So I understand the rationale for writing your own storage layer and think this is an awesome project, but there's something missing for me. One of the issues Peter brings up is they've come across a number of serious bugs in RocksDB. My question is, why would Pebble have less bugs. In fact, I would expect it to have significantly more bugs because Coackroach is the only company using Pebble.
They mention briefly how they are going about randomized crash testing:
> The random series of operations also includes a “restart” operation. When a “restart” operation is encountered, any data that has been written to the OS but not “synced” is discarded. Achieving this discard behavior was relatively straightforward because all filesystem operations in Pebble are performed through a filesystem interface. We merely had to add a new implementation of this interface which buffered unsynced data and discarded this buffered data when a “restart” occurred.
but this seems to only scratch the surface of possibilities that can come up with a crash. For example, it's possible the filesystem had synced some of the buffered data to disk, but not all of it. There's no guarantee about what buffered data was synced to disk. All you know is that some, all, or none of it made it to disk.
Bugs in this area are still regularly found in e.g. Postgres, so I'm having a hard time seeing how Coackroach is making sure Pebble doesn't have similar problems.
They mention briefly how they are going about randomized crash testing:
> The random series of operations also includes a “restart” operation. When a “restart” operation is encountered, any data that has been written to the OS but not “synced” is discarded. Achieving this discard behavior was relatively straightforward because all filesystem operations in Pebble are performed through a filesystem interface. We merely had to add a new implementation of this interface which buffered unsynced data and discarded this buffered data when a “restart” occurred.
but this seems to only scratch the surface of possibilities that can come up with a crash. For example, it's possible the filesystem had synced some of the buffered data to disk, but not all of it. There's no guarantee about what buffered data was synced to disk. All you know is that some, all, or none of it made it to disk.
Bugs in this area are still regularly found in e.g. Postgres, so I'm having a hard time seeing how Coackroach is making sure Pebble doesn't have similar problems.