enhance default value in configuration

[HarrisChu]

should enhance default value in configuration, so user would change less items if using in production.

e.g.

--rocksdb_block_cache=4096
--rocksdb_db_options={"max_subcompactions":"4","max_background_jobs":"4"}

# storage
DEFINE_int32(reader_handlers, 32, "Total reader handlers");
DEFINE_int32(num_worker_threads, 32, "Number of workers");

# graph
DEFINE_int32(num_worker_threads, 0, "Number of threads to execute user queries");

  if (FLAGS_num_worker_threads == 0) {
    FLAGS_num_worker_threads = std::thread::hardware_concurrency();
  }

DEFINE_bool(enable_partitioned_index_filter, false, "True for partitioned index filters");

[dbacyj]

DEFINE_int32(meta_http_thread_num, 3, "Number of meta daemon's http thread");
DEFINE_uint64(raft_snapshot_timeout, 60 * 5, "Max seconds between two snapshot requests");
DEFINE_int32(snapshot_worker_threads, 4, "Threads number for snapshot");
DEFINE_int32(snapshot_io_threads, 4, "Threads number for snapshot");
DEFINE_uint32(snapshot_part_rate_limit, 1024 * 1024 * 10, "max bytes of pulling snapshot for each partition in one second");

[xiajingchun]

add 2 items to be considered:

• wal_ttl
• rocksdb block_size