Daniel Lemire

Implement reverse batched iterators

7

Generalize Richard's bulk iterators so we can iterate backward (in reverse)... https://github.com/RoaringBitmap/RoaringBitmap/pull/243 See: Iterating in batches over data structures can be much faster... https://lemire.me/blog/2018/04/17/iterating-in-batches-over-data-structures-can-be-much-faster/

Implement flyweight iterators in batch mode

4

We have fast bulk iterators... See PR https://github.com/RoaringBitmap/RoaringBitmap/pull/243 We'd like to support them using the flyweight model.

Parallelize

18

Roaring is ideally suited for parallel execution, as all containers can be operated upon in distinct threads.

Should we benchmark off-heap bitmaps?

2

We do benchmark and test off-heap bitmaps in some specific benchmarks: https://github.com/RoaringBitmap/RoaringBitmap/blob/11fc14b27b674fbb721104630812af248dc75b02/jmh/src/main/java/org/roaringbitmap/BasicBenchmark.java However, it used to be that it was the way we tested all immutable roaring bitmaps. Then we...

Optimize iterators over mapped bitmaps

24

Currently, when iterating over an ImmutableRoaringBitmap, one instantiates object containers and then iterator objects. We could streamline this process by _not_ creating the object containers and iterating directly over the...

Implement partially mapped bitmaps: hybrid Java heap + off heap

26

This is an issue raised by @kishoreg and related to how [Pinot](https://github.com/linkedin/pinot/wiki) uses Roaring bitmaps. Currently, we support ``ImmutableRoaringBitmap``... ``MutableRoaringBitmap`` and ``RoaringBitmap``. The ``ImmutableRoaringBitmap`` class stores the containers off-heap (possibly...

Experiment with DEFAULT_INIT_SIZE = 0 (null arrays) to avoid unnecessary garbage collection

2

When creating array and run containers, we often allocate a Java array having a default size. It is common in some settings that this newly created array will immediately need...

Implement "mutable" memory-mapped bitmaps through copy-on-write

2

Currently, we can map a Roaring bitmap to a disk or out-of-Java storage. ``` ByteBuffer bb = ... ImmutableRoaringBitmap rr = new ImmutableRoaringBitmap(bb); ``` This is great and it works...

Currently, iterators are "read only". Implement the remove method along with the needed tests.

streamline the implementations of iterators to drastically reduce memory allocation

9

Currently, iterators are implemented by instantiating sub-iterators that run over the containers. This approach requires us to create many more temporary objects than necessary. A much simpler approach is the...