On 05/07/2014 06:27 PM, Tom Lane wrote:
I think you're just proving the point that this code is woefully
underdocumented.  If there were, somewhere, some comment explaining
what the heck JB_ROOT_COUNT actually counts, maybe I wouldn't be asking
this question.  jsonb.h is certainly not divulging any such information.

After having reverse-engineered the convertJsonb code, I think I can explain what JB_ROOT_COUNT is.

If the root of the Jsonb datum is an array, it's the number of elements in that top-level array. If it's an object, it's the number of key/value pairs in that top-level object. Some of the elements of that array (or values of the object) can be arrays or objects themselves.

gin_extract_jsonb recursively extracts all the elements, keys and values of any sub-object too, but JB_ROOT_COUNT only counts the top-level elements.

(I hope this is made a bit more clear in the comments I added in the patch I posted this morning)

- Heikki

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