Facebook’s Caching Architecture Facebook operates two distinct caching systems, each designed for different access patterns and consistency requirements. Memcache serves as a lookaside cache where the intelligence resides primarily on the client side. This architecture means applications are responsible for cache invalidation, consistency checks, and determining what data to cache. Memcache is stateless and horizontally…
Diagnosing High TCP Retransmission Rates in Virtual Machines If you’re seeing elevated TCP segment retransmission counts on Xen VMs, this typically signals network congestion, packet loss, or CPU contention. Here’s how to identify the root cause and fix it. Check Your Current Retransmission Rate Start by gathering baseline metrics: ss -s Look for the retransmit…
Force Page Refresh and Cache Invalidation in Chrome for iOS Chrome on iOS implements aggressive caching to improve browsing performance, but this can prevent you from seeing the latest versions of pages, stylesheets, and scripts. Unlike Safari’s convenient long-press refresh button, Chrome’s cache management is less intuitive. The Nuclear Option: Clear All Cache The most…
Installing Scala from the official distribution When your distro’s package repositories lag behind, installing Scala directly from the official release is straightforward. This approach works on any Linux system with Java already installed. Prerequisites You’ll need a JDK installed. On most systems: # Debian/Ubuntu apt install default-jdk # RHEL/Fedora/CentOS dnf install java-17-openjdk-devel # Alpine apk…
Excluding repositories in dnf/yum You’ll sometimes need to exclude specific repositories from package operations—typically when multiple repos provide the same package, mirror connectivity is unreliable, or you want to force installation from a trusted source. The –disablerepo flag lets you skip repos on a per-command basis. Basic syntax dnf –disablerepo=repoid1 –disablerepo=repoid2 install package-name Add –disablerepo…
Install Java Scala runs on the JVM, so you need Java installed first. Install the default JDK with: sudo dnf install java-latest-openjdk java-latest-openjdk-devel On Fedora, this installs OpenJDK to /usr/lib/jvm/java-*-openjdk-* and symlinks it as /usr/lib/jvm/java. Verify the installation: java -version javac -version Install Scala Scala is available in the Fedora repository. Install it with: sudo…
Customizing Question2Answer RSS feeds to show excerpts Question2Answer’s RSS feed configuration includes a toggle for “Include full text in feeds” but offers no built-in option to display excerpts instead of full content. If you need excerpt functionality, you’ll need to modify the feed generation code. This approach works with Question2Answer 1.5.4+. The method involves creating…
Removing All Posts and Topics from a Spammer in MyBB If you need to clean up spam content across your MyBB forum quickly, the Goodbye Spammer plugin automates the process of banning a user and removing all their content in one operation. Installation Download the Goodbye Spammer plugin from the MyBB Mods site, then: Upload…
Getting Assembly Code from OCamlopt To generate native assembly code (x86-64 asm, ARM64, etc.) from OCaml’s native compiler, use the -S flag along with other optimization-related options: ocamlopt -S -inline 20 -nodynlink not.ml -o not.opt This produces a .s file containing the generated assembly. The flags break down as: -S — Stop after assembly generation…
Storage of routing table entries Linux routing tables exist in kernel memory during runtime. To persist routes across reboots, you need to store them on disk and have them reloaded during system startup. The mechanism varies depending on your network management setup. systemd-networkd and netplan (modern systems) On contemporary distributions using systemd-networkd or netplan, define…
Understanding the Content-Type Issue When you pipe a plain text file to mailx, it analyzes the content to determine the MIME type. If it detects non-standard characters (anything other than newlines and horizontal tabs), it defaults to application/octet-stream and base64-encodes the message. Most email clients then treat this as an attachment rather than inline content….
MySQL Table Corruption: Detection and Repair A MySQL table marked as crashed typically occurs after unclean shutdowns, power failures, or server crashes. Error 145 indicates the table structure is corrupted and needs repair before queries can proceed. Checking Table Status Before attempting repair, check the table status: CHECK TABLE mybb_sessions; This returns detailed information about…
Listing Remote Branches in Git Local branches List all branches on your local repository: git branch This shows only branches that exist locally on your machine. Remote branches To list all branches on the remote server, use the -r flag: git branch -r This displays remote-tracking branches — local references to branches that exist on…
Using OCaml as a Scripting Language You can run OCaml scripts directly from the command line with a shebang, similar to bash or Python. This requires making the file executable and using the proper interpreter directive. Basic Script Setup Create a file with a .ml extension and add a shebang at the top: #!/usr/bin/env ocaml…
Saving Word Documents as PDF Converting Word documents to PDF is a fundamental task in most workflows. Modern versions of Office have native PDF export built in, but understanding your options and potential gotchas will save you time. Native PDF Export (Modern Office) If you’re using Office 2010 or later, PDF export is built into…
Printing Web Pages Effectively Copying webpage content directly into a document often produces poor formatting, missing images, or broken layouts. Here are several practical approaches to get clean, readable output. Browser Print Dialog (Native) Most modern browsers have built-in print functionality that’s worth trying first: Open the page in your browser Press Ctrl+P (Linux/Windows) or…
iTunes Backup Locations iTunes backups are stored in device-specific directories. The location depends on your operating system: macOS: ~/Library/Application Support/MobileSync/Backup/ Windows: %APPDATA%\Apple Computer\MobileSync\Backup\ On Windows, the easiest way to navigate there is to press Win + R, type %appdata% and hit Enter, then navigate to Apple Computer\MobileSync\Backup\. Understanding iTunes Backup Files iTunes stores backups as…
Adjusting Y-Axis Label Position in Gnuplot Y-axis labels in Gnuplot can end up positioned awkwardly depending on your terminal, font, and tick label width. The most straightforward solution is using the offset option in the set ylabel command. Basic Offset Syntax The offset takes three parameters: horizontal, vertical, and depth (for 3D plots): set ylabel…
Controlling Font Sizes in Gnuplot Font sizes in Gnuplot plots often appear too small when scaling images down for papers or presentations. You can control font sizes at multiple levels: globally for the terminal, for axis labels and tick marks, for legends, and for individual text elements. Global Terminal Font Size Set a default font…
Setting Up Chrome RSS Subscription Extension with Feedly If you use both the Chrome RSS Subscription Extension and Feedly, you can integrate them so that clicking the RSS icon in your browser automatically opens your feed in Feedly instead of the browser’s default handler. Understanding the Integration When you subscribe to an RSS feed through…