stefanvodita commented on PR #12966: URL: https://github.com/apache/lucene/pull/12966#issuecomment-1890420916
I found a fun HeisenBug in one of the tests. When we iterate cursors from `IntFloatHashMap`, the order is not deterministic. Float summation is not commutative, so the result we get by aggregating the floats in the map can be different depending on the order in which we perform the iteration. For a particular seed, running the test was producing an ordering that was not favorable, while running the debugger produced an ordering that was. The test is fixed in the latest commit and I've opened an [issue to do Kahan summation](https://github.com/apache/lucene/issues/13011) over the floats instead, to reduce the error we're seeing. For those who want to follow along, here are the exact numbers we are adding in the test in two orderings which produce different results: ``` class FloatSunIsNotCommutative { public static void main(String[] args) { float x = 177182.61f; float y = 238089.27f; float z = 255214.66f; float acc; acc = 0; acc += x; acc += y; acc += z; System.out.println(acc); acc = 0; acc += z; acc += y; acc += x; System.out.println(acc); } } ``` -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: issues-unsubscr...@lucene.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@lucene.apache.org For additional commands, e-mail: issues-h...@lucene.apache.org
