create index with PARALLEL option 原理

最新推荐文章于 2025-05-22 14:14:57 发布

clwwf2015

最新推荐文章于 2025-05-22 14:14:57 发布

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本文介绍了一种通过并行处理来创建索引的方法。该方法首先对表进行随机采样，找到可以将索引等分为指定并行度数量的键值。接着一组查询进程扫描表，提取键值和行ID对，并将这些对发送到另一组进程。第二组进程对键值进行排序并按常规方式构建索引。最后，各部分索引由并行协调器连接形成最终的完整索引。

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CREATE INDEX indx_name ON schema.table_name(column_name) PARALLEL n;

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The table is randomly sampled and a set of index keys is found that equally divides the index into the same number of pieces as the specified degree of parallelism. A first set of query processes scans the table ,extracts key,row ID pairs,and sends each pair to a process in a second set of query processes based on key.Each process in the second set sorts the keys and builds an index in the usual fashion.After all index pieces are built,the parallel coordinator concatenates the pieces (whice are ordered) to form. the final index.

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转载于:http://blog.itpub.net/10714335/viewspace-374918/