Control mempool persistence using a command line parameter.

Mempool persistence was added in
3f78562df5, 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.

src/init.cpp

@@ -206,8 +206,9 @@ void Shutdown()
 
     StopTorControl();
     UnregisterNodeSignals(GetNodeSignals());
-    if (fDumpMempoolLater)
+    if (fDumpMempoolLater && GetArg("-persistmempool", DEFAULT_PERSIST_MEMPOOL)) {
         DumpMempool();
+    }
 
     if (fFeeEstimatesInitialized)
     {
@@ -339,6 +340,7 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += HelpMessageOpt("-maxorphantx=<n>", strprintf(_("Keep at most <n> unconnectable transactions in memory (default: %u)"), DEFAULT_MAX_ORPHAN_TRANSACTIONS));
     strUsage += HelpMessageOpt("-maxmempool=<n>", strprintf(_("Keep the transaction memory pool below <n> megabytes (default: %u)"), DEFAULT_MAX_MEMPOOL_SIZE));
     strUsage += HelpMessageOpt("-mempoolexpiry=<n>", 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 reconstructions (default: %u)"), DEFAULT_BLOCK_RECONSTRUCTION_EXTRA_TXN));
     strUsage += HelpMessageOpt("-par=<n>", strprintf(_("Set the number of script verification threads (%u to %d, 0 = auto, <0 = leave that many cores free, default: %d)"),
         -GetNumCores(), MAX_SCRIPTCHECK_THREADS, DEFAULT_SCRIPTCHECK_THREADS));
@@ -666,8 +668,10 @@ void ThreadImport(std::vector<boost::filesystem::path> vImportFiles)
         StartShutdown();
     }
     } // End scope of CImportingNow
-    LoadMempool();
+    if (GetArg("-persistmempool", DEFAULT_PERSIST_MEMPOOL)) {
-    fDumpMempoolLater = !fRequestShutdown;
+        LoadMempool();
+        fDumpMempoolLater = !fRequestShutdown;
+    }
 }
 
 /** Sanity checks

src/validation.h

@@ -131,7 +131,8 @@ static const bool DEFAULT_PERMIT_BAREMULTISIG = true;
 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 -mempoolreplacement */
 static const bool DEFAULT_ENABLE_REPLACEMENT = true;
 /** Default for using fee filter */