在執行查詢時，Mysql預設把結果全部load到記憶體後再返回（這種模式可理解為Oracle的ALL_ROWS最佳化模式），如果表資料量太大的話，會導致記憶體溢位。
1.在mysql console連線資料庫時：
加入-q選項，mysql -h hostname -u root -p -q

2.在jdbc連線資料庫時：
在連線串中加入useCursorFetch=true

在建立的語句中，加入setFetchSize，如
stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,java.sql.ResultSet.CONCUR_READ_ONLY);
stmt.setFetchSize(Integer.MIN_VALUE);

注意：The Integer.MIN_VALUE is used by the MySQL driver as a signal to switch to streaming result set mode. It is not used as a value.
See the documentation, under "Resultset". In summary:
By default, ResultSets are completely retrieved and stored in memory. You can tell the driver to stream the results back one row at a time by setting stmt.setFetchSize(Integer.MIN_VALUE); (in combination with a forward-only, read-only result set).

Mysql大表查詢注意事項

相關文章