fix(NODE-4845): allocate sessions lazily in cursors #4575
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Description
What is changing?
When no explicit session is provided to a cursor, we now instantiate an implicit session when initializing the cursor, instead of in the cursor's constructor.
Release Highlight
Cursors lazily instantiate sessions
In previous versions, sessions were eagerly allocated whenever a cursor was created, regardless of whether or not a cursor was actually iterated (and the session was actually needed). Some driver APIs (
FindCursor.count(),AggregationCursor.explain()andFindCursor.explain()) don't actually iterate the cursor they are executed on. This can lead to client sessions being created and never being cleaned up.With this update, sessions are not allocated until the cursor is iterated.
Double check the following
npm run check:lintscripttype(NODE-xxxx)[!]: descriptionfeat(NODE-1234)!: rewriting everything in coffeescript