Database / RocksDB Basics Interview Questions
Define Leveled Compaction?
Leveled compaction organizes SSTables into a series of levels, L0 through Ln, where each level is typically several times larger than the one above it.
- Level 0 holds SSTables flushed directly from MemTables, and their key ranges may overlap
- From Level 1 onward, SSTables within a level cover non-overlapping key ranges, kept strictly sorted
- When a level exceeds its size limit, some of its SSTables are merged into the level below, gradually pushing data downward over time
This structure keeps reads efficient, since only a bounded number of SSTables per level need to be checked, at the cost of some write amplification from the repeated merging.
Do SSTables within Level 0 typically have overlapping key ranges?
What happens when a level exceeds its size limit?
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