Are indexes good or bad for a large database?

Posted by gmemon on Stack Overflow See other posts from Stack Overflow or by gmemon
Published on 2010-04-26T07:45:45Z Indexed on 2010/04/26 7:53 UTC
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mysql

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indexes

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Performance

Hello All,

I read on MySQL Performance Blog that when tables are large, it is better to scan full tables, instead of using indexes.

I have a table with tens of millions of rows. When conducting queries, if I use no indexes, then queries are 24 times slower than with indexes. I know lot of things may cause this (e.g., are rows stored sequentially), but can you please give me some hints what might be happening? Or how I should start examining this issue? I want to understand when use of indexes is preferred and when it's not

Thanks

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