Hardware Tutorials

Installing MongoDB on CentOS 6

Chris — Sun, 19 Feb 2012 22:18:41 +0000

I would have written a guide on how I did this, but the blog post over on If Not True Then False covers it perfectly, so just go over there and follow their guide.

Saving files in memory

Chris — Thu, 16 Feb 2012 11:13:30 +0000

If you need super quick access to a file, for example a log file which isn’t going to be too big but it being used by a script which is time critical, then rather than writing it to disk, you can mount part of your file system in memory and write to it there.

This has the disadvantage that when you restart your system, you will lose the data. But for test scripts, logs or other temporary files that you don’t mind getting lost, it can really speed up performance.

Luckily, most systems come with a an area mounted in memory already – so you don’t even need to configure it!

cd /dev/shm

If said directory exists, you’ll have a memory mounted directory already and can start using it immediately.

Editing your hosts file

Chris — Fri, 10 Feb 2012 11:10:31 +0000

If you want to put custom entries in your computer’s DNS (for running addresses for a local server for example) you need to edit your system’s hosts file. On Unix systems this can be found at:

/etc/hosts

On Windows systems, you need to go to:

C:\Windows\system32\drivers\etc\hosts

To add a custom entry, first enter the IP address (if you’re running a local server you’ll want to set this as 127.0.0.1), then put a tab and then the host name.

Using TextEdit as a text editor

Chris — Sat, 04 Feb 2012 11:09:15 +0000

One utility Mac OS X seems to be lacking is a simple text editor such as Notepad for Windows. It comes with TextEdit but the problem is that this uses rich text format (RTF) which is very annoying when editing system files or code.

Thankfully, you can reconfigure it to use plain text.

Simply go to TextEdit on the menu bar and hit Preferences. The top option should allow you to toggle between Plain Text and Rich Text.

Get the system time from the terminal

Chris — Mon, 30 Jan 2012 11:08:24 +0000

Wondering what your system date/time is? Easy!

date

It’s that obvious . Don’t mistake it with the command “time”, which won’t return you what you want.

i386 or x86_64 architecture?

Chris — Tue, 24 Jan 2012 11:07:04 +0000

Wondering if you’re running i386 or x84_64? No problem, there is quick command which will return this information to you.

uname -i

Profiling SQL queries with EXPLAIN

Chris — Wed, 18 Jan 2012 11:06:02 +0000

If you have a complex SQL query, you might find that performance isn’t exactly ideal. Worse still, you don’t actually know which part of the query it is that is actually taking so long.

Luckily, MySQL comes to the rescue with the ability to explain.

All you have to do is start your query with the keyword EXPLAIN and MySQL will, rather than returning you a recordset of results, will instead provide a break down of everything it has done, including how it made the table joins and what order it did everything in.

EXPLAIN SELECT a INNER JOIN b ON a.col1 = b.col2 WHERE a.col1 > 1 AND b.col2 > 2;

Speeding up inserts with INSERT DELAYED

Chris — Thu, 12 Jan 2012 11:00:14 +0000

If your insert statements are not time critical, you can use insert delayed in your SQL to speed things up. The syntax is as follows.

INSERT DELAYED table (col1, col2) VALUES ('a', 'b');

Insert delayed can be used with MyISAM and Memory, but cannot be used with InnoDB.

The advantage of using insert delayed is that the MySQL server returns a success message straight away so the script can keep going, without it actually having to do the insert. This allows the MySQL server to carry it out when it isn’t busy, and do several at the same time.

It’s appropriate for tables such as logs tables where it doesn’t matter too much if they don’t go in straight away.

Updating views in MySQL

Chris — Thu, 05 Jan 2012 10:59:16 +0000

Yes, you can update views in MySQL! A lot of people seem to be under the impression that you are unable to, but this simply isn’t the case. There are a lot of restrictive rules, which can be found in the MySQL manual, but as a rule of thumb, you can update them, but only one table.

For example, lets say you have a view which links table A and table B.

You can run an update on this view, but only if you are only updating the columns from one table. So you could run a query that updates a number of columns from table A, or you could run a query which updates columns from table B – but you can’t run a query which updated columns in both table A and table B.

If you need to accomplish this, you need to use a join instead.

Shortcut key for Snapz Pro on Mac

Chris — Sat, 31 Dec 2011 10:57:59 +0000

Snapz really annoys me because I paid money for what is supposed to be the best product out there, but it’s actually incredibly hard to use because every time I want to take a screen shot I have to google for the shortcut key. By default, it’s this.

Cmd + Shift + 3