Null handling bitmap performance

[gianm]

I noticed that the null bitmap checks from #5278 are usually implemented like:

        public boolean isNull()
        {
          return nullValueBitmap.get(offset.getOffset());
        }

From what I recall, get on compressed bitmaps can be quite slow compared to walking an iterator.

[stale]

This issue has been marked as stale due to 280 days of inactivity. It will be closed in 2 weeks if no further activity occurs. If this issue is still relevant, please simply write any comment. Even if closed, you can still revive the issue at any time or discuss it on the dev@druid.apache.org list. Thank you for your contributions.

[gianm]

I believe this is still relevant.

[stale]

This issue is no longer marked as stale.

[b-slim]

@gianm any idea why a get with an offset is more expensive than walking iterator ?

[gianm]

@b-slim I'm not familiar with their implementation enough to know, but I could speculate. Perhaps the compressed bitmap iterators cache some information that needs to be re-computed if you are calling get repeatedly.

[gianm]

Fixed by #8822.