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Re: Questions about performance for huge table (100M+ rows)
Posted by: Rick James
Date: January 05, 2009 06:49PM

The EXPLAIN will probably show that "SELECT ... ORDER BY un-indexed-column LIMIT..." is doing a "table scan" and "filesort".

The 5% improvement was either coincidence or caching -- probably it was not any real improvement.

Depending on how serious you are about these queries, we can talk about adding indexes (and the drawbacks for huge tables), summary tables (and the hassle of maintaining them), etc.

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