[Gluster-users] How to sync content to a file through standard Java APIs

[Sven Ludwig]

Hello,

we have a Gluster FS mounted at some /mnt/... path on a Server. The actual physical device behind this resides on some other Server.

Now, the requirement is to write files to this Gluster FS Volume in a durable fashion, i.e. for an officially succeeded write the contents MUST have been actually synced to disk on at least one of the Gluster FS nodes in the replica set.

Our questions:

1. Which JDK 8 APIs can we use that would fulfill this requirement with an actually working sync?

2. Is java.nio.channels.FileChannel.open with StandardOpenOption#SYNC in the set of options given to this method an option, or would it perhaps not actually guarantee the sync?

3. Apart from 2., are there other ways to achieve the requirement through the standard JDK 8 APIs?

Kind Regards
Sven

[Niels de Vos]

Post by Sven Ludwig
Hello,
we have a Gluster FS mounted at some /mnt/... path on a Server. The
actual physical device behind this resides on some other Server.
Now, the requirement is to write files to this Gluster FS Volume in a
durable fashion, i.e. for an officially succeeded write the contents
MUST have been actually synced to disk on at least one of the Gluster
FS nodes in the replica set.
1. Which JDK 8 APIs can we use that would fulfill this requirement
with an actually working sync?
2. Is java.nio.channels.FileChannel.open with StandardOpenOption#SYNC
in the set of options given to this method an option, or would it
perhaps not actually guarantee the sync?
3. Apart from 2., are there other ways to achieve the requirement
through the standard JDK 8 APIs?

There is nothing special to take care of, all languages should support
the required features. These are the two things you need to take into
account (just like with other filesystems):

1. call a flush() or sync() function after writing to a file(descriptor)
2. when creating a new file (or any directory entry), call flush() or
sync() on the directory where the new entry is created to persist the
metadata of the directory.

See 'man 2 fsync' for a little more details.

HTH,
Niels