1. Samsung index concept

Samsung index The concept of is more tongue twister , I understood it myself and sorted it out ：

1. B+ Try to put the adjacent records on the tree together

2. The order of data in the index is consistent with that in the search , That is to say order by and group by Try to keep the fields in the same order as the index .

3. Try to overwrite the index , Avoid returning to your watch .

2.  Several optimization suggestions for index  

1. Search only ,order by,group by Create index for query column ;

2. Try to use Samsung index ;

3. The primary key column should not update, Best use insert;

4. Do not create indexes on redundant and duplicate columns . The calculation formula refers to the previous blog .

5. Unused index delete

3. mysql-cost Value costing

Calculation cost Let's say before it's worth it I/0 Time and CPU Time

I/0 Time = Seek time + Rotation time + Transmission time ( once I/0 It's about time 9-10ms about ), Among them, the seek time is the longest , Because he is a mechanical movement , The rotation time is very fast , Usually, the number of revolutions of our computer is usually thousands or 1 More than ten thousand , The transmission time is ns level , negligible . The biggest waste of time is when searching for a way