Querying MongoDB with a regular expression exceeding 32764 characters in length silently fails without returning any results or raising any errors.

An example of this behaviour is as follows.

Create a document in the mongo shell:

  > String.prototype.repeat = function(n) { return new Array(n + 1).join(this) }
  function (n) {
      return (new Array(n + 1)).join(this);
  }
  > db.example.insert({ field : "x".repeat(50000) })

Querying for the document with a 32764 character regular expression will return a result as expected:

  > db.example.find({ field : { $regex : "x".repeat(32764) }})
  > { "_id" : ObjectId("4f9e1678d3eff3503675d2be"), "field" : "..." }

Querying for a document with a 32765 character regular expression fails with no errors nor results:

  > db.example.find({ field : { $regex : "x".repeat(32765) }})
  >

As per Eliot on the mongodb-user list:

"That looks like the default pcre max size.
Can you open a ticket @ jira.mongodb.org to see if its possible to
increase the size?"