Il mar 30 lug 2019, 04:17 Wei Liu <[email protected]> ha scritto: > Thank you very much for your explanation. > > I think the current design is therefore a single writer, who writes the > same message to multiple bookies in parallel(no leader) and the server > updates lac only rely on client submit. > It may result in delay in receiving the last message or in user usage > complexity. >
If you have a continuous stream of data from the writer you get a great throughput and all of the guarantees of BK. If you have very few writes you have to do what I said before . If you are experiencing low throughput consider using the asynchronous API and tune you journal settings on the bookie Enrico > Enrico Olivelli <[email protected]> 于2019年7月29日周一 下午7:07写道： > >> Hello Wei Liu, >> This is about the core feature of BookKeeper, that is the Last >> AddConfirmed Protocol (LAC for friends). >> >> BookKeeper guarantees to the readers that once you read an entry you will >> always be able to read it. >> The reader is able to "see" the entries only after it has the guarantee >> that the writer has received the acknowledgement of a successful write with >> an quorum of bookies. >> >> In order to make it possible the writer "piggy backs" the id of the >> LastAddConfirmed entry to the bookies and the reader then is able to use >> this value (by reading it with readLastAddConfirmed) in order to have this >> reference id. >> >> You have these ways to get your work done: >> 1) write no-operation entries to the ledger, this will make the LAC >> advance even in absence of "application" entries >> 2) use the "ExplicitLAC" feature, that is a background activity that >> sends the current LastAddConfirmed to the bookies even in absence of writes >> after a configurable delay (this is like option 1 but is it automatic, but >> it is still not available in the new API) >> 3) use readUnconfirmedEntries: this bypasses the LAC protocol at all, so >> you can read every entry, but you will need to use an out-of-band channel >> to pass the id of the entries to read >> >> I hope that helps >> >> Enrico >> >> >> >> >> >> >> >> Il giorno lun 29 lug 2019 alle ore 12:49 Wei Liu <[email protected]> ha >> scritto: >> >>> >>> Dear All : >>> >>> 1) First create ledger, add msg 1, 2, 3 into the ledger >>> 2) Do not close the current ledger; >>> 3) Received the msg 1 and 2; >>> 4) Received the msg 3 after closed the ledger; >>> >>> I want to know how to read the last message without close the >>> current ledger? >>> >>> Thanks~ >>> -- >>> 一个人只拥有今生今世是不够的， >>> 他还应该拥有诗意的世界。 >>> >>> [email protected] >>> >> > > -- > 一个人只拥有今生今世是不够的， > 他还应该拥有诗意的世界。 > > [email protected] >
