> For the complete documentation index, see [llms.txt](https://dzhelezov.gitbook.io/hydra/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dzhelezov.gitbook.io/hydra/hydra-processor.md).

# Hydra Processor

Hydra processor is a client-side 'sink' tool used to fetch substrate events from a Hydra indexer. It sequentially applies the event handlers one by one in the order the events have been emitted.

## Commands

* [`hydra-processor help [COMMAND]`](/hydra/hydra-processor.md#hydra-processor-help-command)
* [`hydra-processor migrate`](/hydra/hydra-processor.md#hydra-processor-migrate)
* [`hydra-processor run`](/hydra/hydra-processor.md#hydra-processor-run)

## `hydra-processor help [COMMAND]`

display help for hydra-processor

```
display help for <%= config.bin %>

USAGE
  $ hydra-processor help [COMMAND]

ARGUMENTS
  COMMAND  command to show help for

OPTIONS
  --all  see all commands in CLI
```

*See code:* [*@oclif/plugin-help*](https://github.com/oclif/plugin-help/blob/v2.2.3/src/commands/help.ts)

## `hydra-processor migrate`

```
undefined

USAGE
  $ hydra-processor migrate

OPTIONS
  -e, --env=env  Path to a file with environment variables
```

## `hydra-processor run`

```
undefined

USAGE
  $ hydra-processor run

OPTIONS
  -e, --env=env            Path to a file with environment variables
  -m, --manifest=manifest  Manifest file
  --id=id                  ID of the processor (useful for multi-processor setups)
  --indexer=indexer        Indexer URL to source events
```

## Qickstart

Before the first run, the processor should set up auxiliary database tables required for its work:

```
hydra-processor migrate
```

Then `hydra-processor` can be run against the manifest file (by default, it looks up `manifest.yml` in the current folder)

```
hydra-processor run -m <path/to/manifest> -e <path to a file with env variables>
```

## Environment variables

Hydra processor requires a manifest file and certain environment variables to be set.

| Variable               |       Default      | Required |                                                       Description |
| ---------------------- | :----------------: | -------: | ----------------------------------------------------------------: |
| INDEXER\_ENDPOINT\_URL |          -         |  **Yes** | Hydra indexer endpoint to source the raw event and extrinsic data |
| MANIFEST\_PATH         |    manifest.yml    |   **No** |                                         Path to the manifest file |
| DB\_NAME               |          -         |  **Yes** |                                                     Database name |
| DB\_PORT               |          -         |  **Yes** |                                                     Database port |
| DB\_HOST               |          -         |  **Yes** |                                                     Database host |
| DB\_USER               |          -         |  **Yes** |                                                     Database user |
| DB\_PASS               |          -         |  **Yes** |                                                 Database password |
| PROMETHEUS\_PORT       |        3000        |   **No** |             A prometheus metrics endpoint is started at this port |
| POLL\_INTERVAL\_MS     | 1 sec (60000 msec) |   **No** |          How often the processor polls the indexer for new blocks |

The required variables can either be set externally or loaded from a file using the `-e` flag, e.g.:

```
hydra-processor migrate -e .env
```

## Manifest file

The manifest file describes which and how the events and extrinsics should be processed. Here is an example for Kusama blockchain:

```
version: '0.1'
description: Test manifest
repository: https://github.com/
## currently only these settings for the datasouce section are accepted
dataSource:
  kind: substrate 
  chain: kusama
  indexerVersion: '0.0.4'
# compiled model classes generated by hydra-cli codegen from the input schema 
entities:
  - mappings/lib/generated/**/*.model.js
mappings:
  hydraCommonVersion: '0.0.3'
  # process only blocks with height >= 1M 
  blockInterval: '[1000000,]'
  # js module that exports the handler functions 
  mappingsModule: mappings/lib/mappings
  # additinal libraries the processor loads
  # typically it is a module with event and extrinsic types generated by hydra-typegen 
  imports:
    - mappings/lib/mappings/generated/types
  eventHandlers:
  # event name
    - event: balances.Transfer 
  # function handler name with the argument types
      handler: balancesTransfer(DatabaseManager, Balances.TransferEvent)
  extrinsicHandlers:
    # infer defaults here
    #- extrinsic: Balances.Transfer 
    #- extrinsic: Sudo.batchCall 
    #  handler: handleSudoCall(DatabaseManager,SubstrateEvent)
  preBlockHooks:
  postBlockHooks:
```