Model

When compression speeds up a read

A ratio above ~4× buys you almost nothing on the read path. Everyone chases ratio. The derivation says: chase decode speed.

\frac{S}{r B} + \frac{S}{D} < \frac{S}{B} ⟺ \frac{D}{B} > \frac{r}{r - 1}

$B$: Pipe bandwidth; the bandwidth of the pipe the data travels through (disk or network)
$r$: Ratio; the compression ratio
$D$: Decode throughput; the decode throughput, measured in output bytes per second
$S$: Size; bytes read, uncompressed

How it behaves

One input on the horizontal axis, the others held fixed.

Data table

How much faster than the pipe the decoder must be, by compression ratio
Compression ratio r	Decode speed ÷ pipe speed, at least
1.1	11×
1.14	8.28×
1.18	6.68×
1.22	5.63×
1.26	4.88×
1.3	4.33×
1.34	3.9×
1.39	3.56×
1.44	3.28×
1.49	3.05×
1.54	2.86×
1.59	2.7×
1.64	2.55×
1.7	2.43×
1.76	2.32×
1.82	2.22×
1.88	2.14×
1.94	2.06×
2.01	1.99×
2.08	1.93×
2.15	1.87×
2.22	1.82×
2.3	1.77×
2.38	1.73×
2.46	1.69×
2.54	1.65×
2.63	1.62×
2.72	1.58×
2.81	1.55×
2.9	1.53×
3	1.5×
3.1	1.48×
3.21	1.45×
3.32	1.43×
3.43	1.41×
3.55	1.39×
3.67	1.37×
3.79	1.36×
3.92	1.34×
4.06	1.33×
4.2	1.31×
4.34	1.3×
4.49	1.29×
4.64	1.27×
4.8	1.26×
4.96	1.25×
5.13	1.24×
5.3	1.23×
5.48	1.22×
5.67	1.21×
5.86	1.21×
6.06	1.2×
6.27	1.19×
6.48	1.18×
6.7	1.18×
6.93	1.17×
7.17	1.16×
7.41	1.16×
7.66	1.15×
7.92	1.14×
8.19	1.14×
8.47	1.13×
8.76	1.13×
9.06	1.12×
9.37	1.12×
9.69	1.12×
10	1.11×
10.4	1.11×
10.7	1.1×
11.1	1.1×
11.4	1.1×
11.8	1.09×
12.2	1.09×
12.7	1.09×
13.1	1.08×
13.5	1.08×
14	1.08×
14.5	1.07×
15	1.07×
15.5	1.07×
16	1.07×

Every number the mechanisms quote for this relationship is recomputed from it, so none of them disagrees with it.

Each mechanism states it in its own names. The general symbol each name stands for is shown with it.

Encoding, Serialization & Compression
What do we turn our values into when we turn them into bytes, and what does that choice cost?
$D / B > r / (r - 1)$
Read it in place →
Execution Engine Runtime
Once a query plan is chosen, why does the machine still sit idle, and what does each mechanism of a query runtime pay to buy that idle time back?
$C > B W \cdot \frac{r}{r - 1}$
C (codec speed) = $D$ · BW (link) = $B$
Read it in place →