Help: why the LF index size increased so big?

hi guys,

     I got a issue, that a LF typed index increased so big.

     I have a table with a TIME column to store HH:mm:ss, and in fact, the value for this column is aligned with 5 minute (only 00:00:00, 00:05:00, 00:10:00, etc. will be saved in this column). thus, there are ONLY 288 unique values. and I use LF typed index.

     there are about 15 billion data in this table, and if rebuild the LF index, the size will be ~24G. but after the new data inserted, the size of this LF index will increased so much. I got 200G after some days. and when delete and rebuild this index, i return to ~24G.

     what's happens? and how to prevent this happen?

PS: I use IQ 16.0 SP8.