Today I was asked about this bit of code that appears in some of the examples MySQL has for engine designers:

memcpy(record, ptr, table->s->null_bytes);

What is exactly going on here?

Whenever we read a row, or write a row the method looks something like this:

int ha_example::write_row(byte *record)

"record" is a byte array of data that makes up the row. The first bytes of it store whether fields are null or not. Values for columns are then stored in order after the null bytes. Most engines never look at "record" directly, and instead use Field objects to look at, or set the current record. To do this you typically setup a for loop like so:

for (Field **field=table->field ; *field ; field++)

Field has both store and value functions that allow you to manipulate the data. When storing a field you typically call:
…

Just for reference, here are some previous posts I did for the 2005 MySQL User Conference:

• Day 0
• Day 1
• Day 2
• Day 3
• Day 4

Not that these are particularly awesome or anything, but there are a few travels notes which may possibly be useful if you decide to go this year, since it's in the same location.

If you have the time, and you are from outside The Valley, catch …

On Server and Storage Engines

Q from Alessandro: What about the filesystem for MyISAM in a small company? Better ReiserFS or EXT3?
As Anders said, it's a matter of taste. XFS is a good alternative too. Ext3 is stable, but sometimes slow and a bit outdated. Many like Reiser, but it is sometimes difficult to manage. XFS often gives you good performance and reliability out of the box.

Q from Florian: MySQL 5.1 == Falcon?
Falcon is available for download today. The current version refers to 5.2 and it's an alpha version. We may change plans, but so far Falcon is related to version 5.2

Q from Henk: Will InnoDB ultimately be replaced by Falcon?
No, it will not. Falcon is an alternative to InnoDB and willl be especially excellent for online applications, but we will continue to support InnoDB for many …

Today, FSF released the third GPLv3 draft on http://gplv3.fsf.org/gpl3-dd3-guide . It’s great that the entire, complex process now has completed its next milestone, and I can fully understand why the FSF has seen it necessary to proceed at a pace somewhat slower than originally intended.

My thoughts go back well over a year to the Free Software Foundation’s first conference on GPLv3, at the end of January 2006. It was a great meeting, and as a Committee B member and representative of MySQL, I was asked by China Martens of IDG for my input. My reply “I think there was a good balance between different hair and beard lengths” ended up on China’s compilation “2006: The IT …

Last august, I started wanting a new API for MySQL Cluster that could solve a few problems. Frist, if you were to use MySQL Cluster in a LAMP application, you would be turning a two-layer architecture (Apache and MySQL) into three layers (Apache, MySQL, and NDB). Adding that extra tier requires more hardware and means slower response times. Second, the one way around this was to write native NDB API code in C++, but learning the API and developing low-level code can require a big commitment of time. I wanted an easier way to eliminate the extra layer.

My solution is called mod_ndb, and it is an Apache module that runs inside a web server and connects directly to the MySQL Cluster data nodes. It supports a "RESTful" API -- applications make GET, POST, and DELETE requests over HTTP, and mod_ndb provides appropriate HTTP responses. Because it is HTTP, responses can be cached by proxies in a well-defined way, and data can be delivered …

Evans Data Group has recently released the results of their latest developer survey showing that MySQL usage is up by 25%.  In fact, 40% of developers surveyed are using MySQL.  According to Evans:

"In an increasing number of ratings categories, we're seeing open-source databases meeting or exceeding proprietary databases."

Evans indicated that MySQL was growing in popularity due to its adoption as part of the open source LAMP stack (Linux / Apache / MySQL / PHP).  With more developers using open source (65% in North America) MySQL usage is expected to continue to grow in the future.

• Evans Data: MySQL Gains 25% Market Share of Database Usage
• CNet: …

I blogged some months ago about an article written by Mr Puhakka on how to build a billion dollar business around open source software. Last Friday I attended Mr Puhakka’s presentation where he analyzed MySQL’s possibilities on becoming so (copied from his slides):

1. Find or create a great value proposition. The price vs. quality ratio of MySQL is in place or even superior as MySQL has this with its database offering costing a fraction of competing incumbents.
2. Find a quickly growing market. Rapidly growing markets tend to be much more forgiving of mistakes than …

This is a good read for anyone who has ever tried to pivot data from a table in MySQL using client side code like PHP when you can with some careful query construction do it in MySQL.
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Copyright 2006-2008 Andrew Rose [rose.andrew@gmail.com] [andrewrose.co.uk]

I’ve used OfflineIMAP for quite a while now. On the whole I’m fairly happy with it. Today I sent this to the list:

Forgive the potentially bad python, not my native tongue :)

This patch is motivated by three things:
- offlineimap is extremely slow at syncing lots of locally deleted
messages
- offlineimap uses lots of memory
- LocalStatus files aren’t written safely (a hard crash can cause
corruption)
        - I’ve been bitten by this in the past, causing a complete resync of
the folder… so I get duplicate messages.

I am currently using 4.0.14 (from Debian) with this patch. I used it to
convert the files and everything. Seems quite reliable and quick.

In my tests, execution time for a normal sync is relatively the same.

Execution …

Having taken a look at the 35 MySQL Summer of Code applications, I can now say that we have several very strong applications, such as:

• IPv6: Enabling MySQL to connect over IPv6 internet
• MySQL Based Atom Store (storing Google GDATA in MySQL)
• Test case development / Load testing
• Test suite development
• MySQL Auditing Software
• The “anti-profiler” - a performance analysis tool for database engines

For several of the above, we have multiple good applications. The applicants come from recognised universities across the world, not just the US and Europe. Some have extensive experience from professional software development. Sadly, we will end up having to reject several …