Merge bitcoin/bitcoin#28358: Drop -dbcache limit

bb3b980dfd validation: drop maximum -dbcache (Sjors Provoost)

Pull request description:

  Due to recent UTXO set growth, the current maximum value for `-dbcache` of 16GB is ~just months away from being~ insufficient (for those who wish to complete IBD with the UTXO set held in RAM).

  This drops the limit. It also adds a warning that it's up to users to check that they have enough RAM.

  Fixes #28249.

  ---

  A previous version of this PR increased the maximum to 64GB. It also made startup abort if the value provided is too high, rather than quietly round it down. But this didn't get much support.

ACKs for top commit:
  achow101:
    ACK bb3b980dfd
  tdb3:
    ACK bb3b980dfd
  BenWestgate:
    crACK bb3b980dfd.

Tree-SHA512: 8515fff468c2387a0b04bd9523ab1df46d6325738588b7550fabddbb8624817a583d95b95ea246407f9f0ff3e43e760cf7334621bec6af79710176328528a3ef

doc/release-notes-28358.md

@@ -0,0 +1,6 @@
+Updated settings
+------
+
+- The maximum allowed value for the `-dbcache` configuration option has been
+  dropped due to recent UTXO set growth. Note that before this change, large `-dbcache`
+  values were automatically reduced to 16 GiB (1 GiB on 32 bit systems). (#28358)

src/init.cpp

@@ -490,7 +490,7 @@ void SetupServerArgs(ArgsManager& argsman, bool can_listen_ipc)
     argsman.AddArg("-conf=<file>", strprintf("Specify path to read-only configuration file. Relative paths will be prefixed by datadir location (only useable from command line, not configuration file) (default: %s)", BITCOIN_CONF_FILENAME), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-datadir=<dir>", "Specify data directory", ArgsManager::ALLOW_ANY, 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 (%d to %d, default: %d). In addition, unused mempool memory is shared for this cache (see -maxmempool).", nMinDbCache, nMaxDbCache, nDefaultDbCache), ArgsManager::ALLOW_ANY, 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).", nMinDbCache, nDefaultDbCache), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-includeconf=<file>", "Specify additional configuration file, relative to the -datadir path (only useable from configuration file, not command line)", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-allowignoredconf", strprintf("For backwards compatibility, treat an unused %s file in the datadir as a warning, not an error.", BITCOIN_CONF_FILENAME), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-loadblock=<file>", "Imports blocks from external file on startup", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);

src/node/caches.cpp

@@ -13,7 +13,6 @@ CacheSizes CalculateCacheSizes(const ArgsManager& args, size_t n_indexes)
 {
     int64_t nTotalCache = (args.GetIntArg("-dbcache", nDefaultDbCache) << 20);
     nTotalCache = std::max(nTotalCache, nMinDbCache << 20); // total cache cannot be less than nMinDbCache
-    nTotalCache = std::min(nTotalCache, nMaxDbCache << 20); // total cache cannot be greater than nMaxDbcache
     CacheSizes sizes;
     sizes.block_tree_db = std::min(nTotalCache / 8, nMaxBlockDBCache << 20);
     nTotalCache -= sizes.block_tree_db;

src/qt/forms/optionsdialog.ui

@@ -105,7 +105,7 @@
          <item>
           <widget class="QLabel" name="databaseCacheLabel">
            <property name="toolTip">
-            <string extracomment="Tooltip text for Options window setting that sets the size of the database cache. Explains the corresponding effects of increasing/decreasing this value.">Maximum database cache size. A larger cache can contribute to faster sync, after which the benefit is less pronounced for most use cases. Lowering the cache size will reduce memory usage. Unused mempool memory is shared for this cache.</string>
+            <string extracomment="Tooltip text for Options window setting that sets the size of the database cache. Explains the corresponding effects of increasing/decreasing this value.">Maximum database cache size. Make sure you have enough RAM. A larger cache can contribute to faster sync, after which the benefit is less pronounced for most use cases. Lowering the cache size will reduce memory usage. Unused mempool memory is shared for this cache.</string>
            </property>
            <property name="text">
             <string>Size of &amp;database cache</string>

src/qt/optionsdialog.cpp

@@ -95,8 +95,7 @@ OptionsDialog::OptionsDialog(QWidget* parent, bool enableWallet)
     ui->verticalLayout->setStretchFactor(ui->tabWidget, 1);
 
     /* Main elements init */
-    ui->databaseCache->setMinimum(nMinDbCache);
-    ui->databaseCache->setMaximum(nMaxDbCache);
+    ui->databaseCache->setRange(nMinDbCache, std::numeric_limits<int>::max());
     ui->threadsScriptVerif->setMinimum(-GetNumCores());
     ui->threadsScriptVerif->setMaximum(MAX_SCRIPTCHECK_THREADS);
     ui->pruneWarning->setVisible(false);

src/txdb.h

@@ -25,8 +25,6 @@ class uint256;
 static const int64_t nDefaultDbCache = 450;
 //! -dbbatchsize default (bytes)
 static const int64_t nDefaultDbBatchSize = 16 << 20;
-//! max. -dbcache (MiB)
-static const int64_t nMaxDbCache = sizeof(void*) > 4 ? 16384 : 1024;
 //! min. -dbcache (MiB)
 static const int64_t nMinDbCache = 4;
 //! Max memory allocated to block tree DB specific cache, if no -txindex (MiB)