Log based recovery – To ensure consistency after a crash or interruption of a transaction (bunch of queries), log files are used to check what made it from the cachemanager to the physical disk before the interruption. All committed translations (in the log but not database/disk) are normally redone, while transactions with only a start marker is reverted/undo. This is the basis for 4 concepts of log based recovery; undo/redo, no-undo/redo, undo/no-redo, and no-undo/no-redo.

Two-Phase Locking – For consistency during a transaction the order of which reads and writes are made to a row/table/database is essential. Locking makes it possible to restrict access to (lock) a row/table/database and have exclusive right to (exclusive lock) write a value, excluding everyone else until the restricting is lifted (unlock). Likewise when a exclusive lock is active, no-one can read the row/table/database. Lastly, if only a read is made a simple shared lock is used, other transactions can also read the same row/table/database at the same time, placing more shared locks. Once a transaction wants to write, an exclusive lock is requested.

For structure and order all transactions need to lock in the beginning and unlock before finishing, this creates a phase system. Phavse 1 is the start and phase 2 finishing the transation. A transaction changes phase once a lock is released or lock is downgraded from exclusive to shared. In phase 2 new locks can not be requested and shared locks can not be upgraded, thus the transaction is in the unlock/falling phase. The opposite is phase 1 where locks can be made and shared can be upgraded to exclusive.

The illustrations:

• DAT202: Recovery – Undo/Redo
• DAT202: Concurrency – Two-Phase Locking

• Matrix calculations on Casio
• Matrix calculations on TI

The guides are in Norwegian and I actually got it published for the MA-109 course at UiA. They might be useful for others too.

To use the sound as a text message-tone on an iPhone, you need a jailbroken device and a AIFF version of the file. Download the already converted and corretly named file:

• sms-received6.caf
• droid-alert.wav

Or convert it yourself. In iTunes change the Import settings in Preferences to AIFF, add the droid sound to the iTunes library and right-click it, pick Convert to AIFF, drag the new AIFF file to the desktop, rename it to sms-received6.caf.

Connect to the iPhone via SCP and go to /System/Library/Audio/UISounds/. Rename the existing sms-received6.caf to sms-received6-org.caf, and upload the new droid sms-received6.caf. Go into Settings, Sounds, New Text Message, and pick Electronic as the SMS sound. Voila!

To use it as a ringtone, just sync this droid-alert.m4r with the iPhone in iTunes.

The alternatives are XFS, ReiserFS, JFS, Ext3, and Ext4. Ext3 is excellent is an excellent system boot FS and for lots of smal files, but not as efficient for larger files.

Drive: Hitachi 7K1000.B 1TB via Promise SATA300 TX2plus PCI card (I know)
Software: Bonnie++ 1.03d harddrive benchmark, executed by bonnie++ -u 500:500

hdparm – for reference, shows the cache and disk read speeds
Test done using: hdparm -tT /dev/sda

• Timing cached reads: 976 MB in 2.00 seconds = 487.76 MB/sec
• Timing buffered disk reads: 294 MB in 3.02 seconds = 97.39 MB/sec

The test will first create then rewrite a 1GB file.

Ext3
Formatted using: mkfs.ext3 -j -c 1 /dev/sda1

• Block write: 74 781 KB/s
• Rewrite: 38 624 KB/s
• IOPS: 209.7

XFS
Formatted using: mkfs.xfs -f /dev/sda1

• Block write: 91 373 KB/s
• Rewrite: 45 176 KB/s
• IOPS: 212.2

XFS tuned
Formatted using: mkfs.xfs -f -l size=128m,lazy-count=1 /dev/sda1

• Block write: 91 828 KB/s
• Rewrite: 44 565 KB/s
• IOPS: 215.9

ReiserFS3
Formatted using: mkfs.reiserfs /dev/sda1

• Block write: 83 391 KB/s
• Rewrite: 43 003 KB/s
• IOPS: 225.0

JFS
Formatted using: mkfs.jfs /dev/sda1

• Block write: 81 466 KB/s
• Rewrite: 43 330 KB/s
• IOPS: 234.0

The benchmarks look good, but they only tell a small part of the puzzle. It’s important to not to forget the stability and reliability record for each FS. How it will behave in a power failure and unexpected situations? From experience will ext3/4 perform great in these scenarios, XFS, ReiseFS, and JFS not so much according to forum reports.

More testing and experience is needed to figure out how these filesystems stack up.

• XFS Filesystem performance tweaking on Linux
• New ext4 vs XFS benchmarks
• Linux benchmarks applications
• Benchmarking Filesystems

Østregate:

Sam Eydes plass:

Certainly makes me at LEAST 3% more productive. Take a look at the screen-capture I made below.

A class can have a collection of functions that belong to a specific part, or say, module of a site. Instead of having functions (function name () {}) listed alone in a file and available in the global scope, i.e include once and the function will be available till the end of the execution. A function inside a class can only be called upon by the name of the object or inherit of itself(this.).

Which brings me to objects, a class is the code that lists the available functions, but a object is a run-time instance of the class and its functions can be addressed via the name of the new instance ($db = new Mysql();). Think of object like e.g. creating a new tab in web-browser.

// Mysql class
class Mysql {
   function connect($host, $name, $pass, $db) {
      $connection = mysql_connect("$host","$name","$pass");
      mysql_select_db("$db", $connection) or die("Couldn't select database.");;
   }

// Send query
$db->query("SET CHARACTER SET 'utf8'");


Pretty cool and handy!

iPhone, yes, I’m pretty sure you have heard the name a couple of times before.

I decided to get the next generation iPhone, the iPhone 3G, on the launch date to get the excitement. Contrary to the first iPhone I got in October 2007 when the jailbreaking and unlocking was properly set up.

Ok, to the main story. In Norway the iPhone 3G is only sold by the Netcom operator via its Telebutikken stores. My goal was to get an iPhone 3G, with a new contract, break the contract, and activate it with my previous SIM-card from Telenor.

At 13.15 I arrived at the store, around 5-8 waiting in queue before me. The buying process was interesting, there was no properly set up queuing system in the store. I had to find my own piece of paper and write the next incremental in the queue. I got 82 and number 73-75 was processing then I got there. A little over an hour later, I’m ready to go.

The buying process is a two parter:

• Pick your iPhone, in my case 16GB black for 2290 NOK, credit check and pick existing or new contract, I choose new of course.
• Go over to the activation desk, asked if I could activate with my other SIM-card, but he had strict guidelines to only activate new devices with Netcom SIM-cards, gave me the 05050 customer service number for more details, very nice guy, shaked the hand of every iPhone customer.

At this point, I have an activated iPhone 3G with a new Netcom iTalk small contract. This is where most people would end up and start using the iPhone, but I want to use my current SIM-card.

I called the customer service and they actually had three menu choices, the third being “Press 3 for iPhone”. A friendly women quickly picked up (I guess they have extra staff) and I explained I wanted to go out of the new contract and use my current operator. To cancel the iTalk small contract would cost 2400 NOK plus the first month of the contract, 399 NOK. An invoice will be sent to my address.

This cancel process is also a two parter:

• She asked for the phone number to find the contract, asked if I was sure I wanted to terminate the contract, yes please.
• Next, asked for the unique IMEI (International Mobile Equipment Identity) number, printed on the same piece of paper with the contract phone number, used it to deactivate the phone in the Netcom network, sent a request to Apple to indicate the device should be unlocked, this happens next time I connected it to iTunes (at home) she told.

I played with the iPhone during the trip home and I noticed the Maps locate-me functions didn’t find my position. I hope this was because I didn’t have a cell signal, although it wouldn’t make sense. Even with a Wifi connection to allow any A-GPS data cache to be downloaded didn’t work.

The screen has a noticable yellow hue compared to the same brightness level. Not as crystal crisp white as the original (quality control?). It seems the white balance is a tad warmer. Apple confirmed that the white balance is warmer on the iPhone 3G, around 7000K compared to 8000K in the 1. gen.

To make it pick up the new SIM-card I had to do a full restore, and to complete the set up it was to connect to the iTunes (activation) servers. This was 17.00 CET/Norwegian time while the rest of the US was about or in the middle of waking up to iPhone launch day, making the iTunes servers crawl to a total halt. Finally at 21.15, the activation was successful, iTunes only needed a quick query to Apple to determine the lock state, fortunately it unlocked without needing any interaction. The next screen was the select previous backup or create new device profile set up.

There is also a store activation mode in iTunes, it looks like just a more automated hook-up-activate-disconnect procedure.

Mac: /Applications/iTunes.app/Contents/MacOS/iTunes -StoreActivationMode 1
Windows: “C:\Program Files\iTunes\iTunes.exe” /StoreActivationMode 1

• The total cost: 2290 + 2400 + 399 = 5089 NOK

That places it in the higher end of the smartphones sold in Norway, e.g. the Nokie N95 8GB is sold without contract for 4850 NOK.

My plan is to buy another iPhone 3G 16GB unlocked in US (via a friend, Ebay, some other place) for cost (around 700 USD) once the launch day excitement plays out, import it to Norway, jailbreak it to add Installer.app (Dev Team is ready), and sell it to little under the unlocked cost in Norway to cover some of my expenses (around 1500 NOK).

With a new design also comes less compatibility, the old iPhone dock no long fits the new iPhone 3G. Not a big issue. The corner shape is pointier and not as round as before. My iPod 3G 2003 dock still fits and works perfectly though.

Edit: Only major advantages with an iPhone 3G over the 1. generation for me is: 1. GPS, 2. 16GB, the rest is irrelevant, and the 2.0 software is the same on both. Sold for 9000 NOK. Apparently, VG mentioned to watch out for iPhone price “coups” (the one mentioned is not mine, but there were only two auctions, the other being mine).

As a reference for myself I’ve created a quick entry to show how to use a regular downloadable floppy image and an image utility to create a bootable disc including all the files you want to execute once DOS has been loaded.

• Create bootable disc

Now, today after updating my e-mail server to better fight spam and bounce spam, I decided to do a clean-up of the blog comments. A quick search for ‘wordpress captcha plugin’ reveal a type of captcha I remeber liking because it wasn’t that unfriendly and time consuming to figure out. It’s called Recaptcha. It requires a API key since it’s essentially streaming the code in the background to the Recaptcha servers.

Preview:

Hopefully this isn’t to intrusive and bothersome. It cuts out all the un-necessary spam I was receiving and I’m happy about that.

Update: Recently I discovered that Recaptcha actually helps the Internet Archive project and digitize books, thus helps the optical character recogonition (OCR) system.