df1898cead
This modifies the way the unspent transaction output set is handled to
reverse its current semantics so that it is optimized for the typical
case, provides simpler handling, and resolves various issues with the
previous approach. In addition, it updates the transaction, address,
and existsaddress indexes to no longer remove entries from blocks that
have been disapproved as, in all cases, the data still exists in the
blockchain and thus should be queryable via the indexes even though
there is special handling applied which treats them as if they did not
exist in certain regards.
Prior to this change, transactions in the regular tree were not applied
to the utxo set until the next block was processed and did not vote
against them. However, that approach has several undesirable
consequences such as temporarily "invisible" utxos that are actually
spendable, disapproved transactions missing from indexes even though
they are still in the blockchain, and poor performance characteristics.
In a certain sense, the previous approach could be viewed as the
transactions not being valid until they were approved, however, that is
not really true because it was (and still is) perfectly acceptable to
spend utxos created by transactions in the regular tree of the same
block so long as they come before the transactions that spend them.
Further, utxos from a transaction in the regular tree of a block can be
spent in the next block so long as that block does not disapprove them,
which further illustrates that the utxos are actually valid unless they
are disapproved.
Consequently, this modifies that behavior to instead make the utxo set
always track the most recent block and remove the regular transactions
in the parent when a block votes against them. This approach is
significantly more efficient for the normal case where the previous
block is not disapproved by its successor.
Also, the terminology is changed in several places to refer to
disapproved blocks and transaction trees as opposed to invalid, because
invalid implies the tree/block is malformed or does not follow the
consensus rules. On the contrary, when a block votes against its
parent, it is only voting against regular transaction tree of the
parent. Both the block and transaction tree are still valid in that
case, only the regular transaction tree is treated as if it never
existed in terms of effects on the utxo set and duplicate transaction
semantics.
High level overview of changes:
- Modify the utxo viewpoint to reverse semantics as previously described
- Remove all code related to stake viewpoints
- Change all block connection code in the viewpoint to first undo all
transactions in the regular tree of the parent block if the current
one disapproves it then connect all of the stake txns followed by
the regular transactions in the block
- NOTE: The order here is important since stake transactions are not
allowed to spend outputs from the regular transactions in the same
block as the next block might disapprove them
- Change all block disconnection code in the viewpoint to first undo
all the transactions in the regular and stake trees of the block
being disconnected, and then resurrect the regular transactions in
the parent block if the block being disconnected disapproved of it
- Introduce a new type named viewFilteredSet for handling sets
filtered by transactions that already exist in a view
- Introduce a function on the viewpoint for specifically fetching the
inputs to the regular transactions
- Update mempool block connection and disconnection code to match the
new semantics
- Update all tests to handle the new semantics
- Modify the best state number of transactions to include all
transactions in all blocks regardless of disapproval because they
still had to be processed and still exist in the blockchain
- Remove include recent block parameter from mempool.FetchTransaction
since the utxoset now always includes the latest block
- This also has the side effect of correcting some unexpected results
such as coinbases in the most recent block being incorrectly
reported as having zero confirmations
- Modify mempool utxo fetch logic to use a cached disapproved view, when
needed, rather than recreating the view for every new transaction
added to it
- Update spend journal to include all transactions in the block instead
of only stake transactions from the current block and regular
transactions from the parent block
- Modify tx and address indexes to store the block index of each tx
along with its location within the files and update the query
functions to return the information as well
- Change the tx, address, and existsaddress indexes to index all
transactions regardless of their disapproval
- This also corrects several issues such as the inability to query and
retrieve transactions that exist in a disapproved block
- Update all RPC commands that return verbose transaction information
to set that newly available block index information properly
- Rename IsRegTxTreeKnownDisapproved in the mining.TxSource interface to
IsRegTxTreeKnownDisapproved
- NOTE: This will require a major bump to the mining module before
the next release
- Rename several utxoView instances to view for consistency
- Rename several variables that dealt with disapproved trees from
names that contained Invalid to ones that contain Disapproved
NOTE: This does not yet have database migration code and thus will
require a full chain download. It will exit with error in the case you
attempt to run it against an existing v4 database. The new database it
creates will be v5, so attempting to run an older version will reject
the new database to prevent corruption.
The database migration will be added in a separate commit.
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|---|---|---|
| .. | ||
| doc.go | ||
| error.go | ||
| go.mod | ||
| go.sum | ||
| log.go | ||
| mempool_test.go | ||
| mempool.go | ||
| policy_test.go | ||
| policy.go | ||
| README.md | ||
mempool
Package mempool provides a policy-enforced pool of unmined Decred transactions.
A key responsibility of the Decred network is mining transactions – regular transactions and stake 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.
The Policy configuration options has flags that control whether or not "standard" transactions and old votes are accepted into the mempool. 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 to be a "standard" transaction changes over time as policy and consensus rules evolve. 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 Decred 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 Decred 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
- Stake transaction support (ticket purchases, votes and revocations)
- Option to accept or reject old votes
- 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/decred/dcrd/mempool
License
Package mempool is licensed under the copyfree ISC License.