A.There is no major difference between them. $addToSet is a deprecated version of $push.

B.$addToSet adds the item to the field only if the new item is of the same datatype

C.$addToSet adds the item to the field only if it does not exist already; while $push pushes the item to the field irrespective of whether it was present or not

D.$addToSet needs the fields to be already present while $push will work even if the field is not present

A.db.posts.find( { post_timestamp: { $fieldtype: 10 } } )

B.db.posts.find( { post_timestamp: { $fieldtype: null } } )

C.db.posts.find( { post_timestamp : { $type; 10 > > )

D.db.posts.find( { post_timestamp: { $type: null } } )

A.hidden

B.arbiter

C.primary

D.secondary

A.customExecutionStats

B.executionStats

C.allPlansExecution

D.queryPlanner

A.There is no maximum size. It depends on the RAM.

B.16 MB

C.12 MB

D.2 MB