Merge index segments (force merge)

Command

POST /customer/_forcemerge?max_num_segments=1

What it does

Merges index segments to reduce the segment count and improve read performance.

When to use it

Only on indices that are no longer written to (read-only), to improve query performance.

Caution

Consumes heavy IO and CPU; never run it on actively written indices. It can take a long time and cannot be cancelled.