As discussed in a recent mailing list thread  and observed in a project using Lucene (see
OAK-5192 and OAK-6710), it is sometimes helpful to throttle the aggressiveness of (Tiered)MergePolicy when commit rate is high.
In the case of Apache Jackrabbit Oak a dedicated MergePolicy was implemented .
That MP doesn't merge in case the number of segments is below a certain threshold (e.g. 30) and commit rate (docs per sec and MB per sec) is high (e.g. above 1000 doc / sec , 5MB / sec).
In such impl, the commit rate thresholds adapt to average commit rate by means of single exponential smoothing.
The results in that specific case looked encouraging as it brought a 5% perf improvement in querying and ~10% reduced IO. However Oak has some specifics which might not fit in other scenarios. Anyway it could be interesting to see how this behaves in plain Lucene scenario.