How long does it cost to get the database back? How long does it cost to write a disk?

How long does it cost to determine the database return? How long does it cost to write a disk?
To write data to a file after the database has been queried, but the wait time is too slow to find out where it takes longer, about 800,000 of the data, what methods can be traced to query time consuming and write disk Time
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Step time time should be OK, can use microtime precision to subtle
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These data, the general database will have internal variables, not the front-end PHP is concerned about, and generally not by the front-end to calculate.

such as MySQL with show global status; Can get a lot of internal information, including memory, disk usage and so on.

Specifically, you can use the database for Google to look under the

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