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.
Enrico Olivelli <eolive...@gmail.com> 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 <liuwe...@gmail.com> 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。
>>
>> liuwe...@gmail.com
>>
>
--
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。
liuwe...@gmail.com
