The Backend Engineering Show with Hussein Nasser

Dive into the intriguing world of timeouts in programming! Discover how they manage waiting periods, free up resources, and even fend off potential DOS attacks. Learn about different types of timeouts like connection and response, and their broader applications beyond just request processing. Engaging discussions highlight best practices for optimizing client-server interactions and ensuring efficient request handling. Prepare for unexpected insights that could change how you think about frontend and backend communications!

Learn more about database and OS internals, check out my courses  Fundamentals of database engineering https://databases.win  Fundamentals of operating systems https://oscourse.win This new PostgreSQL 17 feature is game changer. You see, postgres like most databases work with fixed size pages. Pretty much everything is in this format, indexes, table data, etc. Those pages are 8K in size, each page will have the rows, or index tuples and a fixed header. The pages are just bytes in files and they are read and cached in the buffer pool. To read page 0, for example, you would call read on offset 0 for 8192 bytes, To read page 1 that is another read system call from offset 8193 for 8192, page 7 is offset 57,345 for 8192 and so on.  If table is 100 pages stored a file, to do a full table scan, we would be making 100 system calls, each system call had an overhead (I talk about all of that in my OS course).  The enhancement in Postgres 17 is to combine I/Os you can specify how much IO to combine, so technically while possible you can scan that entire table in one system call doesn’t mean its always a good idea of course and Ill talk about that.  This also seems to included a vectorized I/O, with preadv system call which takes an array of offsets and lengths for random reads.  The challenge will become how to not read too much, say I’m doing a seq scan to find something, I read page 0 and found it and quit I don’t need to read any more pages. With this feature I might read 10 pages in one I/O and pull all its content, put in shared buffers only to find my result in the first page (essentially wasting disk bandwidth, memory etc)  It is going to be interesting to balance this out. 

Fundamentals of Operating Systems Course https://os.husseinnasser.com Why Windows Kernel connects slower than Linux I explore the behavior of TCP/IP stack in Windows kernel when it receives a RST from the backend server especially when the host is available but the port we are trying to connect to is not. This behavior is exacerbated by having both IPv6 and IPv4 and if the happy eye ball protocol is in place where IPv6 is favorable. 0:00 Intro 0:30 Fundamentals TCP/IP 3:00 Unreachable Port Behavior 6:00 Client Kernel Behavior (Linux vs Windows) 11:40 Slow TCP Connect on Windows 15:00 localhost, IPv6 and IPv4 20:00 Happy Eyeballs 28:00 Registry keys to change the behavior 31:00 Port Unreachable vs Host Unreachable https://daniel.haxx.se/blog/2024/08/14/slow-tcp-connect-on-windows/

In this episode of the backend engineering show I describe an interesting bug I ran into where the web server ran out of ephemeral ports causing the system to halt.  0:00 Intro 0:30 System architecture  2:20 The behavior of the bug 4:00 Backend Troubleshooting 7:00 The cause 15:30 Ephemeral ports on loopback

Linux I/O expert Jens Axboe discusses IO_uring updates for Linux 6.10, focusing on zerocopy. Topics include how normal copying works, zero copy benefits in data transfer, and challenges of SSL/TLS encryption. Explore advancements in kernel technology for efficient data handling.

Fundamentals of Operating Systems Course https://oscourse.win Looks like fedora is compiling cpython with the -o3 flag, which does aggressive function inlining among other optimizations. This seems to improve python benchmarks performance by at most 1.16x at a cost of an extra 3MB in binary size (text segment). Although it does seem to slow down some benchmarks as well though not significantly. O1 - local register allocation, subexpression elimination O2 - Function inlining only small functions O3 - Agressive inlining, SMID 0:00 Intro 1:00 Fedora Linux gets Fast Python 5:40 What is Compiling? 9:00 Compiling with No Optimization 12:10 Compiling with -O1 15:30 Compiling with -O2 20:00 Compiling with -O3 23:20 Showing Numbers Backend Troubleshooting Course https://performance.husseinnasser.com

Allegro improved Kafka latency by 80% switching from ext4 to XFS. They traced Kafka protocol and kernel system calls, optimized ext4 before switching. Show explores file system complexities, journaling impact, and challenges of workload increase.

Get my backend course https://backend.win Google submitted a patch to Linux Kernel 6.8 to improve TCP performance by 40%, this is done via rearranging the tcp structures for better cpu cache lines, I explore this here. 0:00 Intro 0:30 Google improves Linux Kernel TCP by 40% 1:40 How CPU Cache Line Works 6:45 Reviewing the Google Patch https://www.phoronix.com/news/Linux-6.8-Networking https://lore.kernel.org/netdev/20231129072756.3684495-1-lixiaoyan@google.com/ Discovering Backend Bottlenecks: Unlocking Peak Performance https://performance.husseinnasser.com

Exploring torn pages in databases, including Oracle and MySQL solutions. Comparison of file system block and database pages. Postgres full page writes.

Cloudflare's release of Pingora, a networking framework, is a game-changer in the industry. Discussion revolves around its security features, multi-threading capabilities, and the balance between customization and configuration. The move towards Rust for network services marks a significant shift for Cloudflare.