arekdygas commented on issue #1152: Inconsistent sum and sumsqr aggregates of 
floating point numbers
URL: https://github.com/apache/couchdb/issues/1152#issuecomment-364258099
 
 
   Integers work ok in CouchDB 2.1.1 (single node with 8 shards).
   
   Out of curiosity I did some tests in JS engine used by Chrome:
   -0.1-0.2+0.1+0.2 = -2.7755575615628914e-17
   0.1+0.2-0.1-0.2 = 2.7755575615628914e-17
   other combinations = 0
   
   which are exact results from my test case.
   
   I don't really know how CouchDB internally works, but I think it reads 
aggregates from shards and then calculates final aggregate. That would explain 
this issue, if shards results are returned in random order. But it looks that 
in Cloudant they are always returned in the same order, making the result the 
same across multiple requests.

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