How To Measure MySQL Query Performance with mysqlslap

05/11/2017 Categories: Bases de données Tags: , , , Comments off

Introduction

MySQL comes with a handy little diagnostic tool called mysqlslap that’s been around since version 5.1.4. It’s a benchmarking tool that can help DBAs and developers load test their database servers.

mysqlslap can emulate a large number of client connections hitting the database server at the same time. The load testing parameters are fully configurable and the results from different test runs can be used to fine-tune database design or hardware resources.

In this tutorial we will learn how to use mysqlslap to load test a MySQL database with some basic queries and see how benchmarking can help us fine-tune those queries. After some basic demonstrations, we will run through a fairly realistic test scenario where we create a copy of an existing database for testing, glean queries from a log, and run the test from a script.

The commands, packages, and files shown in this tutorial were tested on CentOS 7. The concepts remain the same for other distributions. Lire la suite…

How do I… Stress test MySQL with mysqlslap?

04/11/2017 Categories: Bases de données Tags: , , , Comments off

One of the interesting new tools in MySQL 5.1.4 is mysqlslap, a load emulator that lets you see how well a particular query set or table engine performs under high-load conditions.

A query that consumes too many database resources may be the result of designing tables incorrectly, choosing the wrong table type, or creating an inefficient query. When a query eats up a lot of database resources, it can negatively affect other application components. By using mysqlslap to stress test a server in a non-public environment, you will discover these errors sooner, allowing you to you avoid a database meltdown once your application goes live.

This tutorial shows how you can use mysqlslap to run stress tests involving multiple clients, custom queries, different table engines, and much more. Lire la suite…

ORC – Un réseau de stockage cloud, anonyme et décentralisé reposant sur Tor

02/11/2017 Categories: Logiciel, Sécurité, Système Tags: Comments off

Counterpoint Hackerspace, une bande de geeks localisée à Roswell dans l’état de Georgie aux États unis, a eu l’excellente idée de mettre au point un outil permettant de stocker sur Tor des fichiers, un peu à la manière d’un espace « cloud », mais avec tous les avantages que Tor peut apporter : anonymat, décentralisation et gestion par la communauté. Lire la suite…

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High Sierra Problems: How To Fix The Most Common Macos Issues

30/10/2017 Categories: Logiciel, Système Tags: , Comments off

The excitement of installing a new version of macOS, especially if its a High Sierra 10.13, is only tempered by the possibility of it not working properly or not being compatible with the apps you use most.

Before you begin upgrade to MacOS make a bootable backup

If you haven’t started the process of upgrading yet, check if the Mac is compatible with macOS High Sierra and make a bootable backup. 

Do it now, before you do anything else. If things go disastrously wrong at least you’ll be able to boot from macOS’ Recovery partition and migrate all your data back to your Mac. You can use any backup tool you like – Apple obviously favours Time Machine, but you don’t have to use it. You can use, for example, Get Backup Pro, which comes with your Setapp subscription. Don’t have a Setapp subscription? Click here to sign up.

Common MacOS High Sierra Problems

While most new versions of macOS are relatively problem-free, it’s not unknown for users to have issues – particularly with a beta or .0 release. Thankfully most are easy to resolve. Here’s how to fix the most common High Sierra issues.

High Sierra Installer Won’t Download

If you’re trying to download the macOS High Sierra installer, you’ll need to have signed up to App Store. If you’ve done that, and managed to start the downloading process only for it to fail, force quit the App Store app.

  1. Press Cmd-Alt-Esc or go to the Apple menu and choose Force Quit.
  2. Select the App Store app and confirm you want to force quit.
  3. Re-launch the App Store and try downloading again.

Macos High Sierra Won’t Install

If the download completes successfully but the installation doesn’t finish, force quit the installer using the same procedure as above. 

  1. Restart your Mac
  2. Launch the App Store app and go to the Purchases tab. 
  3. Find macOS High Sierra and click Install. 

If that doesn’t work, try deleting the downloaded installer (it’s in your Applications folder) using CleanMyMac and download it again.

If you have a copy of macOS Server in your applications folder, that may be the root of the problem. Delete it and try again.

Lire la suite…

Categories: Logiciel, Système Tags: ,

If your iPhone, iPad, or iPod touch won‘t turn on or is frozen

30/10/2017 Categories: Constructeur, Matériel Tags: , Comments off

If your device has a frozen screen or doesn’t respond when you touch it, or becomes stuck when you turn it on, learn what to do.

If your screen is black or frozen

If your screen is black or frozen, you might need to force restart your device. A force restart won’t erase the content on your device. You can force restart your device even if the screen is black or the buttons aren’t responding. Follow these steps:

  • On an iPhone 8 or iPhone 8 Plus: Press and quickly release the Volume Up button. Then press and quickly release the Volume Down button. Finally, press and hold the Side button until you see the Apple logo.
  • On an iPhone 7 or iPhone 7 Plus: Press and hold both the Side and Volume Down buttons for at least 10 seconds, until you see the Apple logo.
  • On an iPhone 6s and earlier, iPad, or iPod touch: Press and hold both the Home and the Top (or Side) buttons for at least 10 seconds, until you see the Apple logo.

If your device still won’t turn on or start up

Plug in your device and let it charge for up to one hour.

After a few minutes, you should see the charging screen. 

 

If you don’t see the charging screen within an hour, or you see the connect to power screen, check the jack, USB cable, and power adapter. Make sure that everything is plugged in firmly, free of debris, and not damaged. You might want to try a different USB cable or power adapter.

If your device still doesn’t turn on, see what to do next.

If your device turns on but gets stuck during start up

If you see the Apple logo or a red or blue screen during startup, try these steps:

  1. Connect your device to a computer and open iTunes. If you don’t have a computer, try to borrow one, or go to an Apple Store or Apple Authorized Service Provider for help. 
  2. While your device is connected, force it to restart. 
    • On an iPhone 8 or iPhone 8 Plus: Press and quickly release the Volume Up button. Then press and quickly release the Volume Down button. Finally, press and hold the Side button until you see the recovery-mode screen.
    • On an iPhone 7 or iPhone 7 Plus: Press and hold the Side and Volume Down buttons at the same time. Keep holding them until you see the recovery-mode screen.
    • On an iPhone 6s and earlier, iPad, or iPod touch: Press and hold both the Home and the Top (or Side) buttons at the same time. Keep holding them until you see the recovery-mode screen.
  3. Don’t release the buttons when you see the Apple logo. Keep holding until you see the recovery mode screen.

 

  1. When you get the option to restore or update, choose Update. iTunes will try to reinstall iOS without erasing your data.

iTunes will download the software for your device. If it takes more than 15 minutes, your device will exit recovery mode and you’ll need to repeat steps 2 and 3.

 
Categories: Constructeur, Matériel Tags: ,