Reuse buffers while querying vector indexes

[CascadingRadium]

• Currently we allocate 2 buffers of size K for every segment available in the snapshot. In a 'full-flow' indexing scenario, we can have a large number of segments, so for each query incident on the index, we allocate a total space of S = numSegments * K * 12 Bytes. Although the semaphore prevents S from being allocated instantaneously, the total space will still be allocated and GC'd, leaving behind a large memory footprint for every query. With this approach, the space allocated per query is S' = min(10, numSegments) * K * 12 Bytes which drastically reduces the memory footprint left behind per query as it becomes independent of the number of segments available in the system

• i know this breaks interfaces; if it is bad, I will close the pull requests associated with this

• please let me know what you think about this