1 files changed, 29 insertions, 3 deletions

diff --git a/src/dbwrapper.cpp b/src/dbwrapper.cpp
index fb0d4215a2..ca446c92fe 100644
--- a/src/dbwrapper.cpp
+++ b/src/dbwrapper.cpp
@@ -4,6 +4,7 @@
 
 #include <dbwrapper.h>
 
+#include <memory>
 #include <random.h>
 
 #include <leveldb/cache.h>
@@ -71,6 +72,31 @@ public:
     }
 };
 
+static void SetMaxOpenFiles(leveldb::Options *options) {
+    // On most platforms the default setting of max_open_files (which is 1000)
+    // is optimal. On Windows using a large file count is OK because the handles
+    // do not interfere with select() loops. On 64-bit Unix hosts this value is
+    // also OK, because up to that amount LevelDB will use an mmap
+    // implementation that does not use extra file descriptors (the fds are
+    // closed after being mmaped).
+    //
+    // Increasing the value beyond the default is dangerous because LevelDB will
+    // fall back to a non-mmap implementation when the file count is too large.
+    // On 32-bit Unix host we should decrease the value because the handles use
+    // up real fds, and we want to avoid fd exhaustion issues.
+    //
+    // See PR #12495 for further discussion.
+
+    int default_open_files = options->max_open_files;
+#ifndef WIN32
+    if (sizeof(void*) < 8) {
+        options->max_open_files = 64;
+    }
+#endif
+    LogPrint(BCLog::LEVELDB, "LevelDB using max_open_files=%d (default=%d)\n",
+             options->max_open_files, default_open_files);
+}
+
 static leveldb::Options GetOptions(size_t nCacheSize)
 {
     leveldb::Options options;
@@ -78,13 +104,13 @@ static leveldb::Options GetOptions(size_t nCacheSize)
     options.write_buffer_size = nCacheSize / 4; // up to two write buffers may be held in memory simultaneously
     options.filter_policy = leveldb::NewBloomFilterPolicy(10);
     options.compression = leveldb::kNoCompression;
-    options.max_open_files = 64;
     options.info_log = new CBitcoinLevelDBLogger();
     if (leveldb::kMajorVersion > 1 || (leveldb::kMajorVersion == 1 && leveldb::kMinorVersion >= 16)) {
         // LevelDB versions before 1.16 consider short writes to be corruption. Only trigger error
         // on corruption in later versions.
         options.paranoid_checks = true;
     }
+    SetMaxOpenFiles(&options);
     return options;
 }
 
@@ -159,12 +185,12 @@ bool CDBWrapper::WriteBatch(CDBBatch& batch, bool fSync)
     const bool log_memory = LogAcceptCategory(BCLog::LEVELDB);
     double mem_before = 0;
     if (log_memory) {
-        mem_before = DynamicMemoryUsage() / 1024 / 1024;
+        mem_before = DynamicMemoryUsage() / 1024.0 / 1024;
     }
     leveldb::Status status = pdb->Write(fSync ? syncoptions : writeoptions, &batch.batch);
     dbwrapper_private::HandleError(status);
     if (log_memory) {
-        double mem_after = DynamicMemoryUsage() / 1024 / 1024;
+        double mem_after = DynamicMemoryUsage() / 1024.0 / 1024;
         LogPrint(BCLog::LEVELDB, "WriteBatch memory usage: db=%s, before=%.1fMiB, after=%.1fMiB\n",
                  m_name, mem_before, mem_after);
     }