code: @Override
      public void destroy() {
          if (!isClosed) {
              isClosed = true;
  
              cachedStatementPool.close();
  
              try {
                  internalConn.close();
              } catch (SQLException e) {
                  // ignore;
  
                  if (logger.isWarnEnabled()) {
                      logger.warn(AbacusException.getErrorMsg(e));
                  }
              } finally {
                  if (connManager != null) {
                      connManager.detroyConnection(this);
                  }
              }
          }
      }
docs: To release resourse of the <tt>AbstractPoolable</tt>.
  
  @see com.landawn.abacus.pool.Poolable#destroy()