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TL;DR Modern disks are so fast that system performance bottleneck shifts to RAM access and CPU. With up to 64 cores, PCIe 4.0 and 8 memory channels, even a single-socket AMD ThreadRipper Pro workstation makes a hell of a powerful machine - if you do it right! Update 1: Since 2021, networks have gotten faster and now…
Here’s a list of reasons why SELECT * is bad for SQL performance, assuming that your application doesn’t actually need all the columns. When I write production code, I explicitly specify the columns of interest in the select-list (projection), not only for performance reasons, but also for application reliability…
Over the years of troubleshooting performance problems in the Unix/Linux world, I have seen multiple cases where a regularly used command line tool in a customer server just stops working for some reason. The tool just returns immediately, doing absolutely nothing. No output printed, no coredumps and the exit code is…
TL;DR: Some Linux distros and even different kernel versions within a distro have disabled IRQ time accounting. In such case, your monitoring tools will report zero time spent in hardware interrupt handlers (shown as %hi, %irq, hiq, etc). It’s easy to check how your kernel is behaving by looking at /proc/stat and you…
Starting from v8.0.27, the MySQL daemon shows its thread names at the OS level too, for better troubleshooting. The MySQL 8.0.27 release notes say this: To assist monitoring and troubleshooting, the Performance Schema instrumentation is now used to export names of instrumented threads to the operating system. This…
As my cat woke me up way too early for a Saturday morning, I decided to put all this extra time (and my ChatGPT Pro subscription) into good use and generated a QR-code generator for PostgreSQL, written as a single pure SQL statement. No external libraries or Postgres extension installation needed! The pqr.sql example…
TLDR; Starting from Linux kernel version 6.9 on x86_64, there’s a new config option CONFIG_X86_FRED enabled and it adds 16 bytes to the starting point of a task’s kernel stack area, so you’ll need to account for this extra padding in your “raw” kernel stack & pt_regs lookup code. Update: It turns out that there’s a…
When dealing with disks and I/O things on Linux, you’d regularly run commands like lsblk, lsscsi, nvme list, etc. All of them tend to report a different set of information, so I ended up running multiple commands and correlating their output based on the device name or number. And then I had to run commands like…