Add DynamicMemoryUsage() to LevelDB

This adds a DynamicMemoryUsage() method similar to the existing methods
of the same name, and adds logging of memory usage to
CDBWrapper::WriteBatch.

src/dbwrapper.cpp

@@ -89,6 +89,7 @@ static leveldb::Options GetOptions(size_t nCacheSize)
 }
 
 CDBWrapper::CDBWrapper(const fs::path& path, size_t nCacheSize, bool fMemory, bool fWipe, bool obfuscate)
+    : m_name(fs::basename(path))
 {
     penv = nullptr;
     readoptions.verify_checksums = true;
@@ -155,11 +156,30 @@ CDBWrapper::~CDBWrapper()
 
 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;
+    }
     leveldb::Status status = pdb->Write(fSync ? syncoptions : writeoptions, &batch.batch);
     dbwrapper_private::HandleError(status);
+    if (log_memory) {
+        double mem_after = DynamicMemoryUsage() / 1024 / 1024;
+        LogPrint(BCLog::LEVELDB, "WriteBatch memory usage: db=%s, before=%.1fMiB, after=%.1fMiB\n",
+                 m_name, mem_before, mem_after);
+    }
     return true;
 }
 
+size_t CDBWrapper::DynamicMemoryUsage() const {
+    std::string memory;
+    if (!pdb->GetProperty("leveldb.approximate-memory-usage", &memory)) {
+        LogPrint(BCLog::LEVELDB, "Failed to get approximate-memory-usage property\n");
+        return 0;
+    }
+    return stoul(memory);
+}
+
 // Prefixed with null character to avoid collisions with other keys
 //
 // We must use a string constructor which specifies length so that we copy

src/dbwrapper.h

@@ -198,6 +198,9 @@ private:
     //! the database itself
     leveldb::DB* pdb;
 
+    //! the name of this database
+    std::string m_name;
+
     //! a key used for optional XOR-obfuscation of the database
     std::vector<unsigned char> obfuscate_key;
 
@@ -284,6 +287,9 @@ public:
 
     bool WriteBatch(CDBBatch& batch, bool fSync = false);
 
+    // Get an estimate of LevelDB memory usage (in bytes).
+    size_t DynamicMemoryUsage() const;
+
     // not available for LevelDB; provide for compatibility with BDB
     bool Flush()
     {