Re: Changing ledger metadata to binary format

[Ivan Kelly <iv...@apache.org>]

On Thu, May 30, 2019 at 12:15 AM Venkateswara Rao Jujjuri
<ju...@gmail.com> wrote:
>
> > "Let's decide this when we need it"
>
> Right. This is the time as we are trying to add fault domain info to the
> cookie.

When you say cookie, you mean under /ledgers/cookies? That falls
outside the scope of binary metadata.

> > to make a flag in the metadata store that we flip to enable it.
> Right I do recall the same. But given your proposal in this thread, all
> readers try to read in binary format,
> if that fails they fail back to text mode.

Actually, it doesn't even need this fallback, as the version of the
metadata is stored at the very start, so we switch on that.

> If this is the case, does the following make sense?
> 1. Bookies are updated first with new version. Replication workers
> recognize binary/text format and any metadata updates happen in the same
> format.
> 2. Clients are rolled out later with a caveat that the ledgers created by
> new clients can't be read by old clients. This may be ok as long as they
> don't share
>     the same ledgers.
> With these two things, do we need an explicit flip to enable?

This works, but you need to expose a mechanism in the client to tell
it to write in V3.

As long as old clients don't try and read, there should be no problem.

> I can read the patches again, but let me ask :) did we take care of bookie
> shell also to understand binary format?

Yes, bookie shell can understand it since it reads though the same interfaces.

-Ivan