JV, 1) for the real world use case, this is the problem I have hit which I have to manually add a flag in the ledger metadata to avoid serializing ctime. https://github.com/apache/bookkeeper/blob/master/bookkeeper-server/src/main/java/org/apache/bookkeeper/client/LedgerMetadata.java#L105
2) > We have introduced customMetadata in the past and that was not mandatory. How did we make that work with text format? by default if you don't use customMetadata, customMetadata is not serialized into metadata. so there is no problem for rolling back if you don't use this feature. so that's why it wasn't a problem for most of the people. the ctime field was the problem. 3) > At this point, I am not sure if we have identified all the pieces and if they fit together. > Enrico, are you driving the roll-back story? or whoever, can you please come up with a comprehensive proposal? we have a good-enough story for upgrading/rolling-back on wire-protocol and disk formats. however we don't have a good story on metadata part. that's why I sort of pulling in the metadata piece only. however if filling in a big picture would help discussing this problem, I can drive the whole picture for this roll-back story. - Sijie On Mon, Jul 30, 2018 at 7:55 AM Venkateswara Rao Jujjuri <jujj...@gmail.com> wrote: > We have introduced customMetadata in the past and that was not mandatory. > How did we make that work with text format? > > Also, my preference is to wait until we have a need to introduce a new > field for this conversion if needed. > > JV > > On Mon, Jul 30, 2018 at 12:42 AM, Enrico Olivelli <eolive...@gmail.com> > wrote: > > > Il giorno lun 30 lug 2018 alle ore 09:17 Ivan Kelly <iv...@apache.org> > ha > > scritto: > > > > > >> Thank you for putting this together. It is also good to put this as > a > > > BP, > > > >> since it is about the metadata layout. > > > > > > I'll put a BP up this week once I have initial feedback. > > > > > > >> > - When writing a metadata, check what is in /ledgers/LAYOUT. If it > > is > > > >> > as above, write using the current text protobuf. If is bumped, use > > the > > > >> > new binary format. > > > > > > > > isn't it too costly? Adding a zk read for each write. We could add a > > > watch > > > > but is has an important cost > > > > > > This cost can be amortized. In simplest case, we only read when client > > > starts (as already happens). Client are able both read and write the > > > old format, so clients that read the pre-upgrade version will still > > > write in text format, and this is fine. > > > > > > > For me it is fine to read it when client starts. A rolling restart of the > > client application will be enough to load the new configuration. > > > > > > > > > > However, we would want them to eventually see the new format without a > > > restart. At one extreme, we could put a watch on the znode, but this > > > could be quite heavy (I think the only per-client watch we have now is > > > on /ledgers/available). Alternatively, we could just read > > > /ledgers/LAYOUT once per day. This way clients who saw the old version > > > will eventually get updated. > > > > > > > I prefer NOT to use the watch, this cost will be payed forever even when > > there will be no configuration changes. > > > > I would go with the 'load at start' option, it is clear and works fine > > > > > > > > > > > > > What about having a client side config writeMetadataVersion ? > > > > We start a new metadata version, the new one will be encoded as > > binary. > > > > By default 4.8 clients will use previous version, as we already do > for > > > > journal and fileinfo on bookies. > > > > > > > > Each ledger is independent from the others, there is no need of a > > global > > > > flag written on zk. > > > > > > There is a global property here though,which only the administrator > > > can control. It is "Can all clients in the cluster/application read > > > the new ledger metadata version?". This is why I'd like to keep it as > > > a centralized flag rather than allowing each client to decide for > > > themselves. > > > > > > > ok, let's keep it > > > > Enrico > > > > > > > > > > > > > Don't we already have some tool? (Maybe I only have seen such tool in > > my > > > > company applications) > > > > > > It may already exist, I haven't checked. > > > > > > -Ivan > > > > > > > > > -- > Jvrao > --- > First they ignore you, then they laugh at you, then they fight you, then > you win. - Mahatma Gandhi >
