Some applications require direct access to a block device, without an intermediate file system. Some Oracle and MySQL configurations are an example, as are some Xen setups, or IET. Can you do this with DRBD? Sure you can.

However, you need to fulfill two prerequisites:

1. Your application can’t access DRBD while it’s in the Secondary role. So, you must make sure DRBD is Primary before your application attempts using that device.
2. The user in whose context your application runs needs read/write access to that device.

Your cluster manager, when configured properly, normally takes care of item #1 for you. #2 is a little trickier:
Normally, DRBD’s device nodes are owned by root:disk, with permission bits set to 0660 (rw-rw----). So in order to allow your application to use the device, you have two options:

• Add …

A question I recently got from our friends at MySQL:

When speaking about DRBD, we mention that if you upgrade your Linux kernel, it is important that you also upgrade the version of DRBD appropriately.
Question: When upgrading the kernel via yum/yast, does it automatically detect that you should also upgrade your DRBD module?

The answer is, as always, a clear and resounding “it depends.”
Let’s break this down by distribution.

• If you’re on Debian and updating your linux-image package, dpkg will complain about an unresolved dependency from the DRBD kernel module package, forcing you to update that as well.
• If you’re on Debian and adding a more recent linux-image package, it’s up to you to remember to install a new DRBD kernel module package as well.
• If you’re on …

A few days ago, Alexander Barkov pushed some changes to the MySQL 5.1 tree that I’ve been waiting to see for some time — variable support for XPath functions used with ExtractValue() and UpdateXML(). (This was a fix for Bug #26518, BTW.) This will be available in MySQL 5.1.20 (or grab the MySQL 5.1 source from bkbits and build it yourself, if you just can’t wait).

Two slightly different notations are supported, depending on the context, and what sort of checking you want done on the values:

1. If you don’t want or need type checking, prefix the variable name with $@, like this: $@myvar. However, if you do this, and you make a typo, you’re on …

Linus is right when he talks about the performance of SCMs…. and that BitKeeper was about the first one to be worth using at all (really).

But as an interesting speed comparison… I’ve managed to pull the latest git (with git) and build it in less time than BitKeeper has taken to pull the latest NDB tree…. hrrm..

One of the reasons I’m so enjoying quilt for every day hacking is that it is blindingly fast.

Since starting the innotop and mysqltoolkit projects on Sourceforge, I have learned a lot about how to use source control more effectively -- especially how branching and tagging can be used. Still, I have limited experience. I want to package all the tools in MySQL Toolkit together and release them in one archive, but I don't know the best way to do it; every idea seems to have drawbacks. Read on for the details, and if you have suggestions, would you please leave comments for me?

MySQL Table Checksum 1.1.6 enhances chunking, adds features and fixes bugs. The chunking functionality is where I continue to put most of my effort. This release's behavior is incompatible with the last release, and it will probably change again in the future.

Thanks to everyone who has been helping me chase down bugs, including one user who sent me a major patch! It's a great feeling to get a patch.

Dathan says that 128k Stripe Size is ideal for INNODB:

128K - this is really good for INNODB, you’ll see a huge boost in responsiveness by making your Stripe Size 128K. I had a 64K stripe size, and I was blown away by the improvement of 128K

I’ve only benchmarked 64k and 1M. Google is using a 1M stripe size. 1M was about 5x slower for our workload. I’m going to have to benchmark 128k.

Interesting that he recommends RAID 10. We’re using RAID 0 and just using a Redundant Array of Inexpensive Servers. If one fails we just promote another one as master.

Announced at the 2007 Conference as MySQL Applications of the Year - #1 in 3G Mobile Entertainment, Amp’d Mobile is no longer the poster boy.

Amp?d Mobile Implodes: Burns $360 million, Declares Bankruptcy. Wow, that’s news on a Sunday.

I have some warm up questions on how MySQL handles LOBs internally and then some questions on high availability. Especially with HA I feel like I have heard all/most the solutions, but they all seem to lack in one area that really makes you hurt, but I keep stumbling over questions from people asking me which way to go. Finally I have a little backup question for extra credit at the end.

So for the LOB questions, I am wondering if MySQL (or any of the storage engines) store the actual LOB data on separate data pages or not. I am also wondering if the MySQL query cache has any special handling for LOBs, like ignoring all queries that fetch LOB data. I guess there is a setting to set the maximum size for a result set to go into the query cache that could be employed to prevent a few large LOBs to fill up the query cache, but then again you …

The part of software building I called essence is the mental crafting of the conceptual construct; the part I called accident is its implementation process --Frederick Brooks1

Data warehousing involves considerable amounts of accidental and essential complexity. While being a satisfying pursuit when successful, data warehousing is also decidedly prone to failure. You need to learn to manage the essential complexity and eliminate the accidental.

Data warehousing deals with accidental complexity resulting from availability of …