# Index Schema

The index is stored at a single RocksDB database using the following column families.
Most of the data is stored in key-only DB rows (i.e. having empty values).

## Transaction outputs' index (`funding`)

Allows efficiently finding all funding transactions for a specific address:

|  Script Hash Prefix  | Confirmed Block Height |
| -------------------- | ---------------------- |
| `SHA256(script)[:8]` | `height as u32`        |

## Transaction inputs' index (`spending`)

Allows efficiently finding spending transaction of a specific output:

| Previous Outpoint Prefix | Confirmed Block Height |
| ------------------------ | ---------------------- |
| `txid[:8] as u64 + vout` | `height as u32`        |


## Transaction ID index (`txid`)

In order to save storage space, we map the 8-byte transaction ID prefix to its confirmed block height:

| Txid Prefix | Confirmed height |
| ----------- | ---------------- |
| `txid[:8]`  | `height as u32`  |

Note that this mapping allows us to use `getrawtransaction` RPC to retrieve actual transaction data from without `-txindex` enabled
(by explicitly specifying the [blockhash](https://github.com/bitcoin/bitcoin/commit/497d0e014cc79d46531d570e74e4aeae72db602d)).

## Headers (`headers`)

For faster loading, we store all block headers in RocksDB:

|    Serialized header    |
| ----------------------- |
| `header as BlockHeader` |

In addition, we also store the chain tip:

| Key |   |           Value          |
| --- | - | ------------------------ |
| `T` |   | `blockhash as BlockHash` |

## Configuration (`config`)

| Key |   |            Value            |
| --- | - | --------------------------- |
| `C` |   | `serialized config as JSON` |