Property MaxMergeMB

Determines the largest segment (measured by total byte size of the segment's files, in MB) that may be merged with other segments. Small values (e.g., less than 50 MB) are best for interactive indexing, as this limits the length of pauses while indexing to a few seconds. Larger values are best for batched indexing and speedier searches.

Note that MaxMergeDocs is also used to check whether a segment is too large for merging (it's either or).