# Index Schema

The index is stored at a single RocksDB database using the following schema:

## Transaction outputs' index

Allows efficiently finding all funding transactions for a specific address:

|  Code  | Script Hash Prefix   | Funding TxID Prefix   |
| ------ | -------------------- | --------------------- |
| `b'O'` | `SHA256(script)[:8]` | `txid[:8]`            |

## Transaction inputs' index

Allows efficiently finding spending transaction of a specific output:

|  Code  | Funding TxID Prefix  | Funding Output Index  | Spending TxID Prefix  |
| ------ | -------------------- | --------------------- | --------------------- |
| `b'I'` | `txid[:8]`           | `uint16`              | `txid[:8]`            |


## Full Transaction IDs

In order to save storage space, we store the full transaction IDs once, and use their 8-byte prefixes for the indexes above.

|  Code  | Transaction ID    | Confirmed height |
| ------ | ----------------- |------------------|
| `b'T'` | `txid` (32 bytes) | `uint32`         |

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)).