a59ac5b18f
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. This was inspired by similar recent
changes in Bitcoin Core.
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 such as whether the containing transaction is a coinbase and the
block height it was a part of are duplicated 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 isn't actually used anywhere aside
from the gettxout RPC where it also isn't used by anything important
either. Consequently, this also removes the version field of the
gettxout RPC result.
The utxos 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 the tests for the new format and adds a new
function to the tests to convert the old test data to the new format for
convenience. The data has already been converted and updated in the
commit.
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
- Modify the spend journal serialization format
- The old version field is now reserved and always stores zero and
ignores it when reading
- This allows old entries to be used by new code without having to
migrate the entire spend journal
- Remove version field from gettxout RPC result
- Convert UtxoEntry to represent a specific utxo instead of a
transaction with all remaining utxos
- Optimize for memory usage with an eye towards a utxo cache
- Combine details such as whether the txout was contained in a
coinbase, is spent, and is modified into a single packed field of
bit flags
- 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 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 block height and coinbase
information with every spent txout
- Introduce code to handle fetching the missing information from
another utxo from the same transaction in the event an old style
entry is encountered
- Make use of a database cursor with seek to do this much more
efficiently than testing every possible output
- 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 to the new format
- Store versions of the utxoset and spend journal buckets
- Allow migration process to be interrupted and resumed
- 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
- Update the utxostore test data and add function that was used to
convert it
- 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
- fetchEntryByHash for fetching any remaining utxo for a given
transaction hash
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|---|---|---|
| .. | ||
| doc.go | ||
| error.go | ||
| estimatefee.go | ||
| estimatefee_test.go | ||
| log.go | ||
| mempool.go | ||
| mempool_test.go | ||
| policy.go | ||
| policy_test.go | ||
| README.md | ||
mempool
Package mempool provides a policy-enforced pool of unmined bitcoin transactions.
A key responsbility of the bitcoin network is mining user-generated transactions into blocks. In order to facilitate this, the mining process relies on having a readily-available source of transactions to include in a block that is being solved.
At a high level, this package satisfies that requirement by providing an in-memory pool of fully validated transactions that can also optionally be further filtered based upon a configurable policy.
One of the policy configuration options controls whether or not "standard" transactions are accepted. In essence, a "standard" transaction is one that satisfies a fairly strict set of requirements that are largely intended to help provide fair use of the system to all users. It is important to note that what is considered a "standard" transaction changes over time. For some insight, at the time of this writing, an example of some of the criteria that are required for a transaction to be considered standard are that it is of the most-recently supported version, finalized, does not exceed a specific size, and only consists of specific script forms.
Since this package does not deal with other bitcoin specifics such as network communication and transaction relay, it returns a list of transactions that were accepted which gives the caller a high level of flexibility in how they want to proceed. Typically, this will involve things such as relaying the transactions to other peers on the network and notifying the mining process that new transactions are available.
This package has intentionally been designed so it can be used as a standalone package for any projects needing the ability create an in-memory pool of bitcoin transactions that are not only valid by consensus rules, but also adhere to a configurable policy.
Feature Overview
The following is a quick overview of the major features. It is not intended to be an exhaustive list.
- Maintain a pool of fully validated transactions
- Reject non-fully-spent duplicate transactions
- Reject coinbase transactions
- Reject double spends (both from the chain and other transactions in pool)
- Reject invalid transactions according to the network consensus rules
- Full script execution and validation with signature cache support
- Individual transaction query support
- Orphan transaction support (transactions that spend from unknown outputs)
- Configurable limits (see transaction acceptance policy)
- Automatic addition of orphan transactions that are no longer orphans as new transactions are added to the pool
- Individual orphan transaction query support
- Configurable transaction acceptance policy
- Option to accept or reject standard transactions
- Option to accept or reject transactions based on priority calculations
- Rate limiting of low-fee and free transactions
- Non-zero fee threshold
- Max signature operations per transaction
- Max orphan transaction size
- Max number of orphan transactions allowed
- Additional metadata tracking for each transaction
- Timestamp when the transaction was added to the pool
- Most recent block height when the transaction was added to the pool
- The fee the transaction pays
- The starting priority for the transaction
- Manual control of transaction removal
- Recursive removal of all dependent transactions
Installation and Updating
$ go get -u github.com/btcsuite/btcd/mempool
License
Package mempool is licensed under the copyfree ISC License.