Hi all! I apologize in advance for the vague question, but I'm facing a weird behaviour in my application. I'm saving a fair amount (about 100k) of documents through mongoose by using the normal save method (I need the middleware functions). Every save is preceded by a find to verify if a document already existed and is being updated or if it is a new insertion. Also documents are saved in parallel through async.map. It happens that after a about 50k documents saved, mongoose seems to freeze intermittently and saves begin to be issued very slowly (I get delays up to 3 seconds between them, when normally they don't take more than 10ms). It doesn't appear to be Mongo's fault by looking at the info provided by mongostat. I also have more than 3GB of free memory on the machine so that shouldn't be a problem as well. Could it be something related to how Mongoose works? Maybe something related to Promises? How could I debug the problem? Thanks and sorry for the wall of text.