[Gluster-users] Atomic file updates

[Tom Munro Glass]

I'm not currently a Gluster user but I'm hoping it's the answer to a
problem I'm working on.

I manage a private web site that is basically a reporting tool for
equipment located at several hundred sites. Each site regularly uploads
zipped XML files to a cloud based server and this also provides a web
interface to the data using apache/PHP. The problem I need to solve is
that with a single server disk I/O has become a bottleneck.

The plan is to use a load balancer and multiple web servers with a
4-node Gluster volume behind to store the data. Data would be replicated
over 2 nodes.

The uploaded files are stored and then unzipped ready for reading by the
web interface code. Each file is unzipped into a temporary file and then
renamed, e.g.

file1.xml.zip --unzip--> uniquename.tmp --rename--> file1.xml

Use of the rename function makes these updates atomic.

How can I achieve atomic updates in this way using a Gluster volume? My
understanding is that renaming a file on a Gluster volume causes a link
file to be created and that clearly wouldn't be appropriate where there
are frequent updates.

I could use flock, exclusive for writing and shared for reading, but too
many reading processes could potentially block writing.

Any advice will be much appreciated.

Tom