Question

我有一个包含大约7M行的表和一个SSIS包，它使用如下语句更新该表中的5.6M行。

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然后我启动几个大型select语句，它们对MERGE INTO Target t USING ( select ID, Type from SomeTable ) s ON (t.ID = s.ID) WHEN MATCHED THEN UPDATE SET t.Type = s.Type进行内连接。我从那些select语句中得到了ORA-01555（快照太旧：回滚段号字符串，名称“字符串”太小）。这看起来像MERGE语句在提交完成之前返回。我最初的想法是增加回滚段的大小（这无疑会引入完整性问题），但我们的DBA并不热衷于这个想法。他们建议我在开始选择语句之前等待1分钟。（对我来说，与人工等待同步是一个危险信号。）

我的问题是，有没有办法确保在MERGE语句返回之前MERGE提交已经完成？对我来说，这将解决问题。

Answer 1

我会避免合并整个表格（如果可能的话）：

MERGE INTO Target t
USING( select ID, Type
      from SomeTable
      where some_kind_of_timestamp_column > date_of_last_incremental_load
) s
ON (t.ID = s.ID)
WHEN MATCHED THEN UPDATE SET t.Type = s.Type
                  WHERE (t.Type != s.Type)
                    OR (t.Type IS NULL AND s.TYPE IS NOT NULL)
                    OR (t.Type IS NOT NULL AND s.TYPE IS NULL)
                  -- there is no need for updating A -> A

COMMIT;

-- some select

Oracle MERGE语句在提交完成之前是否返回

1 个答案: