Database / RocksDB Basics Interview Questions
What is a Sync Write versus an Async Write in RocksDB?
This distinction is about whether a write waits for its write-ahead log entry to be physically confirmed on durable storage before returning to the caller.
- Sync write: waits for the WAL entry to be flushed all the way to physical storage before the write call returns, guaranteeing durability even against a full power loss
- Async write: returns as soon as the write is applied to memory and the OS's write buffer, without waiting for a physical disk sync, which is faster but risks losing very recent writes on a hard crash
This is a direct trade-off between write latency and durability guarantees, and RocksDB lets applications choose per-write which side of that trade-off they need.
What does a Sync write wait for before returning?
What risk does an Async write accept in exchange for speed?
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