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1 : : // Copyright (c) The Bitcoin Core developers
2 : : // Distributed under the MIT software license, see the accompanying
3 : : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
4 : :
5 : : #include <compare>
6 : : #include <cstdint>
7 : : #include <functional>
8 : : #include <memory>
9 : : #include <optional>
10 : : #include <utility>
11 : : #include <vector>
12 : :
13 : : #include <util/feefrac.h>
14 : :
15 : : #ifndef BITCOIN_TXGRAPH_H
16 : : #define BITCOIN_TXGRAPH_H
17 : :
18 : : static constexpr unsigned MAX_CLUSTER_COUNT_LIMIT{64};
19 : :
20 : : /** Data structure to encapsulate fees, sizes, and dependencies for a set of transactions.
21 : : *
22 : : * Each TxGraph represents one or two such graphs ("main", and optionally "staging"), to allow for
23 : : * working with batches of changes that may still be discarded.
24 : : *
25 : : * The connected components within each transaction graph are called clusters: whenever one
26 : : * transaction is reachable from another, through any sequence of is-parent-of or is-child-of
27 : : * relations, they belong to the same cluster (so clusters include parents, children, but also
28 : : * grandparents, siblings, cousins twice removed, ...).
29 : : *
30 : : * For each graph, TxGraph implicitly defines an associated total ordering on its transactions
31 : : * (its linearization) that respects topology (parents go before their children), aiming for it to
32 : : * be close to the optimal order those transactions should be mined in if the goal is fee
33 : : * maximization, though this is a best effort only, not a strong guarantee.
34 : : *
35 : : * For more explanation, see https://delvingbitcoin.org/t/introduction-to-cluster-linearization/1032
36 : : *
37 : : * This linearization is partitioned into chunks: groups of transactions that according to this
38 : : * order would be mined together. Each chunk consists of the highest-feerate prefix of what remains
39 : : * of the linearization after removing previous chunks. TxGraph guarantees that the maintained
40 : : * linearization always results in chunks consisting of transactions that are connected. A chunk's
41 : : * transactions always belong to the same cluster.
42 : : *
43 : : * The interface is designed to accommodate an implementation that only stores the transitive
44 : : * closure of dependencies, so if B spends C, it does not distinguish between "A spending B" and
45 : : * "A spending both B and C".
46 : : */
47 : 203 : class TxGraph
48 : : {
49 : : public:
50 : : /** Internal identifier for a transaction within a TxGraph. */
51 : : using GraphIndex = uint32_t;
52 : :
53 : : /** Data type used to reference transactions within a TxGraph.
54 : : *
55 : : * Every transaction within a TxGraph has exactly one corresponding TxGraph::Ref, held by users
56 : : * of the class. Destroying the TxGraph::Ref removes the corresponding transaction (in both the
57 : : * main and staging graphs).
58 : : *
59 : : * Users of the class can inherit from TxGraph::Ref. If all Refs are inherited this way, the
60 : : * Ref* pointers returned by TxGraph functions can be cast to, and used as, this inherited type.
61 : : */
62 : : class Ref;
63 : :
64 : : enum class Level {
65 : : TOP, //!< Refers to staging if it exists, main otherwise.
66 : : MAIN //!< Always refers to the main graph, whether staging is present or not.
67 : : };
68 : :
69 : : /** Virtual destructor, so inheriting is safe. */
70 : 203 : virtual ~TxGraph() = default;
71 : : /** Initialize arg (which must be an empty Ref) to refer to a new transaction in this graph
72 : : * with the specified feerate.
73 : : *
74 : : * If a staging graph exists, the new transaction is only created there. feerate.size must be
75 : : * strictly positive. In all further calls, only Refs passed to AddTransaction() are allowed
76 : : * to be passed to this TxGraph object (or empty Ref objects). Ref objects may outlive the
77 : : * TxGraph they were added to. */
78 : : virtual void AddTransaction(Ref& arg, const FeePerWeight& feerate) noexcept = 0;
79 : : /** Remove the specified transaction. If a staging graph exists, the removal only happens
80 : : * there. This is a no-op if the transaction was already removed.
81 : : *
82 : : * TxGraph may internally reorder transaction removals with dependency additions for
83 : : * performance reasons. If together with any transaction removal all its descendants, or all
84 : : * its ancestors, are removed as well (which is what always happens in realistic scenarios),
85 : : * this reordering will not affect the behavior of TxGraph.
86 : : *
87 : : * As an example, imagine 3 transactions A,B,C where B depends on A. If a dependency of C on B
88 : : * is added, and then B is deleted, C will still depend on A. If the deletion of B is reordered
89 : : * before the C->B dependency is added, the dependency adding has no effect. If, together with
90 : : * the deletion of B also either A or C is deleted, there is no distinction between the
91 : : * original order case and the reordered case.
92 : : */
93 : : virtual void RemoveTransaction(const Ref& arg) noexcept = 0;
94 : : /** Add a dependency between two specified transactions. If a staging graph exists, the
95 : : * dependency is only added there. Parent may not be a descendant of child already (but may
96 : : * be an ancestor of it already, in which case this is a no-op). If either transaction is
97 : : * already removed, this is a no-op. */
98 : : virtual void AddDependency(const Ref& parent, const Ref& child) noexcept = 0;
99 : : /** Modify the fee of the specified transaction, in both the main graph and the staging
100 : : * graph if it exists. Wherever the transaction does not exist (or was removed), this has no
101 : : * effect. */
102 : : virtual void SetTransactionFee(const Ref& arg, int64_t fee) noexcept = 0;
103 : :
104 : : /** TxGraph is internally lazy, and will not compute many things until they are needed.
105 : : * Calling DoWork will perform some work now (controlled by iters) so that future operations
106 : : * are fast, if there is any. Returns whether all currently-available work is done. This can
107 : : * be invoked while oversized, but oversized graphs will be skipped by this call. */
108 : : virtual bool DoWork(uint64_t iters) noexcept = 0;
109 : :
110 : : /** Create a staging graph (which cannot exist already). This acts as if a full copy of
111 : : * the transaction graph is made, upon which further modifications are made. This copy can
112 : : * be inspected, and then either discarded, or the main graph can be replaced by it by
113 : : * committing it. */
114 : : virtual void StartStaging() noexcept = 0;
115 : : /** Discard the existing active staging graph (which must exist). */
116 : : virtual void AbortStaging() noexcept = 0;
117 : : /** Replace the main graph with the staging graph (which must exist). */
118 : : virtual void CommitStaging() noexcept = 0;
119 : : /** Check whether a staging graph exists. */
120 : : virtual bool HaveStaging() const noexcept = 0;
121 : :
122 : : /** Determine whether the graph is oversized (contains a connected component of more than the
123 : : * configured maximum cluster count). Some of the functions below are not available
124 : : * for oversized graphs. The mutators above are always available. Removing a transaction by
125 : : * destroying its Ref while staging exists will not clear main's oversizedness until staging
126 : : * is aborted or committed. */
127 : : virtual bool IsOversized(Level level) noexcept = 0;
128 : : /** Determine whether arg exists in the graph (i.e., was not removed). This is
129 : : * available even for oversized graphs. */
130 : : virtual bool Exists(const Ref& arg, Level level) noexcept = 0;
131 : : /** Get the individual transaction feerate of transaction arg. Returns the empty FeePerWeight
132 : : * if arg does not exist in either main or staging. This is available even for oversized
133 : : * graphs. */
134 : : virtual FeePerWeight GetIndividualFeerate(const Ref& arg) noexcept = 0;
135 : : /** Get the feerate of the chunk which transaction arg is in, in the main graph. Returns the
136 : : * empty FeePerWeight if arg does not exist in the main graph. The main graph must not be
137 : : * oversized. */
138 : : virtual FeePerWeight GetMainChunkFeerate(const Ref& arg) noexcept = 0;
139 : : /** Get pointers to all transactions in the cluster which arg is in. The transactions are
140 : : * returned in graph order. The queried graph must not be oversized. Returns {} if
141 : : * arg does not exist in the queried graph. */
142 : : virtual std::vector<Ref*> GetCluster(const Ref& arg, Level level) noexcept = 0;
143 : : /** Get pointers to all ancestors of the specified transaction (including the transaction
144 : : * itself), in unspecified order. The queried graph must not be oversized.
145 : : * Returns {} if arg does not exist in the graph. */
146 : : virtual std::vector<Ref*> GetAncestors(const Ref& arg, Level level) noexcept = 0;
147 : : /** Get pointers to all descendants of the specified transaction (including the transaction
148 : : * itself), in unspecified order. The queried graph must not be oversized.
149 : : * Returns {} if arg does not exist in the graph. */
150 : : virtual std::vector<Ref*> GetDescendants(const Ref& arg, Level level) noexcept = 0;
151 : : /** Like GetAncestors, but return the Refs for all transactions in the union of the provided
152 : : * arguments' ancestors (each transaction is only reported once). Refs that do not exist in
153 : : * the queried graph are ignored. Null refs are not allowed. */
154 : : virtual std::vector<Ref*> GetAncestorsUnion(std::span<const Ref* const> args, Level level) noexcept = 0;
155 : : /** Like GetDescendants, but return the Refs for all transactions in the union of the provided
156 : : * arguments' descendants (each transaction is only reported once). Refs that do not exist in
157 : : * the queried graph are ignored. Null refs are not allowed. */
158 : : virtual std::vector<Ref*> GetDescendantsUnion(std::span<const Ref* const> args, Level level) noexcept = 0;
159 : : /** Get the total number of transactions in the graph. This is available even
160 : : * for oversized graphs. */
161 : : virtual GraphIndex GetTransactionCount(Level level) noexcept = 0;
162 : : /** Compare two transactions according to their order in the main graph. Both transactions must
163 : : * be in the main graph. The main graph must not be oversized. */
164 : : virtual std::strong_ordering CompareMainOrder(const Ref& a, const Ref& b) noexcept = 0;
165 : : /** Count the number of distinct clusters that the specified transactions belong to. Refs that
166 : : * do not exist in the queried graph are ignored. Refs can not be null. The queried graph must
167 : : * not be oversized. */
168 : : virtual GraphIndex CountDistinctClusters(std::span<const Ref* const>, Level level) noexcept = 0;
169 : : /** For both main and staging (which must both exist and not be oversized), return the combined
170 : : * respective feerate diagrams, including chunks from all clusters, but excluding clusters
171 : : * that appear identically in both. Use FeeFrac rather than FeePerWeight so CompareChunks is
172 : : * usable without type-conversion. */
173 : : virtual std::pair<std::vector<FeeFrac>, std::vector<FeeFrac>> GetMainStagingDiagrams() noexcept = 0;
174 : : /** Remove transactions (including their own descendants) according to a fast but best-effort
175 : : * strategy such that the TxGraph's cluster and size limits are respected. Applies to staging
176 : : * if it exists, and to main otherwise. Returns the list of all removed transactions in
177 : : * unspecified order. This has no effect unless the relevant graph is oversized. */
178 : : virtual std::vector<Ref*> Trim() noexcept = 0;
179 : :
180 : : /** Interface returned by GetBlockBuilder. */
181 : : class BlockBuilder
182 : : {
183 : : protected:
184 : : /** Make constructor non-public (use TxGraph::GetBlockBuilder()). */
185 : 9012 : BlockBuilder() noexcept = default;
186 : : public:
187 : : /** Support safe inheritance. */
188 : 9012 : virtual ~BlockBuilder() = default;
189 : : /** Get the chunk that is currently suggested to be included, plus its feerate, if any. */
190 : : virtual std::optional<std::pair<std::vector<Ref*>, FeePerWeight>> GetCurrentChunk() noexcept = 0;
191 : : /** Mark the current chunk as included, and progress to the next one. */
192 : : virtual void Include() noexcept = 0;
193 : : /** Mark the current chunk as skipped, and progress to the next one. Further chunks from
194 : : * the same cluster as the current one will not be reported anymore. */
195 : : virtual void Skip() noexcept = 0;
196 : : };
197 : :
198 : : /** Construct a block builder, drawing chunks in order, from the main graph, which cannot be
199 : : * oversized. While the returned object exists, no mutators on the main graph are allowed.
200 : : * The BlockBuilder object must not outlive the TxGraph it was created with. */
201 : : virtual std::unique_ptr<BlockBuilder> GetBlockBuilder() noexcept = 0;
202 : : /** Get the last chunk in the main graph, i.e., the last chunk that would be returned by a
203 : : * BlockBuilder created now, together with its feerate. The chunk is returned in
204 : : * reverse-topological order, so every element is preceded by all its descendants. The main
205 : : * graph must not be oversized. If the graph is empty, {{}, FeePerWeight{}} is returned. */
206 : : virtual std::pair<std::vector<Ref*>, FeePerWeight> GetWorstMainChunk() noexcept = 0;
207 : :
208 : : /** Get the approximate memory usage for this object, just counting the main graph. If a
209 : : * staging graph is present, return a number corresponding to memory usage after
210 : : * AbortStaging() would be called. BlockBuilders' memory usage, memory usage of internally
211 : : * queued operations, and memory due to temporary caches, is not included here. Can always be
212 : : * called. */
213 : : virtual size_t GetMainMemoryUsage() noexcept = 0;
214 : :
215 : : /** Perform an internal consistency check on this object. */
216 : : virtual void SanityCheck() const = 0;
217 : :
218 : : protected:
219 : : // Allow TxGraph::Ref to call UpdateRef and UnlinkRef.
220 : : friend class TxGraph::Ref;
221 : : /** Inform the TxGraph implementation that a TxGraph::Ref has moved. */
222 : : virtual void UpdateRef(GraphIndex index, Ref& new_location) noexcept = 0;
223 : : /** Inform the TxGraph implementation that a TxGraph::Ref was destroyed. */
224 : : virtual void UnlinkRef(GraphIndex index) noexcept = 0;
225 : : // Allow TxGraph implementations (inheriting from it) to access Ref internals.
226 : 64011 : static TxGraph*& GetRefGraph(Ref& arg) noexcept { return arg.m_graph; }
227 [ - + + - : 68171 : static TxGraph* GetRefGraph(const Ref& arg) noexcept { return arg.m_graph; }
- + - + -
+ - + - -
- + - + +
- + - + -
+ - ]
228 : : static GraphIndex& GetRefIndex(Ref& arg) noexcept { return arg.m_index; }
229 [ + - - + : 76357 : static GraphIndex GetRefIndex(const Ref& arg) noexcept { return arg.m_index; }
- + - + -
+ - - - +
+ + + - +
- ]
230 : :
231 : : public:
232 : : class Ref
233 : : {
234 : : // Allow TxGraph's GetRefGraph and GetRefIndex to access internals.
235 : : friend class TxGraph;
236 : : /** Which Graph the Entry lives in. nullptr if this Ref is empty. */
237 : : TxGraph* m_graph = nullptr;
238 : : /** Index into the Graph's m_entries. Only used if m_graph != nullptr. */
239 : : GraphIndex m_index = GraphIndex(-1);
240 : : public:
241 : : /** Construct an empty Ref. It can be initialized through TxGraph::AddTransaction. */
242 [ + - ]: 117651 : Ref() noexcept = default;
243 : : /** Destroy this Ref. If it is not empty, the corresponding transaction is removed (in both
244 : : * main and staging, if it exists). */
245 : : virtual ~Ref();
246 : : // Support move-constructing a Ref.
247 : : Ref& operator=(Ref&& other) noexcept = delete;
248 : : Ref(Ref&& other) noexcept;
249 : : // Do not permit copy constructing or copy assignment. A TxGraph entry can have at most one
250 : : // Ref pointing to it.
251 : : Ref& operator=(const Ref&) = delete;
252 : : Ref(const Ref&) = delete;
253 : : };
254 : : };
255 : :
256 : : /** Construct a new TxGraph with the specified limit on the number of transactions within a cluster,
257 : : * and on the sum of transaction sizes within a cluster.
258 : : *
259 : : * - max_cluster_count cannot exceed MAX_CLUSTER_COUNT_LIMIT.
260 : : * - acceptable_iters controls how many linearization optimization steps will be performed per
261 : : * cluster before they are considered to be of acceptable quality.
262 : : * - fallback_order determines how to break tie-breaks between transactions:
263 : : * fallback_order(a, b) < 0 means a is "better" than b, and will (in case of ties) be placed
264 : : * first. This ordering must be stable over the transactions' lifetimes.
265 : : */
266 : : std::unique_ptr<TxGraph> MakeTxGraph(
267 : : unsigned max_cluster_count,
268 : : uint64_t max_cluster_size,
269 : : uint64_t acceptable_iters,
270 : : const std::function<std::strong_ordering(const TxGraph::Ref&, const TxGraph::Ref&)>& fallback_order
271 : : ) noexcept;
272 : :
273 : : #endif // BITCOIN_TXGRAPH_H
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