Note that `blocks_by_height` is also a bijection
@@ -613,9 +613,14 @@ Zcash structures are encoded using `ZcashSerialize`/`ZcashDeserialize`.
### Notes on Sled trees
-- The `hash_by_height` and `height_by_hash` trees provide the bijection between
+- The `hash_by_height` and `height_by_hash` trees provide a bijection between
block heights and block hashes. (Since the Sled state only stores finalized
- state, this is actually a bijection).
+ state, they are actually a bijection).
+
+- The `block_by_height` tree provides a bijection between block heights and block
+ data. There is no corresponding `height_by_block` tree: instead, hash the block,
+ and use `height_by_hash`. (Since the Sled state only stores finalized state,
+ they are actually a bijection).
- Blocks are stored by height, not by hash. This has the downside that looking
up a block by hash requires an extra level of indirection. The upside is
