InstallSnapshot Support snapshot to have directory hierarchy

[宋子阳 <sz...@163.com>]

Hi all,

When follower InstallSnapshot from leader, Ratis will place all snapshot files in a tmp dir, and then rename it to /sm dir. If StateMachine snapshot contains a hierarchy of nested folders, this implementation will flatten the snapshot directory, which causes the hierarchy information to be lost. 

How should StateMachine implement takeSnapshot so that file directory information is maintained during InstallSnapshot? Is is possible for Ratis to support snapshot to have a directory hierarchy?

Best wishes,
William Song

Re: InstallSnapshot Support snapshot to have directory hierarchy

[Tsz Wo Sze <sz...@gmail.com>]

Hi William,

That's a good idea!  There is a TODO in SnapshotManager [1].  It seems that
we may simply create the tmpSnapshotFile with the fileName as below.  Not
sure if it requires other changes.

       // TODO: assumes flat layout inside SM dir

-      File tmpSnapshotFile = new File(tmpDir,

-          new File(dir.getRoot(), fileName).getName());

+      final File tmpSnapshotFile = new File(tmpDir, fileName);


Regards,
Tsz-Wo


[1]
https://github.com/apache/ratis/blob/afd33f77c5e080022ff86725f66c66ae4d9e8d06/ratis-server/src/main/java/org/apache/ratis/server/storage/SnapshotManager.java#L86


On Mon, May 30, 2022 at 1:56 AM 宋子阳 <sz...@163.com> wrote:

> Hi all,
>
> When follower InstallSnapshot from leader, Ratis will place all snapshot
> files in a tmp dir, and then rename it to /sm dir. If StateMachine snapshot
> contains a hierarchy of nested folders, this implementation will flatten
> the snapshot directory, which causes the hierarchy information to be lost.
>
> How should StateMachine implement takeSnapshot so that file directory
> information is maintained during InstallSnapshot? Is is possible for Ratis
> to support snapshot to have a directory hierarchy?
>
> Best wishes,
> William Song
>