flushNextBuffer

Expert: Flushes the next pending writer per thread buffer if available or the largest active non-pending writer per thread buffer in the calling thread. This can be used to flush documents to disk outside of an indexing thread. In contrast to .flush this won't mark all currently active indexing buffers as flush-pending.

Note: this method is best-effort and might not flush any segments to disk. If there is a full flush happening concurrently multiple segments might have been flushed. Users of this API can access the IndexWriters current memory consumption via .ramBytesUsed