electrs/doc/schema.md

Index Schema

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

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).