Affects Version/s: Minecraft 14w30c, Minecraft 14w31a, Minecraft 14w32a, Minecraft 14w34c
Fix Version/s: Minecraft 1.8-pre1
Environment:2.54 GHz Intel Core 2 Duo
NVIDIA GeForce 9400M 256 MB
Mac OS X (x86_64) version 10.9.4
Java Version: 1.6.0_65, Apple Inc.
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
Running a single player flat world, I noticed a constant high CPU load (around 140% of core cycles) from minecraft and, indeed, it couldn't keep up 20 TPS. Using the speed of items through a hopper, I measured it to be running at about 7 TPS. Upon pausing the game, the CPU load drops substantially. I used all minimal video settings including 2-chunk render distance. If I bring up the debug profiler pie chart, it changes very little when pausing the game which leads me to believe it's a server-side issue. FPS remains as good as it has always been.
If it helps, I tested the snapshots dichotomically and found that the issue appears in 14w25b.
Also tried with Java 7 and 8 for same results.