Is incrementing a field in MySQL atomic?

Question

I\'m making a web site where I would like to increment a counter in a standard MyISAM table.

Simplified example:

UPDATE votes SET num = num + 1;
         


        

Answer 1

Another approach when using InnoDB is using unique index on multiple column as follow:

Table 'Sessions' { unique_key(browser_session_id,profile_id) // ensures that inserting 1 entry per session will occur once }

select count(browser_session_id) from Sessions

Will guarantee result of unique sessions, as multiple sessions per user is not allowed.

Conclusions

• Advantage

  Each insert does require a pre-select.

• Disadvantage

  It is not suitable for all cases.

  May slow down write performance, and requires extra management