Hello, Several companies have made zlib significantly faster by using modern CPU instructions (on the x86-64 arch) – typically, the CRC32 instructions, carryless multiplication (PCLMULQDQ), maybe some window rolling and SSE 4.x instructions. We're having trouble using these zlib forks with nginx because of the hardcoding of the legacy zlib structures. You can see a summary of the issues onby WebDev - Ideas and Feature Requests