coins: derive batch_write_bytes from -dbcache when unspecified

Extend `ReadCoinsViewArgs` to dynamically set `batch_write_bytes` using `GetDbBatchSize()` when `-dbbatchsize` is not explicitly provided.

This enables larger LevelDB batches on systems with high `-dbcache` values, which reduces the number of write operations during UTXO flushes and improves I/O efficiency, particularly during AssumeUTXO loads and IBD.

src/init.cpp

@@ -48,6 +48,7 @@
 #include <node/caches.h>
 #include <node/chainstate.h>
 #include <node/chainstatemanager_args.h>
+#include <node/coins_view_args.h>
 #include <node/context.h>
 #include <node/interface_ui.h>
 #include <node/kernel_notifications.h>
@@ -487,7 +488,7 @@ void SetupServerArgs(ArgsManager& argsman, bool can_listen_ipc)
     argsman.AddArg("-coinstatsindex", strprintf("Maintain coinstats index used by the gettxoutsetinfo RPC (default: %u)", DEFAULT_COINSTATSINDEX), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     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 | 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("-dbbatchsize", strprintf("Maximum database write batch size in bytes (default: calculated from the `-dbcache` value or %u if not set)", node::GetDbBatchSize(DEFAULT_DB_CACHE)), 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("-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);

src/node/coins_view_args.cpp

@@ -2,6 +2,8 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <kernel/caches.h>
+
 #include <node/coins_view_args.h>
 
 #include <common/args.h>
@@ -10,7 +12,9 @@
 namespace node {
 void ReadCoinsViewArgs(const ArgsManager& args, CoinsViewOptions& options)
 {
-    if (auto value = args.GetIntArg("-dbbatchsize")) options.batch_write_bytes = *value;
+    if (const auto value = args.GetIntArg("-dbbatchsize")) options.batch_write_bytes = *value;
-    if (auto value = args.GetIntArg("-dbcrashratio")) options.simulate_crash_ratio = *value;
+    else options.batch_write_bytes = GetDbBatchSize(args.GetIntArg("-dbcache", DEFAULT_KERNEL_CACHE));
+
+    if (const auto value = args.GetIntArg("-dbcrashratio")) options.simulate_crash_ratio = *value;
 }
 } // namespace node

src/txdb.h

@@ -8,6 +8,7 @@
 
 #include <coins.h>
 #include <dbwrapper.h>
+#include <kernel/caches.h>
 #include <kernel/cs_main.h>
 #include <sync.h>
 #include <util/fs.h>
@@ -21,16 +22,13 @@
 class COutPoint;
 class uint256;
 
-//! -dbbatchsize default (bytes)
-static const int64_t nDefaultDbBatchSize = 16 << 20;
-
 //! User-controlled performance and debug options.
 struct CoinsViewOptions {
     //! Maximum database write batch size in bytes.
-    size_t batch_write_bytes = nDefaultDbBatchSize;
+    size_t batch_write_bytes{DEFAULT_DB_CACHE_BATCH};
     //! If non-zero, randomly exit when the database is flushed with (1/ratio)
     //! probability.
-    int simulate_crash_ratio = 0;
+    int simulate_crash_ratio{0};
 };
 
 /** CCoinsView backed by the coin database (chainstate/) */