performance - MySQL query speed or rows read -


sorry lots of useless text. important stuff told on last 3 paragraphs :d

recently had mysql problem in 1 of client servers. out of blue starts sky-rocking cpu of mysql process. problem lead finding , optimizing bad queries , here problem.

i thinking optimization speeding queries (total time needed query execute). after optimizing several queries towards colleague starting colleague started complaining queries read many rows, rows table (as shown explain).

after rewriting query noticed that, if want query read less rows - query speed suffers, if query made speed - more rows read.

and didn't make me sense: less rows read, execution time longer

and made me wonder should done. of course perfect have fast query reads least rows. since doesn't seem possible me, i'm searching answers. approach should take - speed or less rows read? pros&cons when query fast more rows read , when less rows read speed suffer? happens server @ different cases?

after googling find articles , discussions how improve speed, neither covered different cases mentioned before.

i'm looking forward seeing personal choices of course reasoning. links direct me right way welcome too.

i think problem depends on how limiting amount of rows read. if read less rows implementing more clauses mysql needs run against, yes, performance take hit.

i @ perhaps indexing of columns make search more complex. simple data types faster lookup complex ones. see if searching toward indexed columns.


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