blktrace analysis of MySQL doublewrite buffer contention

InnoDB dirty page flush stalling on NVMe I/O queues Background Observation A background image processing task was causing a 4.5-second I/O stall on the database layer. The web nodes run Henrik - Creative Magazine WordPress Theme , which generates heavily stylized image grids. When content editors uploaded high-resolution TIFF files, a PHP CLI daemon triggered ImageMagick to generate multiple WebP derivatives. During this specific image generation phase, the MySQL database running on the same physical NVMe storage array exhibited severe latency on UPDATE queries. CPU wait time ( %iowait ) spiked from 0.1% to 14%. Memory was not exhausted. Swap was disabled. Network interfaces were idle. The issue was strictly confined to the block I/O layer and how MySQL's storage engine interacted with the underlying filesystem during rapid metadata writes. I/O Latency Profiling I began by observing the block device metrics using iostat at one-second intervals to capture the precise window of the stall