RockDB data portability (aka empty db issue)

[davidecaroselli]

Hi team!

I'm experiencing some issues with RocksDB:

1. I create a very small database on one machine, let's call it VM1.
2. Stop any process that read/write on that db.
3. SCP the entire db folder from one machine to another, VM2.
4. And now it comes the problem: if I dump the db content with my binary, I get content only in VM1, and an "empty DB" on VM2.

More precisely my code does something like:

it = db->NewIterator();
it->SeekToFirst();

while (it->Valid()) {
   ...
}

Now the problem is that the line it->Valid() it's immediately false on VM2.

Do you know any good reason why I should not be able to do such operation?

Thank you!

[davidecaroselli]

ops, almost forgot! This is the DB that is causing the issue: db.tar.gz and the version of rocksdb is 4.13.5

thanks!

[davidecaroselli]

Just found the solution!
The problem was related to snappy library: rocksdb on VM1 was built with snappy, while rocksdb on VM2 not. When I tried to read the sst file with sst_dump on VM2 I get this error:

/.../000007.sst: Corruption: Snappy not supported or corrupted Snappy compressed block contents

May I suggest to throw this error at DB->Open() instead of silently fail?

Thanks!

[yiwu-arbug]

DB->Open() don't actually read the sst file, but it->Status() should reveal the error. Does it work for you?

[davidecaroselli]

yes, the issue arises if I use it->Status(). I was expecting database to be "readable" after db->Open(), my mistake!

Thanks!