mongodb read write locks I'm currently investigating the possibility of using mongodb. This would contain the a collection of 100million+ documents. I need a process that will be constantly running deleting documents older than some expiry data. I will have new documents constantly going into this. I will also have big updates occuring that may need to update X million document to change the expiry date because a tenant has changed their retention policy. At the same time a front end will be reading this data to show a report which can be filtered.

Reading the mongodb documentation it looks like when I do a write I'll be locking out the reads until the writes have completed. Is there a better way to prevent the expiry of old documents and updating of expiry dates blocking the front ended display this data in a report?
I need a process that will be constantly running deleting documents
  older than some expiry data.


This you can do it by creating a Time to live(TTL) on the expiration date. TTL indexes are special single-field indexes that MongoDB can use to automatically remove documents from a collection after a certain amount of time or at a specific clock time. 


  Reading the MongoDB documentation it looks like when I do a write I'll
  be locking out the reads until the writes have completed.


MongoDB wired tiger storage engine gives document level locking. So, in this case, only the documents that are being updated/inserted will be locked. Other documents are available to read.