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   to true.

Technical details
When this setting is set to a number bigger than 1, the page id of any page viewed is stored in the   table. About 1 in every ( )*0.25 hits, the number of entries in the hit counter table is checked. If there is more than   entries in the   table, then those pageviews are transfered in batch to the   field (and the   table is emptied).