Historically it was considered that MySQL will generally use only one index per referenced table in a SQL query. In MySQL 5.0 the introduction of merge indexes enabled for certain conditions the possibility to utilize two indexes however this could result in worst performance then creating a better index. In MySQL 5.1 it became possible to control optimization switches with the optimizer_switch system variable.

However in explaining how to utilize the intersection, union and sort union in queries I discovered that MySQL could use three indexes for one given table.

        Extra: Using union(name,intersect(founded,type)); Using where

I was not aware of this.

Many people consider this information in the MySQL Query Execution Plan (QEP) to indicate that the referenced table is using an index. It actually means that ONLY the index is used. This can for larger and more frequent queries provide a significant boost.

In a recent example, adding an index dropped a query from 190ms to 6ms. However adding a better index dropped that 6ms query to 1.2ms. When executed 100s/1000s of times per second these millisecond improvements can have a huge benefit in greater scalability. While people often tune slow running queries, in a well tuned system shaving milliseconds of queries, in this example making 6ms query 80% better is a far greater improvement.

You can get a detailed explanation of how to identify, create and verify covering indexes from my Percona Live presentation Improving performance …

Hello there, it’s me again, with another blog about a DBA situation that a typical Linux Administrator may find themselves in.

In this blog, i’m going to review a recent MySQL upgrade I have done on one of the systems I am involved in administering. This is a real world example of an upgrade project, and hopefully when we’re done, there may even be an overall performance boost.

There are several reasons to perform upgrades (of any kind), for me an important one is to keep current for security and bug fixes, but general performance improvements and new features are always welcome as well.

This system is running Bacula, an open source enterprise backup system. In this particular case Bacula is configured to store data in a MySQL database. The data stored include status reports, backup content lists, lists of all the files on all the systems, schedules and other related information. While everything has been …

hey man.. thanks…. thanks for u r post…
Its help me…

In December I covered the topic The state of MySQL forks: co-operating without co-operating (which was also a response to Giuseppe Maxia's take on the same topic). Since half a year has now passed, I was wondering if I should follow up with an update. (Drizzle having a GA release would be the major news in such an update.)

But I see that Peter Zaitsev covered this topic in the opening keynote of their Percona Live conference. Since I agree with Peter's view on this topic, I just recommend you watch the talk on Percona.TV. He also uses the same categorizations of the forks, and includes "community patches" as its separate …

I have a Cisco router at home which I also use as a DHCP server, and it works pretty well. Today I wanted to fix a long-standing issue on my network, in that I want multiple DNS search domains.

First off, the domain-name DHCP option doesn’t support multiple entries so we can’t use that.

So, off to try raw DHCP option codes. You can find the list of options here:

http://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xml

thus 119 is the one I want.

Trying a simple:

ip dhcp pool host.net.example.com
   option 119 ascii net.example.com,example.com

didn’t work at all. A quick prod of lazyweb (in this case Simon on IRC) suggested using hex input instead. In order to do that we need to convert the ASCII string into Cisco’s hex sequence, …

One of the best things I find with OS X is the consistent and sane handling of keyboard and mouse bindings. Since having to move back to Linux for work I am constantly frustrated that different applications all have their own idea of what shortcuts to use.

One of the biggest annoyances was the mouse click behaviour in the browser URL bar. OS X behaviour is one click to position cursor, two clicks to select a word, three clicks to select all. I rely on this behaviour a lot as I frequently copy/paste parts of URLs.

Thankfully that’s one that can be fixed easily. Simply navigate to about:config and double click on the browser.urlbar.doubleClickSelectsAll key to set it to false.

One annoyance down, lots more to go..

Reminder: Due to busy summer conference schedules, we are going to be publishing the podcast every other week.

This week we talk about a monitoring plugin from PalominoDB that uses caching (like the cacti templates) and allow for arbitrary calculations of thresholds based on status and system variables, and items from the PROCESSLIST.

Nagios
pnp4nagios - from the site, "PNP is an addon for the Nagios Network Monitoring System. PNP provides easy to use, easy to configure RRDTools based performance charts feeded by the performance data output of the Nagios Plugins."

read …

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In the first part of this entry, it was shown how its possible that a password from a normal user would significantly be weaker than that from a complex and randomly generated one.

Note: in the strictest sense, there is no such thing as an uncrackable password. Passwords can be uncrackable only in theory, i.e. the mathematical probability of a password being guessed correctly-- no matter how infinitesimally small the odds are, the possibility of a right guess is always present. Also, passwords are uncrackable only technically-- given enormous resources and time any password can be cracked.

Here is a function for a truly random and complex password generator which is based on …

If you run Debian or Ubuntu, and want a way to auto-generate a sources.list entry, then you should definitely look at: Setting up Repositories for Ubuntu/Debian. Its very simple: choose a distribution, then a release, then choose what version of MariaDB you would like to track and a mirror of your choice, and voila! it generates the sources.list for you.