Does RocksDB collapse merge arguments during reads if PartialMerge is specified

Question

Both RocksDB dev group and FB page seems unresponsive so I'm asking the question here.

I'm wondering if RocksDB collapses merge arguments on every read of PartialMerge operator is specified? Particularly the use case looks like this:

1. There is a single column db which stores a number
2. Both FullMerge/PartialMerge operators are specified and simply computing the sum of values.
3. We write a key/value pairs: ("some_key", 1), ("some_key", 1), ("some_key", 1). 3') No compaction happened here
4. We read the value for key "some_key": I expected 3 reads to occur returning the value 3.
5. We read again the value for key "some_key": here is the question if rocksdb will perform 1 or 3 reads?

Answer 1

Afaik, rocksdb merges the value on the read path - so the second read would only be 1 read - since the value has already been merged/collapsed