What is compaction in the database? Think of your disks as a warehouse: The compaction mechanism is like a team of storekeepers (with genius organizing skills like Marie Kondo) who help put away the incoming data.
In particular, the data (which is the inflowing cargo in this metaphor) comes in on a “conveyor belt,” which does not allow cutting in line. This is how the LSM-Tree (Log Structured-Merge Tree) works: In data storage, data is written into MemTables in an append-only manner, and then the MemTables are flushed to disks to form files. (These files go by different names in different databases. In my community, we call them Rowsets). Just like putting small boxes of cargo into a large container, compaction means merging multiple small rowset files into a big one, but it does much more than that. As I said, the compaction mechanism is an organizing magician: