DbConnectionOptions.ParseInternal(Dictionary`2 parsetable, String connectionString, Boolean buildChain, Dictionary`2 synonyms, Boolean firstKey)
DbConnectionOptions.ctor(String connectionString, Dictionary`2 synonyms)
SqlConnectionString.ctor(String connectionString)
SqlConnectionFactory.CreateConnectionOptions(String connectionString, DbConnectionOptions previous)
DbConnectionFactory.GetConnectionPoolGroup(DbConnectionPoolKey key, DbConnectionPoolGroupOptions poolOptions, DbConnectionOptions& userConnectionOptions)
SqlConnection.ConnectionString_Set(DbConnectionPoolKey key)
SqlConnection.set_ConnectionString(String value)
SqlConnection.ctor(String connectionString)
Checkpoint.Reset(String nameOrConnectionString)
          
I found I forget use NpgsqlConnection like
using (var conn = new NpgsqlConnection("ConnectionString"))
    await conn.OpenAsync();
    await checkpoint.Reset(conn);