Control mempool persistence using a command line parameter.

Summary:
Mempool persistence was added in
3f78562, and is always on. This commit
introduces a command-line parameter -persistmempool, which defaults to
true. When set to false:
- mempool.dat is not loaded when the node starts.
- mempool.dat is not written when the node stops.

Backport core's PR9966 and PR10342

Test Plan:
  make check
  ./test/functional/test_runner.py mempool_persist.py

Reviewers: #bitcoin_abc, dagurval

Reviewed By: #bitcoin_abc, dagurval

Differential Revision: https://reviews.bitcoinabc.org/D964

src/init.cpp

@@ -203,7 +203,10 @@ void Shutdown() {
 
     StopTorControl();
     UnregisterNodeSignals(GetNodeSignals());
-    if (fDumpMempoolLater) DumpMempool();
+    if (fDumpMempoolLater &&
+        GetArg("-persistmempool", DEFAULT_PERSIST_MEMPOOL)) {
+        DumpMempool();
+    }
 
     if (fFeeEstimatesInitialized) {
         fs::path est_path = GetDataDir() / FEE_ESTIMATES_FILENAME;
@@ -372,6 +375,11 @@ std::string HelpMessage(HelpMessageMode mode) {
                        strprintf(_("Do not keep transactions in the mempool "
                                    "longer than <n> hours (default: %u)"),
                                  DEFAULT_MEMPOOL_EXPIRY));
+    strUsage +=
+        HelpMessageOpt("-persistmempool",
+                       strprintf(_("Whether to save the mempool on shutdown "
+                                   "and load on restart (default: %u)"),
+                                 DEFAULT_PERSIST_MEMPOOL));
     strUsage += HelpMessageOpt(
         "-blockreconstructionextratxn=<n>",
         strprintf(_("Extra transactions to keep in memory for compact block "
@@ -1043,8 +1051,10 @@ void ThreadImport(const Config &config, std::vector<fs::path> vImportFiles) {
             StartShutdown();
         }
     } // End scope of CImportingNow
-    LoadMempool(config);
-    fDumpMempoolLater = !fRequestShutdown;
+    if (GetArg("-persistmempool", DEFAULT_PERSIST_MEMPOOL)) {
+        LoadMempool(config);
+        fDumpMempoolLater = !fRequestShutdown;
+    }
 }
 
 /** Sanity checks

src/validation.h

@@ -152,6 +152,8 @@ static const bool DEFAULT_CHECKPOINTS_ENABLED = true;
 static const bool DEFAULT_TXINDEX = false;
 static const unsigned int DEFAULT_BANSCORE_THRESHOLD = 100;
 
+/** Default for -persistmempool */
+static const bool DEFAULT_PERSIST_MEMPOOL = true;
 /** Default for using fee filter */
 static const bool DEFAULT_FEEFILTER = true;
 

test/functional/mempool_persist.py

@@ -0,0 +1,98 @@
+#!/usr/bin/env python3
+# Copyright (c) 2014-2017 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Test mempool persistence.
+
+By default, bitcoind will dump mempool on shutdown and
+then reload it on startup. This can be overridden with
+the -persistmempool=0 command line option.
+
+Test is as follows:
+
+  - start node0, node1 and node2. node1 has -persistmempool=0
+  - create 5 transactions on node2 to its own address. Note that these
+    are not sent to node0 or node1 addresses because we don't want
+    them to be saved in the wallet.
+  - check that node0 and node1 have 5 transactions in their mempools
+  - shutdown all nodes.
+  - startup node0. Verify that it still has 5 transactions
+    in its mempool. Shutdown node0. This tests that by default the
+    mempool is persistent.
+  - startup node1. Verify that its mempool is empty. Shutdown node1.
+    This tests that with -persistmempool=0, the mempool is not
+    dumped to disk when the node is shut down.
+  - Restart node0 with -persistmempool=0. Verify that its mempool is
+    empty. Shutdown node0. This tests that with -persistmempool=0,
+    the mempool is not loaded from disk on start up.
+  - Restart node0 with -persistmempool. Verify that it has 5
+    transactions in its mempool. This tests that -persistmempool=0
+    does not overwrite a previously valid mempool stored on disk.
+
+"""
+import time
+
+from test_framework.mininode import wait_until
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import *
+
+
+class MempoolPersistTest(BitcoinTestFramework):
+
+    def __init__(self):
+        super().__init__()
+        # We need 3 nodes for this test. Node1 does not have a persistent mempool.
+        self.num_nodes = 3
+        self.setup_clean_chain = False
+        self.extra_args = [[], ["-persistmempool=0"], []]
+
+    def run_test(self):
+        chain_height = self.nodes[0].getblockcount()
+        assert_equal(chain_height, 200)
+
+        self.log.debug("Mine a single block to get out of IBD")
+        self.nodes[0].generate(1)
+        self.sync_all()
+
+        self.log.debug("Send 5 transactions from node2 (to its own address)")
+        for i in range(5):
+            self.nodes[2].sendtoaddress(
+                self.nodes[2].getnewaddress(), Decimal("10"))
+        self.sync_all()
+
+        self.log.debug(
+            "Verify that node0 and node1 have 5 transactions in their mempools")
+        assert_equal(len(self.nodes[0].getrawmempool()), 5)
+        assert_equal(len(self.nodes[1].getrawmempool()), 5)
+
+        self.log.debug(
+            "Stop-start node0 and node1. Verify that node0 has the transactions in its mempool and node1 does not.")
+        stop_nodes(self.nodes)
+        self.nodes = []
+        self.nodes.append(start_node(0, self.options.tmpdir))
+        self.nodes.append(start_node(1, self.options.tmpdir))
+        # Give bitcoind a second to reload the mempool
+        time.sleep(1)
+        assert wait_until(lambda: len(self.nodes[0].getrawmempool()) == 5)
+        assert_equal(len(self.nodes[1].getrawmempool()), 0)
+
+        self.log.debug(
+            "Stop-start node0 with -persistmempool=0. Verify that it doesn't load its mempool.dat file.")
+        stop_nodes(self.nodes)
+        self.nodes = []
+        self.nodes.append(start_node(
+            0, self.options.tmpdir, ["-persistmempool=0"]))
+        # Give bitcoind a second to reload the mempool
+        time.sleep(1)
+        assert_equal(len(self.nodes[0].getrawmempool()), 0)
+
+        self.log.debug(
+            "Stop-start node0. Verify that it has the transactions in its mempool.")
+        stop_nodes(self.nodes)
+        self.nodes = []
+        self.nodes.append(start_node(0, self.options.tmpdir))
+        assert wait_until(lambda: len(self.nodes[0].getrawmempool()) == 5)
+
+
+if __name__ == '__main__':
+    MempoolPersistTest().main()

test/functional/test_runner.py

@@ -68,6 +68,7 @@
     'rest.py',
     'mempool_spendcoinbase.py',
     'mempool_reorg.py',
+    'mempool_persist.py',
     'httpbasics.py',
     'multi_rpc.py',
     'proxy_test.py',