init: auto-size dbcache to available system RAM

src/init.cpp

@@ -508,7 +508,7 @@ void SetupServerArgs(ArgsManager& argsman, bool can_listen_ipc)
     argsman.AddArg("-corepolicy", strprintf("Use Bitcoin Core policy defaults (default: %u)", DEFAULT_COREPOLICY), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-datadir=<dir>", "Specify data directory", ArgsManager::ALLOW_ANY | ArgsManager::DISALLOW_NEGATION, OptionsCategory::OPTIONS);
     argsman.AddArg("-dbbatchsize", strprintf("Maximum database write batch size in bytes (default: %u)", nDefaultDbBatchSize), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::OPTIONS);
-    argsman.AddArg("-dbcache=<n>", strprintf("Maximum database cache size <n> MiB (minimum %d, default: %d). Make sure you have enough RAM. In addition, unused memory allocated to the mempool is shared with this cache (see -maxmempool).", MIN_DB_CACHE >> 20, DEFAULT_DB_CACHE >> 20), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
+    argsman.AddArg("-dbcache=<n>", strprintf("Maximum database cache size <n> MiB (minimum %d, default: half of system RAM up to 16384 MiB, or %d MiB if detection fails). In addition, unused memory allocated to the mempool is shared with this cache (see -maxmempool).", MIN_DB_CACHE >> 20, DEFAULT_DB_CACHE >> 20), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-dbfilesize",
                    strprintf("Target size of files within databases, in MiB (%u to %u, default: %u).",
                              1, 1024,

src/node/caches.cpp

@@ -9,6 +9,7 @@
 #include <kernel/caches.h>
 #include <logging.h>
 #include <util/byte_units.h>
+#include <util/mempressure.h>
 
 #include <algorithm>
 #include <string>
@@ -32,6 +33,13 @@ CacheSizes CalculateCacheSizes(const ArgsManager& args, size_t n_indexes)
         uint64_t db_cache_bytes = SaturatingLeftShift<uint64_t>(*db_cache, 20);
         constexpr auto max_db_cache{sizeof(void*) == 4 ? MAX_32BIT_DBCACHE : std::numeric_limits<size_t>::max()};
         total_cache = std::max<size_t>(MIN_DB_CACHE, std::min<uint64_t>(db_cache_bytes, max_db_cache));
+    } else {
+        uint64_t total_mem = GetTotalSystemMemory();
+        if (total_mem > 0) {
+            constexpr uint64_t max_auto_cache{sizeof(void*) == 4 ? MAX_32BIT_DBCACHE : uint64_t{16} * 1024 * 1024 * 1024};
+            uint64_t auto_cache = std::min(total_mem / 2, max_auto_cache);
+            total_cache = std::max<size_t>(MIN_DB_CACHE, static_cast<size_t>(auto_cache));
+        }
     }
 
     IndexCacheSizes index_sizes;

src/qt/optionsmodel.cpp

@@ -28,6 +28,7 @@
 #include <node/mempool_args.h> // for ParseDustDynamicOpt
 #include <outputtype.h>
 #include <policy/settings.h>
+#include <util/mempressure.h>
 #include <util/moneystr.h> // for FormatMoney
 #include <util/string.h>
 #include <validation.h>    // For DEFAULT_SCRIPTCHECK_THREADS
@@ -37,7 +38,9 @@
 #include <interfaces/wallet.h>
 #endif
 
+#include <algorithm>
 #include <chrono>
+#include <limits>
 #include <string>
 #include <unordered_set>
 #include <utility>
@@ -694,7 +697,12 @@ QVariant OptionsModel::getOption(OptionID option, const std::string& suffix) con
                suffix.empty()          ? getOption(option, "-prev") :
                                          DEFAULT_PRUNE_TARGET_MiB;
     case DatabaseCache:
-        return qlonglong(SettingToInt(setting(), DEFAULT_DB_CACHE >> 20));
+    {
+        uint64_t total_mem = GetTotalSystemMemory();
+        constexpr uint64_t max_auto_cache{sizeof(void*) == 4 ? uint64_t{1024} : uint64_t{16} * 1024};
+        int default_mib = total_mem > 0 ? static_cast<int>(std::min(total_mem / 2 >> 20, max_auto_cache)) : static_cast<int>(DEFAULT_DB_CACHE >> 20);
+        return qlonglong(SettingToInt(setting(), default_mib));
+    }
     case ThreadsScriptVerif:
         return qlonglong(SettingToInt(setting(), DEFAULT_SCRIPTCHECK_THREADS));
     case Listen:

src/util/mempressure.cpp

@@ -12,14 +12,17 @@
 #ifdef HAVE_LINUX_SYSINFO
 #include <sys/sysinfo.h>
 #endif
+#ifdef __APPLE__
+#include <sys/sysctl.h>
+#endif
 #ifdef WIN32
 #include <windows.h>
 #endif
 
 #include <cstddef>
 #include <cstdint>
 
-size_t g_low_memory_threshold{0};
+size_t g_low_memory_threshold{256_MiB};
 
 bool SystemNeedsMemoryReleased()
 {
@@ -54,3 +57,28 @@ bool SystemNeedsMemoryReleased()
     // NOTE: sysconf(_SC_AVPHYS_PAGES) doesn't account for caches on at least Linux, so not safe to use here
     return false;
 }
+
+uint64_t GetTotalSystemMemory()
+{
+#ifdef WIN32
+    MEMORYSTATUSEX mem_status;
+    mem_status.dwLength = sizeof(mem_status);
+    if (GlobalMemoryStatusEx(&mem_status)) {
+        return mem_status.ullTotalPhys;
+    }
+#endif
+#ifdef HAVE_LINUX_SYSINFO
+    struct sysinfo sys_info;
+    if (!sysinfo(&sys_info)) {
+        return uint64_t(sys_info.totalram) * sys_info.mem_unit;
+    }
+#endif
+#ifdef __APPLE__
+    int64_t memsize = 0;
+    size_t len = sizeof(memsize);
+    if (!sysctlbyname("hw.memsize", &memsize, &len, nullptr, 0) && memsize > 0) {
+        return static_cast<uint64_t>(memsize);
+    }
+#endif
+    return 0;
+}

src/util/mempressure.h

@@ -6,9 +6,11 @@
 #define BITCOIN_UTIL_MEMPRESSURE_H
 
 #include <cstddef>
+#include <cstdint>
 
 extern size_t g_low_memory_threshold;
 
 bool SystemNeedsMemoryReleased();
+uint64_t GetTotalSystemMemory();
 
 #endif // BITCOIN_UTIL_MEMPRESSURE_H