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    <p>A common misconception for database users is that high CPU use is bad.</p> <p>It isn't.</p> <p>A database has exactly one speed: as fast as possible. It will always use up every resource it can, within administrator set limits, to execute your queries quickly.</p> <p>Most queries require lots more of one particular resource than others. For most queries on bigger databases that resource is disk I/O, so the database will be thrashing your storage as fast as it can. While it is waiting for the hard drive it usually can't do any other work, so that thread/process will go to sleep and stop using the CPU.</p> <p>Smaller databases, or queries on small datasets within big databases, often fit entirely in RAM. The operating system will cache the data from disk and have it sitting in RAM and ready to return when the database asks for it. This means the database isn't waiting for the disk and being forced to sleep, so it goes all-out processing the data with the CPU to get you your answers quickly.</p> <p>There are two reasons you might care about CPU use:</p> <ul> <li>You have something else running on that machine that isn't getting enough CPU time; or</li> <li>You think that given the 100% cpu use you aren't getting enough performance from your database</li> </ul> <p>For the first point, don't blame the database. It's an admin issue. Set operating system scheduler controls like nice levels to re-prioritize the workload - or get a bigger server that can do all the work you require of it without falling behind.</p> <p>For the second point you need to look at your database tuning, at your queries, etc. It's not a "database uses 100% cpu" problem, it's a "I'm not getting enough throughput and seem to be CPU-bound" problem. Database and query tuning is a big topic and not one I'll get into here, especially since I don't generally use MySQL.</p>
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    1. USCraig Ringer
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    1. COhi craig, thanks for the reply. No other app running more than 1% of the CPU. Yes , i follow standard MySQL tuning, doing the cache query and other things. The answer to a bigger server is a YES, but that will not be in 3 months time. I just want to know whether i can utilize current resource to its limit with other RDBMS or do some code tuning.
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    2. COOK, so your problem isn't high CPU usage. It's that you want more throughput than you are getting, and you are currently bottlenecked on CPU. @pakcikkantin
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    3. CO@pakcikkantin I can't really help you with the tuning part; I focus almost entirely on PostgreSQL. If it's anything like PostgreSQL then adding a connection pool to limit the number of concurrent connections fighting for resources should make things go quite a lot faster if you have lots of concurrent queries. Beyond that, I suggest posting a better question with details on your workload, your queries, EXPLAIN output, your RAM and database sizes, etc; all the things someone will need to know to actually help you tune. Try the MySQL forums; probably better than here for tuning.
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