Compaction Overhead Calculator

Work out compaction overhead instantly with clear inputs, formula shown and shareable results.

About Compaction Overhead Calculator

Compaction consumes the amplified portion of write traffic, so at seven times amplification it uses six times the ingest rate in background I/O. Adding that to the foreground writes gives total disk demand, and when it approaches the device limit compaction falls behind: SSTable counts grow, read amplification rises and latency degrades even though ingest looks fine.

Formula

Compaction load

compaction throughput = ingest x (amplification - 1); total disk = ingest x amplification; utilisation = total / device throughput

Worked example

With the default values below, Compaction Overhead Calculator returns Throughput consumed by compaction of 150.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Ingest rateminimum 0.001 MB/s: 25 MB/s
Write amplification factoraccepts 1–50 x: 7 x
Available disk throughputminimum 1 MB/s: 400 MB/s
Compaction threadsaccepts 1–64: 4

Results

Throughput consumed by compaction: 150.00 MB/s
Disk throughput utilisation: 43.8%
Compaction throughput per thread: 37.50 MB/s
Assessment: Comfortable headroom

Step by step

1Values used
2Compaction load
3Throughput consumed by compaction= 150.00 MB/s
4Disk throughput utilisation= 43.8
5Compaction throughput per thread= 37.50 MB/s
6Assessment= Comfortable headroom

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What happens when compaction cannot keep up?

Pending compactions accumulate, each read must consult more files, and eventually the engine applies backpressure or stalls writes entirely.

Should compaction be throttled?

Throttling protects foreground latency in the short term but guarantees a backlog if the amplified rate genuinely exceeds the device. The real fix is faster storage or lower amplification.