feat(rocksdb): Select the option of Direct-IO in Rocksdb (#450)

src/server/pegasus_server_impl.cpp

@@ -93,6 +93,28 @@ pegasus_server_impl::pegasus_server_impl(dsn::replication::replica *r)
     _db_opts.pegasus_data = true;
 
     // read rocksdb::Options configurations
+
+    _db_opts.use_direct_reads = dsn_config_get_value_bool(
+        "pegasus.server", "rocksdb_use_direct_reads", false, "rocksdb options.use_direct_reads");
+
+    _db_opts.use_direct_io_for_flush_and_compaction =
+        dsn_config_get_value_bool("pegasus.server",
+                                  "rocksdb_use_direct_io_for_flush_and_compaction",
+                                  false,
+                                  "rocksdb options.use_direct_io_for_flush_and_compaction");
+
+    _db_opts.compaction_readahead_size =
+        dsn_config_get_value_uint64("pegasus.server",
+                                    "rocksdb_compaction_readahead_size",
+                                    2 * 1024 * 1024,
+                                    "rocksdb options.compaction_readahead_size");
+
+    _db_opts.writable_file_max_buffer_size =
+        dsn_config_get_value_uint64("pegasus.server",
+                                    "rocksdb_writable_file_max_buffer_size",
+                                    1024 * 1024,
+                                    "rocksdb options.writable_file_max_buffer_size");
+
     _db_opts.write_buffer_size =
         (size_t)dsn_config_get_value_uint64("pegasus.server",
                                             "rocksdb_write_buffer_size",