commit fc95c928069537b3f3a6baf86f220b893d42fdc5
author Gian Merlino <gianmerlino@gmail.com> Tue Oct 26 08:05:56 2021 -0700
committer GitHub <noreply@github.com> Tue Oct 26 08:05:56 2021 -0700
tree 87cec1007674c56234ac00383ddf8a9a5a8ab39f
parent 8ea9309168fe0b4e182991d4c71a27467675a769

Remove OffheapIncrementalIndex and clarify aggregator thread-safety needs. (#11124)

* Remove OffheapIncrementalIndex and clarify aggregator thread-safety needs.

This patch does the following:

- Removes OffheapIncrementalIndex.
- Clarifies that Aggregators are required to be thread safe.
- Clarifies that BufferAggregators and VectorAggregators are not
  required to be thread safe.
- Removes thread safety code from some DataSketches aggregators that
  had it. (Not all of them did, and that's OK, because it wasn't necessary
  anyway.)
- Makes enabling "useOffheap" with groupBy v1 an error.

Rationale for removing the offheap incremental index:

- It is only used in one rare scenario: groupBy v1 (which is non-default)
  in "useOffheap" mode (also non-default). So you have to go pretty deep
  into the wilderness to get this code to activate in production. It is
  never used during ingestion.
- Its existence complicates developer efforts to reason about how
  aggregators get used, because the way it uses buffer aggregators is so
  different from how every other query engine uses them.
- It doesn't have meaningful testing.

By the way, I do believe that the given way the offheap incremental index
works, it actually didn't require buffer aggregators to be thread-safe.
It synchronizes on "aggregate" and doesn't call "get" until it has
stopped calling "aggregate". Nevertheless, this is a bother to think about,
and for the above reasons I think it makes sense to remove the code anyway.

* Remove things that are now unused.

* Revert removal of getFloat, getLong, getDouble from BufferAggregator.

* OAK-related warnings, suppressions.

* Unused item suppressions.