If one wants to count the number of documents in an index (of Elasticsearch) then there are (at least?) two possibilities:
Direct count
POST my_index/_count
should return the number of documents in my_index.
Using search
Here one can use the count as the search_type or some other type. In either of the cases the total count can be extracted from the field ['hits']['total']
My questions are:
what is the difference between the different approaches? Which one should I prefer?
I raise this question because I'm experiencing different results depending on the chosen method. I'm now in the process of debugging the issue, and this question popped up.
Probably _count is a bit faster since it doesn't have to execute a full query with ranking and result fetching and can simply return the size.
It would be interesting to know a bit more about how you manage to get different results though. For that I need more information like what exact queries you are sending and if any indexing is going on on the index.
But suppose that you do the following
_search and _count (with a match all query) should return the same total. If not, that'd be very weird.