Add $min/max update modifiers which leave/replace the existing field based on the comparison of a provided value.

Note: if the field is missing then the value supplied will replace it like it was specified via a $set.

Examples:

> db.v.find()
{_id:1, v:1}
{_id:2, v:2}
{_id:3}
{_id:4}
> db.v.update({_id:1}, {$min: {v: 2}} // do not change the doc, existing value is smaller
> db.v.update({_id:1}, {$min: {v: 0}} // set v to 0
> db.v.findOne({_id:1})
{_id:1, v:0}

> db.v.update({_id:2}, {$max: {v: 1}} // do not change the doc, existing value is larger
> db.v.update({_id:2}, {$max: {v: 2}} // do not change the doc, existing value is the same
> db.v.update({_id:2}, {$max: {v: 200}} // set v to 200
> db.v.findOne({_id:2})
{_id:2, v:200}

> db.v.update({_id:3}, {$min: {v: 2}} // set v to 2
{_id:3, v:2}
> db.v.update({_id:4}, {$max: {v: 2}} // set v to 2
{_id:4, v:2}

old description
I'm working on a realtime website performance analysis tool, were a number of parallel processes import data into a mongodb instance.

In this context, it would be extremely helpful to have $max and $min update operators which would work similar to $inc.

{ $min :

}

sets field to new value if field does not exist or value is smaller than current field value.

{ $max :

}

sets field to new value if field does not exist or value is larger than current field value.