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
This commit implements the new “weight” metric introduced as part of
the segwit soft-fork. Post-fork activation, rather than limiting the
size of blocks and transactions based purely on serialized size, a new
metric “weight” will instead be used as a way to more accurately
reflect the costs of a tx/block on the system. With blocks constrained
by weight, the maximum block-size increases to ~4MB.
The current max orphan transaction size causes problems with dependent
transaction relay due to its artificially small size in relation to the
max standard transaction size.
Consequently, this modifies the orphan transaction policy by increasing
the max size of each orphan to the same value allowed for standard
non-orphan transactions and reducing the default max allowed number of
orphans to 100.
From a memory usage standpoint, the worst case max mem usage prior to
this change was 5MB plus structure and tracking overhead (1000 max
orphans * 5KB max each). With this, that is raised to 10MB (100 max
orphans * 100KB max each) in the worst case.
It is important to note that the values were originally implemented as a
naive means to control the size of the orphan pool before several of the
recent enhancements which more aggressively remove orphans from the
orphan pool were added, so they needed to be evaluated again.
For a very long time prior to recent changes, the orphan pool would
quickly reach the max allowed worst-case usage and effectively stay
there forever whereas with more recent changes, the actual run-time
orphan pool usage is usually much smaller.
Finally, as another point in favor of this change, as the network has
evolved, nodes have generally become better about orphan management and
as such missing ancestors will typically either be broadcast or mined
fairly quickly resulting in fewer overall orphans.
This commit adds a new option to the mempool’s policy configuration
which determines which transaction versions should be accepted as
standard.
The default version set by the policy within the server is 2; this
allows accepting transactions which have version 2 enabled in order to
utilize the new sequence locks feature.
This moves the priority-related code from the mempool package to the
mining package and also exports a new constant named UnminedHeight which
takes the place of the old unexported mempoolHeight.
Even though the mempool makes use of the priority code to make decisions
about what it will accept, priority really has to do with mining since
it influences which transactions will end up into a block. This change
also has the side effect of being a step towards enabling separation of
the mining code into its own package which, as previously mentioned,
needs access to the priority calculation code as well.
Finally, the mempoolHeight variable was poorly named since what it
really represents is a transaction that has not been mined into a block
yet. Renaming the variable to more accurately reflect its purpose makes
it clear that it belongs in the mining package which also needs the
definition now as well since the priority calculation code relies on it.
This will also benefit an outstanding PR which needs access to the same
value.
This coincides with the mempool only, policy change which enforces
transaction finality according to the median-time-past rather than
blockheader timestamps. The behavior is pre-cursor to full blown BIP
113 consensus deployment, and subsequent activation.
As a result, the TimeSource field in the mempoolConfig is no longer
needed so it has been removed. Additionally, checkTransactionStandard has been
modified to instead take a time.Time as the mempool is no longer explicitly
dependant on a Chain instance.
This changes the transaction input standardness checks as follows:
- Allow any script in a pay-to-script-hash transaction to be relayed and
mined so long as it has no more than 15 signature operations
- Remove the obsolete checks which naively calculated the number of
expected inputs in favor of the more accurate ScriptVerifyCleanStack
and ScriptVerifySigPushOnly functionality of the script engine that was
added after these checks.
This does the minimum work necessary to refactor the mempool code into
its own package. The idea is that separating this code into its own
package will greatly improve its testability, allow independent
benchmarking and profiling, and open up some interesting opportunities
for future development related to the memory pool.
There are likely some areas related to policy that could be further
refactored, however it is better to do that in future commits in order
to keep the changeset as small as possible during this refactor.
Overview of the major changes:
- Create the new package
- Move several files into the new package:
- mempool.go -> mempool/mempool.go
- mempoolerror.go -> mempool/error.go
- policy.go -> mempool/policy.go
- policy_test.go -> mempool/policy_test.go
- Update mempool logging to use the new mempool package logger
- Rename mempoolPolicy to Policy (so it's now mempool.Policy)
- Rename mempoolConfig to Config (so it's now mempool.Config)
- Rename mempoolTxDesc to TxDesc (so it's now mempool.TxDesc)
- Rename txMemPool to TxPool (so it's now mempool.TxPool)
- Move defaultBlockPrioritySize to the new package and export it
- Export DefaultMinRelayTxFee from the mempool package
- Export the CalcPriority function from the mempool package
- Introduce a new RawMempoolVerbose function on the TxPool and update
the RPC server to use it
- Update all references to the mempool to use the package.
- Add a skeleton README.md
