`MongoObservationCommandListener` causes memory leak

[michaldo]

Spring data mongodb 4.5.4

I use https://docs.spring.io/spring-data/mongodb/reference/observability/observability.html and https://docs.spring.io/spring-data/mongodb/reference/mongodb/change-streams.html#change-streams-with-messagelistener

I have one change stream listener with one thread which runs continously

When I debug listener thread and method MongoObservationCommandListener#commandStarted, I see in first call parent observation is null

L117

Found the following observation passed from the mongo context [null]

And in L123 new observation is created, let name it O1

In next call, I see

Found the following observation passed from the mongo context: O1

(of cource it is no "O1" but long json describing O1)

And in L123 new observation O2 is created and in L128 O2.setParent(O1)

In next call, I see

Found the following observation passed from the mongo context: O2

And in L123 new observation O3 is created and in L128 O3.setParent(O2)

Over and over up to OOM

Additionally, when logs are enabled, the following contradictory sequence is printed

mongo-listener] [] [-] [ / ] o.s.d.m.o.MongoObservationCommandListener: Instrumenting the command started event
mongo-listener] [] [-] [ / ] o.s.d.m.o.MongoObservationCommandListener: No observation was found - will not create any child observations
mongo-listener] [] [-] [ / ] o.s.d.m.o.MongoObservationCommandListener: Found the following observation passed from the mongo context [null]
mongo-listener] [] [-] [ / ] o.s.d.m.o.MongoObservationCommandListener: Created a child observation [{name=spring.data.mongodb.command(null)...****

[mp911de]

The problem is that we're creating new observations and setting it as the current one resulting that all subsequent commands become children. This is wrong in the first place because nesting should only occur for truly nested commands and not unconditionally. This nesting leads to a massive allocation of Observations.