfig{
			Port: 8081,
		},
		Logger: config.LoggerConfig{
			LogLevel: slog.LevelInfo,
		},
	}

connector, err := cdc.NewConnector(ctx, cfg, Handler)
	if err != nil {
		slog.Error("new connector", "error", err)
		os.Exit(1)
	}

defer connector.Close()
	connector.Start(ctx)
}

func Handler(ctx *replication.ListenerContext) {
	switch msg := ctx.Message.(type) {
	case *format.Insert:
		slog.Info("insert message received", "new", msg.Decoded)
	case *format.Delete:
		slog.Info("delete message received", "old", msg.OldDecoded)
	case *format.Update:
		slog.Info("update message received", "new", msg.NewDecoded, "old", msg.OldDecoded)
	case *format.Truncate:
		slog.Info("truncate message received", "relations", msg.RelationOIDs, "cascade", msg.Cascade, "restartIdentity", msg.RestartIdentity)
	}

if err := ctx.Ack(); err != nil {
		slog.Error("ack", "error", err)
	}
}

```

### Examples

* [Simple](./example/simple)
* [Simple File Config](./example/simple-file-config)
* [Simple With Heartbeat](./example/simple-with-heartbeat)
* [Streaming Transactions](./example/streaming-transactions)
* [Snapshot Mode (Initial Data Capture)](./example/snapshot-initial-mode)
* [Snapshot Only Mode (One-Time Export)](./example/snapshot-only-mode)
* [Snapshot with Query Condition](./example/snapshot-with-query-condition)
* [Replica Identity Using Index](./example/replica-identity-using-index)
* [Replica Identity Nothing](./example/replica-identity-nothing)
* [PostgreSQL to Elasticsearch](https://github.com/Trendyol/go-pq-cdc-elasticsearch/tree/main/example/simple)
* [PostgreSQL to Kafka](https://github.com/Trendyol/go-pq-cdc-kafka/tree/main/example/simple)
* [PostgreSQL to PostgreSQL](./example/postgresql)
* [Partitioned Tables](./example/partitioned-table-mapping)

### PostgreSQL User Permissions

go-pq-cdc connects to PostgreSQL with a regular role. For most deployments you do **not** need a superuser. A dedicated role with the right grants is enough. The exact privileges depend on which features you enable.

Minimum role for streaming CDC against a fixed table list:

```sql
CREATE ROLE cdc_user WITH LOGIN REPLICATION PASSWORD 'change_me';

GRANT USAGE ON SCHEMA public TO cdc_user;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO cdc_user;
ALTER DEFAULT PRIVILEGES IN SCHEMA public
  GRANT SELECT ON TABLES TO cdc_user;
```

Add these grants when the corresponding feature is enabled:

| Feature | Extra grants needed |
|-----------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------|
| `publication.createIfNotExists: true` | `GRANT CREATE ON DATABASE <db> TO cdc_user;` so the publication can be created. |
| `slot.createIfNotExists: true` | `REPLICATION` role attribute (already in the example above). |
| Heartbeat with auto-created table | `GRANT CREATE ON SCHEMA <schema> TO cdc_user;` for the initial `CREATE TABLE`, plus `GRANT INSERT, UPDATE ON <heartbeat_table>` for the auto-managed singleton row. |
| Snapshot mode (initial / only) | `SELECT` on the source tables (already covered above). |
| Adding tables to an existing publication | The role must own the publication, e.g. `ALTER PUBLICATION cdc_publication OWNER TO cdc_user;`. |

Common failure modes when grants are missing:

- `must be superuser or replication role to start walsender` — role missing `REPLICATION`.
- `permission denied for schema <schema>` — missing `USAGE` on the schema.
- `permission denied to create publication` — missing `CREATE` on the database.
- `permission denied for table <heartbeat_table>` — heartbeat enabled but the role cannot `INSERT`/`UPDATE` the singleton row.

`pg_hba.conf` must also allow `replication` connections from the CDC host, for example:

```
host replication cdc_user 10.0.0.0/8 scram-sha-256
```

### Availability

The go-pq-cdc operates in passive/active modes for PostgreSQL change data capture (CDC). Here's how it ensures
availability:

* **Active Mode:** When the PostgreSQL replication slot (slot.name) is active, go-pq-cdc continuously monitors changes
  and streams them to downstream systems as configured.
* **Passive Mode:** If the PostgreSQL replication slot becomes inactive (detected via slot.slotActivityCheckerInterval),
  go-pq-cdc automatically captures the slot again and resumes data capturing. Other deployments also monitor slot
  activity,
  and when detected as inactive, they initiate data capturing.

This setup ensures continuous data synchronization and minimal downtime in capturing database changes.

### TOAST Handling

PostgreSQL does not send TOASTed column values during an update unless the TOASTed column itself is modified.
For example, if only a small field changes, large columns such as TEXT, JSONB, or BYTEA are sent as TOAST placeholders instead of real values.

To guarantee that UPDATE messages include full, correct data, go-pq-cdc automatically merges old and new tuples, restoring any missing TOASTed fields:

```go
if m.OldTupleData != nil {
    for i, col := range m.NewTupleData.Columns {
        // Toasted columns are not sent unless the column itself changed
        if col.DataType == tuple.DataTypeToast {
            m.NewTupleData.Columns[i] = m.OldTupleData.Columns[i]
        }
    }
}
```

### Heartbeat-based WAL Protection

Logical replication slots in PostgreSQL retain WAL segments until all consumers have confirmed they no longer need them.
In low-traffic databases, this can cause **WAL bloat** when other databases on the same Postgres instance generate a lot of
traffic while the CDC database itself remains mostly idle. In this situation the replication slot's `restart_lsn` and
`confirmed_flush_lsn` may lag far behind `pg_current_wal_lsn()`, preventing WAL segments from being recycled.

go-pq-cdc provides a **table-based heartbeat mechanism** for this scenario.
When `heartbeat.table.name` is configured, the connector:

- Creates the heartbeat table automatically (if missing).
- Ensures a single row exists.
- Periodically runs an internal `UPDATE` to generate small committed WAL records.
- Auto-acknowledges heartbeat events internally.
- Does not forward heartbeat events to your listener.

Each heartbeat:

- Produces a real transaction and COMMIT in the CDC database.
- Is decoded and acknowledged by go-pq-cdc via the replication stream.
- Advances the slot's `confirmed_flush_lsn` and, over time, `restart_lsn`, allowing PostgreSQL to safely recycle old WAL.

This makes WAL retention **predictable** even when application traffic on the CDC database is very low, while other
databases on the same instance are generating heavy write load.

> **Heartbeat only cleans WAL when its writes flow through the replication slot.**
>
> The heartbeat table must satisfy **both** conditions below — otherwise the auto-`UPDATE`s commit successfully but the slot never decodes them, `confirmed_flush_lsn` stays frozen, and WAL keeps growing as if heartbeat were disabled:
>
> 1. The heartbeat table is listed in `publication.tables`. If it is not part of the publication the change is filtered out before reaching the slot.
>    The connector validates this at startup for selective publications and returns an error if the heartbeat table is missing.
> 2. The heartbeat table has a `REPLICA IDENTITY` that allows the auto-`UPDATE` to be decoded — `DEFAULT` (the auto-created table already has a primary key, so this works out of the box) or `FULL`. `REPLICA IDENTITY NOTHING` will silently break WAL advancement because the `UPDATE` cannot be decoded by `pgoutput`.
>
> Use a dedicated heartbeat table — never reuse a business table.

```yaml
heartbeat:
  table:
    name: "my_heartbeat"
    schema: "public"
  interval: 100ms
```

Make sure the heartbeat table is included in the publication, for example:

```go
Publication: publication.Config{
    Name:              "cdc_publication",
    CreateIfNotExists: true,
    Tables: publication.Tables{
        publication.Table{Name: "users"},
        publication.Table{Name: "my_heartbeat"}, // must be present
    },
},
```

#### Migration (breaking change)

Before:

```yaml
heartbeat:
  enabled: true
  query: "INSERT INTO heartbeat_table(txt) VALUES ('hb')"
  interval: 5s
```

After:

```yaml
heartbeat:
  table:
    name: "heartbeat_table"
    schema: "public"
  interval: 100ms
```

You can run [Simple With Heartbeat](./example/simple-with-heartbeat) example.

#### Upgrade: heartbeat table must be in publication

If you use heartbeat with a **selective publication** (`publication.tables` is non-empty and the publication is not `FOR ALL TABLES`), the connector now **fails at startup** when the heartbeat table is missing from `publication.tables`.

Previously, this misconfiguration could still start successfully, but heartbeat writes would not reach the replication slot and WAL retention would not improve.

Before upgrading, add the heartbeat table to your publication config (or switch to a `FOR ALL TABLES` publication):

```yaml
publication:
  name: cdc_publication
  createIfNotExists: true
  tables:
    - name: users
      schema: public
    - name: my_heartbeat
      schema: public
```

#### Replica Identity Requirement

For this TOAST reconstruction to work, PostgreSQL must send the old tuple.
This requires setting the table's replica identity to FULL:

`ALTER TABLE your_table REPLICA IDENTITY FULL;`

- With `REPLICA IDENTITY DEFAULT`, PostgreSQL only sends primary keys for updates/deletes.
- In that mode, old tuple values (including TOASTed fields) are not provided.
- Therefore, `FULL` is required to correctly handle TOASTed columns in CDC.

For large tables, `REPLICA IDENTITY USING INDEX` can be a better trade-off for network traffic and matching performance:

- `FULL` sends old values of all columns (`O` tuple data).
- `USING INDEX` sends only old values of the columns from the selected unique index (`K` tuple data).
- This reduces payload size, but unlike `FULL`, old non-index columns are not available.

You can run [Replica Identity Using Index](./example/replica-identity-using-index) for a minimal `USING INDEX` setup.

`REPLICA IDENTITY NOTHING` is best paired with insert-only publications because PostgreSQL does not provide old-row data for updates and deletes in that mode.

You can run [Replica Identity Nothing](./example/replica-identity-nothing) for an insert-only `NOTHING` example.

### Configuration

| Variable | Type | Required | Default | Description | Options |
|-----------------------------------------|:--------:|:--------:|:-------:|-------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------|
| `host` | string | yes | - | PostgreSQL host | Should be a valid hostname or IP address. Example: `localhost`. |
| `username` | string | yes | - | PostgreSQL username | Should have sufficient privileges to perform required database operations. |
| `password` | string | yes | - | PostgreSQL password | Keep secure and avoid hardcoding in the source code. |
| `database` | string | yes | - | PostgreSQL database | The database must exist and be accessible by the specified user. |
| `debugMode` | bool | no | false | For debugging purposes | Enables pprof for trace. |
| `metric.port` | int | no | 8080 | Set API port | Choose a port that is not in use by other applications. |
| `logger.logLevel` | string | no | info | Set logging level | [`DEBUG`, `WARN`, `INFO`, `ERROR`] |
| `logger.logger` | Logger | no | slog | Set logger | Can be customized with other logging frameworks if `slog` is not used. |
| `publication.createIfNotExists` | bool | no | - | Create publication if not exists. Otherwise, return `publication is not exists` error. | |
| `publication.name` | string | yes | - | Set PostgreSQL publication name | Should be unique within the database. |
| `publication.operations` | []string | yes | - | Set PostgreSQL publication operations. List of operations to track; all or a subset can be specified. | **INSERT:** Track insert operations. **UPDATE:** Track update operations. **DELETE:** Track delete operations. |
| `publication.tables` | []Table | yes | - | Set tables which are tracked by data change capture | Define multiple tables as needed. |
| `publication.tables[i].name` | string | yes | - | Set the data change captured table name | Must be a valid table name in the specified database. |
| `publication.tables[i].replicaIdentity` | string | yes | - | Set the data change captured table replica identity [`DEFAULT`, `FULL`, `NOTHING`, `USING INDEX`] | **DEFAULT:** Captures primary key old values. **FULL:** Captures all old row columns. **NOTHING:** Captures no old row data (typically insert-only scenarios; update/delete matching can fail). **USING INDEX:** Captures old values from a chosen unique index. Applied independently of `createIfNotExists`: if set, the connector runs `ALTER TABLE ... REPLICA IDENTITY` when the table's current identity differs (requires DDL privilege on the table). |
| `publication.tables[i].replicaIdentityIndex` | string | no* | - | Unique index name used when `replicaIdentity` is `USING INDEX`. | Required only for `USING INDEX`, ignored otherwise. |
| `publication.tables[i].schema` | string | no | public | Set the data change captured table schema name | Must be a valid table name in the specified database. |
| `publication.tables[i].columns` | []string | no | - | Only include these columns in replication and snapshotting | Must not be set when `replicaIdentity` is `FULL`; only compatible with `DEFAULT`. |
| `publication.tables[i].partitioned` | bool | no | false | Flag for replicating a partitioned table via the root table name instead of listing out the individual table parts. Sets `publish_via_partition_root = true` when creating the publication. | Only avaible with PostgreSQL 13+. This is a publication-wide setting, Setting any table with this will include it for all tables in the publication. |
| `publication.tables[i].snapshotPartitionStrategy` | string | no | auto | Override partition strategy for snapshot | **auto:** Auto-detect best strategy (sparse integer PKs fall back to `ctid_block`). **integer_range:** Sequential integer PKs. **ctid_block:** String/UUID/hash/sparse PKs. **offset:** Slow fallback. |
| `publication.tables[i].queryCondition` | string | no | - | Per-table query condition for snapshot queries (SNAPSHOT-ONLY, does NOT affect CDC). Takes precedence over global `snapshot.queryCondition`. | Example: `"deleted_at IS NULL"`. Appended to WHERE clause with `AND`. |
| `slot.createIfNotExists` | bool | no | - | Create replication slot if not exists. Otherwise, return `replication slot is not exists` error. | |
| `slot.name` | string | yes | - | Set the logical replication slot name | Should be unique and descriptive. |
| `slot.slotActivityCheckerInterval` | int | no | 1000 | Set the slot activity check interval time in milliseconds | Specify as an integer value in milliseconds (e.g., `1000` for 1 second). |
| `slot.protoVersion` | int | no | 2 | `pgoutput` protocol version used in `START_REPLICATION` | `1`: PostgreSQL 10+ compatibility, no streaming transaction protocol messages. `2`: PostgreSQL 14+, enables streaming/messages options. |
| `snapshot.enabled` | bool | no | false | Enable initial snapshot feature | When enabled, captures existing data before starting CDC. |
| `snapshot.mode` | string | no | never | Snapshot mode: `initial`, `never`, or `snapshot_only` | **initial:** Take snapshot only if no previous snapshot exists, then start CDC. **never:** Skip snapshot, start CDC immediately. **snapshot_only:** Take snapshot and exit (no CDC, no replication slot required). |
| `snapshot.chunkSize` | int64 | no | 8000 | Number of rows per chunk during snapshot | Adjust based on table size. Larger chunks = fewer chunks but more memory per chunk. |
| `snapshot.claimTimeout` | duration | no | 30s | Timeout to reclaim stale chunks | If a worker doesn't send heartbeat for this duration, chunk is reclaimed by another worker. |
| `snapshot.heartbeatInterval` | duration | no | 5s | Interval for worker heartbeat updates | Workers send heartbeat every N seconds to indicate they're processing a chunk. |
| `snapshot.instanceId` | string | no | auto | Custom instance identifier (optional) | Auto-generated as `hostname-pid` if not specified. Useful for tracking workers. |
| `snapshot.tables` | []Table | no* | - | Tables to snapshot (required for `snapshot_only` mode, optional for `initial` mode) | **snapshot_only:** Must be specified here (independent from publication). **initial:** If specified, must be a subset of publication tables. If not specified, all publication tables are snapshotted. |
| `snapshot.queryCondition` | string | no | - | Global query condition applied to all snapshot queries (SNAPSHOT-ONLY, does NOT affect CDC). Per-table `queryCondition` overrides this value. | Example: `"status = 'active'"`. Appended to WHERE clause with `AND`. |
| `heartbeat.table.name` | string | no | - | Name of the heartbeat table. Setting this enables heartbeat behavior. | Table is auto-created if missing and should be included in `publication.tables` if you want it replicated. |
| `heartbeat.table.schema` | string | no | public | Schema of the heartbeat table. | Defaults to `public` when omitted. |
| `heartbeat.interval` | duration | no | 100ms | Interval between heartbeat updates when heartbeat is configured. Must be greater than 0. | Any valid Go duration string (e.g. `100ms`, `1s`, `5s`, `1m`). |
| `extensionSupport.enableTimescaleDB` | bool | no | false | Enable support for TimescaleDB hypertables. Ensures proper handling of compressed chunks during replication. | |

### API

| Endpoint             | Description                                                                               |
|----------------------|-------------------------------------------------------------------------------------------|
| `GET /status`        | Returns a 200 OK status if the client is able to ping the PostgreSQL server successfully. |
| `GET /metrics`       | Prometheus metric endpoint.                                                               |
| `GET /debug/pprof/*` | (Only for `debugMode=true`) [pprof](https://pkg.go.dev/net/http/pprof)                    |

### Protocol Version & Streaming Transactions

`go-pq-cdc` now supports both `pgoutput` protocol versions:

- **`slot.protoVersion: 1`**
  - Works with PostgreSQL 10+
  - Starts replication with `proto_version '1'`
  - Does not request `messages 'true'` or `streaming 'true'`
  - Best choice for older PostgreSQL versions or simpler CDC setups

- **`slot.protoVersion: 2` (default)**
  - Requires PostgreSQL 14+
  - Starts replication with `proto_version '2'`, `messages 'true'`, and `streaming 'true'`
  - Supports streamed in-progress transactions (`STREAM START/STOP/COMMIT/ABORT`)

Streaming behavior for `proto_version: 2`:

- Streamed DML events are buffered per transaction XID.
- Events are emitted only on `STREAM COMMIT`.
- `STREAM ABORT` discards all buffered events for that transaction.
- This prevents rolled-back streamed transactions from leaking to consumers.

### Exposed Metrics

The client collects relevant metrics related to PostgreSQL change data capture (CDC) and makes them available at
the `/metrics` endpoint.

| Metric Name                                         | Description                                                                                           | Labels         | Value Type |
|-----------------------------------------------------|-------------------------------------------------------------------------------------------------------|----------------|------------|
| go_pq_cdc_update_total                              | The total number of `UPDATE` operations captured on specific tables.                                  | slot_name, host| Counter    |
| go_pq_cdc_delete_total                              | The total number of `DELETE` operations captured on specific tables.                                  | slot_name, host| Counter    |
| go_pq_cdc_insert_total                              | The total number of `INSERT` operations captured on specific tables.                                  | slot_name, host| Counter    |
| go_pq_cdc_cdc_latency_current                       | The current latency in capturing data changes from PostgreSQL, in nanoseconds.                       | slot_name, host| Gauge      |
| go_pq_cdc_cdc_latency_current_milliseconds          | The current latency in capturing data changes from PostgreSQL, in milliseconds.                      | slot_name, host| Gauge      |
| go_pq_cdc_process_latency_current                   | The current latency in processing the captured data changes, in nanoseconds.                         | slot_name, host| Gauge      |
| go_pq_cdc_process_latency_current_milliseconds      | The current latency in processing the captured data changes, in milliseconds.                        | slot_name, host| Gauge      |
| go_pq_cdc_replication_slot_slot_confirmed_flush_lsn | The last confirmed flush Log Sequence Number (LSN) in the PostgreSQL replication slot.                | slot_name, host| Gauge      |
| go_pq_cdc_replication_slot_slot_current_lsn         | The current Log Sequence Number (LSN) being processed in the PostgreSQL replication slot.             | slot_name, host| Gauge      |
| go_pq_cdc_replication_slot_slot_is_active           | Indicates whether the PostgreSQL replication slot is currently active (1 for active, 0 for inactive). | slot_name, host| Gauge      |
| go_pq_cdc_replication_slot_slot_lag                 | The replication lag measured by the difference between the current LSN and the confirmed flush LSN.   | slot_name, host| Gauge      |
| go_pq_cdc_replication_slot_slot_retained_wal_size   | The size of Write-Ahead Logging (WAL) files retained for the replication slot in bytes.               | slot_name, host| Gauge      |
| go_pq_cdc_snapshot_in_progress                      | Indicates whether snapshot is currently in progress (1 for active, 0 for inactive).                   | slot_name, host| Gauge      |
| go_pq_cdc_snapshot_total_tables                     | Total number of tables to snapshot.                                                                    | slot_name, host| Gauge      |
| go_pq_cdc_snapshot_total_chunks                     | Total number of chunks to process across all tables.                                                   | slot_name, host| Gauge      |
| go_pq_cdc_snapshot_completed_chunks                 | Number of chunks completed in snapshot.                                                                | slot_name, host| Gauge      |
| go_pq_cdc_snapshot_total_rows                       | Total number of rows read during snapshot.                                                             | slot_name, host| Counter    |
| go_pq_cdc_snapshot_duration_seconds                 | Duration of the last snapshot operation in seconds.                                                    | slot_name, host| Gauge      |
| runtime metrics                                     | [Prometheus Collector](https://golang.bg/src/runtime/metrics/description.go)                          | N/A            | N/A        |

### Grafana Dashboard

Import the grafana dashboard [json file](./grafana/dashboard.json).
![Dashboard](https://raw.githubusercontent.com/Trendyol/go-pq-cdc/main/grafana/dashboard.png)

### Compatibility

| go-pq-cdc Version | slot.protoVersion | Minimum PostgreSQL Server Version | Notes |
|-------------------|-------------------|-----------------------------------|-------|
| 0.0.2 or higher   | 1                 | 10                                | No streaming transaction protocol messages |
| 0.0.2 or higher   | 2                 | 14                                | Supports streamed in-progress transactions |

### Breaking Changes

| Date taking effect | Version | Change | How to check |
|--------------------|---------|--------|--------------|
| Next release       | TBD     | Startup fails when heartbeat is enabled but the heartbeat table is missing from a selective publication. | Ensure `publication.tables` includes your heartbeat table, or use a `FOR ALL TABLES` publication. See [Upgrade: heartbeat table must be in publication](#upgrade-heartbeat-table-must-be-in-publication). |

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