520lailai opened a new issue, #356:
URL: https://github.com/apache/datasketches-cpp/issues/356
I compared the datasketches-java and datasketches-cpp, found that the
different behavior of JAVA and C++.
refer to the code below:
datasketches::update_theta_sketch update_sketch1 =
datasketches::update_theta_sketch::builder().set_lg_k(14).build();
for(int i = 0; i < 16384; i++) update_sketch1.update(i);
datasketches::update_theta_sketch update_sketch2 =
datasketches::update_theta_sketch::builder().set_lg_k(14).build();
for(int i = 0; i < 26384; i++) update_sketch2.update(i);
datasketches::update_theta_sketch update_sketch3 =
datasketches::update_theta_sketch::builder().set_lg_k(14).build();
for(int i = 0; i < 86384; i++) update_sketch3.update(i);
datasketches::theta_union sk_union1 =
datasketches::theta_union::builder().set_lg_k(16).build();
sk_union1.update(update_sketch1);
sk_union1.update(update_sketch2);
sk_union1.update(update_sketch3);
std::cout <<"test2: result1: " << sk_union1.get_result().get_estimate()
<< std::endl;
datasketches::theta_union sk_union2 =
datasketches::theta_union::builder().set_lg_k(16).build();
sk_union2.update(update_sketch1);
sk_union2.update(update_sketch3);
sk_union2.update(update_sketch2);
std::cout <<"test2: result2: " << sk_union2.get_result().get_estimate()
<< std::endl;
the result is :
test2: result1: 151281
test2: result2: 126358
There is a big gap between 151281 and 126358, because of different merge
order：
[update_sketch1 -> update_sketch2 -> update_sketch3]
[update_sketch1 -> update_sketch3 -> update_sketch2]
but I using datasketches-java do the same things, I didn't find any problems.
because I set update_sketch's lg_k = 14 and theta_union‘s lg_k = 16, If
the theta_union‘s lg_k > update_sketch's lg_k there will be a problem, but if
theta_union‘s lg_k <= update_sketch's lg_k there will be no problem.
can we fix this problem?
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