Graph:
A -- B
Solution with seed 0:
INDEXED_NESTED_LOOP_JOIN
---leftEmbeddingField: (none)
---rightEmbeddingField: b
---joinPredicates:
------a = b
---Outer:
------COLLSCAN
---------ns = test.a
---------filter = $and
---------nodeId = 1
---------fetched = 1
---------sortedByDiskLoc = 0
---------providedSorts = {baseSortPattern: {}, ignoredFields: []}
---Inner:
------FETCH
---------ns = test.b
---------nodeId = 3
---------fetched = 1
---------sortedByDiskLoc = 0
---------providedSorts = {baseSortPattern: {}, ignoredFields: []}
---------Child:
------------INDEX_PROBE
---------------Namespace: test.b Index: { b: 1 }

Solution with seed 1:
INDEXED_NESTED_LOOP_JOIN
---leftEmbeddingField: b
---rightEmbeddingField: (none)
---joinPredicates:
------b = a
---Outer:
------COLLSCAN
---------ns = test.b
---------filter = $and
---------nodeId = 1
---------fetched = 1
---------sortedByDiskLoc = 0
---------providedSorts = {baseSortPattern: {}, ignoredFields: []}
---Inner:
------FETCH
---------ns = test.a
---------nodeId = 3
---------fetched = 1
---------sortedByDiskLoc = 0
---------providedSorts = {baseSortPattern: {}, ignoredFields: []}
---------Child:
------------INDEX_PROBE
---------------Namespace: test.a Index: { a: 1 }

