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look transformation tune

原创 Linux操作系统 作者:ashleywzl 时间:2011-07-14 20:42:30 0 删除 编辑

Persistent cache. If you want to save and reuse the cache files, you can configure the transformation to use a persistent cache. Use this feature when you know the lookup table does not change between session runs. Using a persistent cache can improve performance because the Integration Service builds the memory cache from the cache files instead of from the database.

 

Overriding the ORDER BY Statement
By default, the Integration Service generates an ORDER BY statement for a cached lookup. The ORDER BY statement contains all lookup ports. To increase performance, you can suppress the default ORDER BY statement and enter an override ORDER BY with fewer columns.

The Integration Service always generates an ORDER BY statement, even if you enter one in the override. Place two dashes `--' after the ORDER BY override to suppress the generated ORDER BY statement.

eg--SELECT ITEMS_DIM.ITEM_NAME, ITEMS_DIM.PRICE, ITEMS_DIM.ITEM_ID FROM  ITEMS_DIM ORDER BY ITEMS_DIM.ITEM_ID, ITEMS_DIM.PRICE --

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