Manual:$wgHitcounterUpdateFreq

Details
Sets how often page counters should be updated, higher values are easier on the database. A value of 1 causes the counters to be updated on every hit, any higher value n cause them to update on average every n hits. Should be set to either 1 or something largish, e.g. 1000, for maximum efficiency.

To disable the page counters entirely, set $wgDisableCounters to true.