Hi Adrian,

Am Samstag, 7. Januar 2012, 01:33:24 schrieb Adrian Hossu:

> Hi all,

>

> I'm been running basex on two environments, one is my laptop with an SSD

> drive and ext4, the other is a server with raid-1 HDD and ext3.

>

> Using iotop, I am watching the disk access of the server and laptop, and

> comparing the two.

>

> After some update queries, I notice that the server (ext3) has a process,

> [kjournald], which writes for about 20 seconds at 600-1000KB/sec.

kjournald is a kernel thread which updates the journal [1] of the file system.

> This only begins after the update is complete and the java process actually

> stops writing. I am not experiencing such a thing on my laptop. If I do

> too many of these queries on the server, it will eventually hang for 20-30

> seconds.

Ext3 (and ext4) have different levels of journaling [2], defining what and when gets written to the journal and the main file system.

It sounds to me, as if your file system is journaling both meta-data and file contents, since kjournald write a lot of data.

I suggest, that you check with what arguments your file systems are mounted. Generally, you can see that in /etc/mtab; the corresponding line should contain something like "data=ordered". You could also check the documentation of your linux distribution.

> I've copied the exact data on both the laptop and the server.

>

> Are there any recommended filesystem types for basex?

Personally, I'm not aware if there is a recommended file system, I think no, but generally it Should Just Work(tm). However, if someone has experimented with different types of file systems and/or types of disks may share results.

> Does it sound like

> I've configured something incorrectly, or should I add some more drives to

> my server and have them using ext4? Or is the difference SSD vs HDD? I

> never saw my SSD write speed go above 200KB/sec or so during the same

> queries.

>

> Any help would be greatly appreciated!

>

> - Adrian

Regards,

Dimitar

P.S. it's recommended to use Btrfs with SSDs, since the file system is designed to improve the wear leveling of the disk [3].

[1] http://en.wikipedia.org/wiki/Journaling_file_system

[2] http://en.wikipedia.org/wiki/Ext3#Journaling_levels

[3] http://en.wikipedia.org/wiki/Btrfs