I'm using Spring Boot with Mongo 3.4 (in cluster with MongoS) The mongo client options configuration has the option cursorFinalizerEnabled.
According to documentation, this flag allows to:
Mongo Template closes the cursors. Making this true, spawns a thread on every new MongoClient.
Attempts to clean up DBCursors that are not closed.
MongoClientOptions options = MongoClientOptions.builder()
.cursorFinalizerEnabled(false)
.build();
What is the best practice? true or false? performance effect?
The default value of cursorFinalizerEnabled is true (see MongoClientOptions). So, your MongoClient will spawn this thread (and apply this behaviour) unless you choose not to.
This feature provides a safety net for client code which is (or might be) casual about handling cursors. So, depending on how you treat your cursors it might be useful or it might be a no-op.
The standard advice is: if your client code ensures that the close method of DBCursor is always invoked then you can set this to false. Otherwise, just accept the default.
As for the performance implications; it's hard to measure that. If your client code does not leave any open, unused cursors then it's a no-op but if your client code does leave open, unused cursors then this flag will help to reduce the impact on shared resources. Spawning a single thread to run this harvester seems like a low cost so if you are at all unsure about how your client code handles cursors then it's worth enabling it.
And, of course, as with all performance questions; the most reliable way of detemining the performance effect (if any) is to test with and without this flag and then compare :)