网站 › 『 Sybase Other 』 › [求助]sybase执行计划索引问题求助。

randy546 发表于 2007-10-29 09:42:45

[求助]sybase执行计划索引问题求助。

<p>使用执行计划查看的时候其中2张表的使用情况如下：</p><p>其中一张表的索引使用情况是：&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </p><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Positioning at index start. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Index contains all needed columns. Base table will not be read. </p><p>而另一张表的使用情况是：</p><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Positioning by key. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Keys are: <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; custid&nbsp; ASC </p><p>请问下是不是上面的Positioning at index start.是没有用到索引的？还是什么情况啊？执行的时候效率很低！</p><p></p><p>谢谢了！</p><p></p><p>FROM TABLE <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tc_servbaseinfo <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; b <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Nested iteration. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Index : XIE7tc_servbaseinfo <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Forward scan. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Positioning at index start. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Index contains all needed columns. Base table will not be read. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Using I/O Size 16 Kbytes for index leaf pages. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; With LRU Buffer Replacement Strategy for index leaf pages. </p><p><br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; FROM TABLE <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tc_custbaseinfo <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; c <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Nested iteration. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Using Clustered Index. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Index : tc_custbas_17405822582 <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Forward scan. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Positioning by key. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Keys are: <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; custid&nbsp; ASC <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Executed in parallel with a 4-way hash scan. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Using I/O Size 2 Kbytes for index leaf pages. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; With LRU Buffer Replacement Strategy for index leaf pages. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Using I/O Size 2 Kbytes for data pages. <br/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; With LRU Buffer Replacement Strategy for data pages. <br/></p>

randy546 发表于 2007-10-29 09:56:51

没人知道指点下买？？

songsh 发表于 2007-11-4 17:21:52

<p>不是没用到索引， 而是上面的用的索引不合理 所以才效率低</p>

lovelyni 发表于 2007-12-19 22:06:42

来顶一下

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