This modifies the utxoset in the database and related UtxoViewpoint to
store and work with unspent transaction outputs on a per-output basis
instead of at a transaction level.
The primary motivation is to simplify the code, pave the way for a
utxo cache, and generally focus on optimizing runtime performance.
The tradeoff is that this approach does somewhat increase the size of
the serialized utxoset since it means that the transaction hash is
duplicated for each output as a part of the key and some additional
details are duplicated in each output. The details duplicated in each
output include flags encoded into a single byte that specify whether the
containing transaction is a coinbase, whether the containing transaction
has an expiry, and the transaction type. Additionally, the containing
block height and index are stored in each output.
However, in practice, the size difference isn't all that large, disk
space is relatively cheap, certainly cheaper than memory, and it is much
more important to provide more efficient runtime operation since that is
the ultimate purpose of the daemon.
While performing this conversion, it also simplifies the code to remove
the transaction version information from the utxoset as well as the
spend journal. The logic for only serializing it under certain
circumstances is complicated, and it was only used for the gettxout RPC,
where it has already been removed.
The utxo set and spend journal in the database are automatically
migrated to the new format with this commit and it is possible to
interrupt and resume the migration process.
Finally, it also updates all references and tests that previously dealt
with transaction hashes to use outpoints instead.
An overview of the changes are as follows:
- Remove transaction version from both spent and unspent output entries
- Update utxo serialization format to exclude the version
- Update spend journal serialization format to exclude the version
- Convert UtxoEntry to represent a specific utxo instead of a
transaction with all remaining utxos
- Optimize for memory usage with an eye toward a utxo cache
- Combine fields such as whether the containing transaction is a
coinbase, whether the containing transaction has an expiry, and
the transaction type into a single byte
- Align entry fields to eliminate extra padding since ultimately
there will be a lot of these in memory
- Introduce a free list for serializing an outpoint to the database
key format to significantly reduce pressure on the GC
- Update entries to be keyed by a <hash><tree><output index> outpoint
rather than just a tx hash
- Update all related functions that previously dealt with transaction
hashes to accept outpoints instead
- Update all callers accordingly
- Only add individually requested outputs from the mempool when
constructing a mempool view
- Modify the spend journal to always store the encoded flags with every
spent txout
- Combine fields such as whether the containing transaction is a
coinbase, whether the containing transaction has an expiry, and the
transaction type into a single byte
- Use 4 bits instead of 3 for the transaction type to be consistent
with utxos. The extra bit was already unused so this doesn't take
any additional space
- Remove the fully spent flag
- Introduce ticketMinOuts in place of stakeExtra
- Renamed stakeExtra as ticketMinOuts and updated all comments to make
the purpose of the field clearer
- Only store ticketMinOuts for ticket submission outputs
- Add TicketMinimalOutputs function on UtxoEntry in place of
ConvertUtxosToMinimalOutputs
- Always decompress data loaded from the database now that a utxo entry
only consists of a specific output
- Introduce upgrade code to migrate the utxo set and spend journal to
the new format
- Update current database version to 9
- Update current utxo set version to 3
- Update current spend journal version to 3
- Introduce the ability to run upgrades after the block index has been
loaded
- Update all tests to expect the correct encodings, remove tests that no
longer apply, and add new ones for the new expected behavior
- Convert old tests for the legacy utxo format deserialization code to
test the new function that is used during upgrade
- Introduce a few new functions on UtxoViewpoint
- AddTxOut for adding an individual txout versus all of them
- addTxOut to handle the common code between the new AddTxOut and
existing AddTxOuts
- RemoveEntry for removing an individual txout
- Remove the ErrDiscordantTxTree error
- Since utxos are now retrieved using an outpoint, which includes the
tree, it is no longer possible to hit this error path