> For the complete documentation index, see [llms.txt](https://firehose.streamingfast.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://firehose.streamingfast.io/references/cli-reference/merger.md).

# Merger

This page documents the configuration flags for the Merger component. For architectural concepts and how the Merger works, see [Merger Architecture](/firehose/architecture/components/merger.md).

## Starting the Merger

```bash
firecore start merger [flags]
```

## Core Configuration

| Flag                        | Description                              | Default  |
| --------------------------- | ---------------------------------------- | -------- |
| `--merger-grpc-listen-addr` | gRPC listening address for health checks | `:10012` |

## Storage Configuration

The Merger uses the common storage flags:

| Flag                               | Description                         | Default                                   |
| ---------------------------------- | ----------------------------------- | ----------------------------------------- |
| `--common-one-block-store-url`     | One-block files storage URL (input) | `file://{data-dir}/storage/one-blocks`    |
| `--common-merged-blocks-store-url` | Merged blocks storage URL (output)  | `file://{data-dir}/storage/merged-blocks` |
| `--common-forked-blocks-store-url` | Forked blocks storage URL           | `file://{data-dir}/storage/forked-blocks` |

## Timing Configuration

| Flag                                  | Description                         | Default |
| ------------------------------------- | ----------------------------------- | ------- |
| `--merger-time-between-store-lookups` | Polling interval for source store   | `1s`    |
| `--merger-time-between-store-pruning` | Interval between pruning operations | `1m0s`  |

## Pruning Configuration

| Flag                                 | Description                           | Default |
| ------------------------------------ | ------------------------------------- | ------- |
| `--merger-prune-forked-blocks-after` | Blocks to retain before pruning forks | `50000` |
| `--merger-delete-threads`            | Parallel threads for file deletion    | `8`     |

{% hint style="warning" %}
The pruning distance should be set large enough to handle chain reorganizations. The default of 50,000 blocks is conservative and suitable for most chains.
{% endhint %}

## Execution Control

| Flag                  | Description                      | Default |
| --------------------- | -------------------------------- | ------- |
| `--merger-stop-block` | Stop after merging to this block | (none)  |

## Health Check

The Merger exposes a gRPC health check endpoint:

```bash
grpcurl -plaintext localhost:10012 grpc.health.v1.Health/Check
```

The Merger always reports `SERVING` status when running - it doesn't have dynamic readiness conditions like other components.

## Example Usage

### Basic Local Setup

```bash
firecore start merger \
  --merger-grpc-listen-addr=":10012"
```

### With Cloud Storage

```bash
firecore start merger \
  --merger-grpc-listen-addr=":10012" \
  --common-one-block-store-url="s3://my-bucket/one-blocks" \
  --common-merged-blocks-store-url="s3://my-bucket/merged-blocks" \
  --common-forked-blocks-store-url="s3://my-bucket/forked-blocks"
```

### Processing to a Specific Block

```bash
firecore start merger \
  --merger-grpc-listen-addr=":10012" \
  --merger-stop-block=1000000
```