Jackie-Jiang commented on pull request #7076:
URL: https://github.com/apache/incubator-pinot/pull/7076#issuecomment-865252385
@tdunning
The random t-digest objects are created as following:
```
@Override
Object getRandomRawValue(Random random) {
TDigest tDigest = TDigest.createMergingDigest(COMPRESSION);
tDigest.add(random.nextInt(MAX_VALUE));
tDigest.add(random.nextInt(MAX_VALUE));
return ObjectSerDeUtils.TDIGEST_SER_DE.serialize(tDigest);
}
```
In non-star-tree approach simply merges the t-digests in sequence without
ser-de; the star-tree approach will pre-aggregate t-digests and then stores the
serialized merged t-digests (each pre-aggregated t-digest might go through
multiple rounds of ser-de).
Non-star-tree:
```
TDigest tDigest = deserialize(tDigest1);
tDigest.add(deserialize(tDigest2));
tDigest.add(deserialize(tDigest3));
tDigest.add(deserialize(tDigest4));
```
Star-tree:
```
TDigest tDigest = deserialize(tDigest1);
tDigest.add(deserialize(tDigest2));
byte[] mergedTDigest1 = serialize(tDigest);
tDigest = deserialize(tDigest3);
tDigest.add(deserialize(tDigest4));
byte[] mergedTDigest2 = serialize(tDigest);
tDigest = deserialize(mergedTDigest1);
tDigest.add(deserialize(mergedTDigest2));
```
Then we compare the result for each quantile from these 2 result t-digest
objects.
Hope this can explain the test logic.
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