database - Download one thing at time or the entire db? -

database - Download one thing at time or the entire db? -

i developing sort of question-answers illustration app in javascript, transformed in smartphone app. questions , reply on db.

my question one: improve everytime want question on screen app makes ajax connection server , retrieve finish question-answer json object... or retrieve questions , answers first time , move logic within client?..

i'd know if there guidelines follow or rules create decisions on..

i.b.

if know client need info should provide in 1 go. exception rule if info big , exhaust resource network, cpu or memory if taken @ once. in case little chunks appropriate.

database performance