Hi Joe,
Then what would we expect users to do with the MessageId? It should only
be passed to Consumer#seek or ReaderBuilder#startMessageId?
What about the partition index? We have a `TopicMetadata` interface that returns
the number of partitions. If the partition is also "implementation
details", should we expose
this interface? Or should we support customizing a MessageRouter because it
returns the partition index?
What about the batch index and batch size? For example, we have an
enableBatchIndexAcknowledgment method to enable batch index ACK. If batch
index is also "implementation details", how could users know what does "batch
index ack" mean?
Even for ledger id and entry id, this pair represents a logic storage
position like the offset
concept in Kafka (though each offset represents a message while each
entry represents
a batch). If you see the Message API, it also exposes many attributes.
IMO, for the
MessageIdData, only the ack_set (a long array serialized from the
BitSet) is the implementation
detail.
The MessageId API should be flexible, not an abstract one. If not, why
do we still implement
the toString() method? We should not encourage users to print the
MessageId. It would
be easy to know what "ledger is 0, entry id is 1" means, users only
need to know the concepts
of ledger id and entry id. But it would be harder to know a tuple like
"0:1:-1:-1" means.
Thanks,
Yunze
On Tue, Nov 8, 2022 at 11:16 PM Joe F <joefranc...@gmail.com> wrote:
>
> >Maybe this design is to hidden some details, but if
> users don't know the details like ledger id and entry id, how could
> you know what does "0:0:-1:0" mean?
>
> Abstractions exist for a reason. Ledgerid and entryid are implementation
> details, and an application should not be interpreting that at all.
> -j
>
>
> On Tue, Nov 8, 2022 at 3:43 AM Yunze Xu <y...@streamnative.io.invalid>
> wrote:
>
> > I didn't look into these two methods at the moment. But I think it's
> > possible to
> > retain only the `fromByteArray`.
> >
> > Thanks,
> > Yunze
> >
> > On Tue, Nov 8, 2022 at 7:02 PM Enrico Olivelli <eolive...@gmail.com>
> > wrote:
> > >
> > > Il giorno mar 8 nov 2022 alle ore 11:52 Yunze Xu
> > > <y...@streamnative.io.invalid> ha scritto:
> > > >
> > > > Hi Enrico,
> > > >
> > > > > We also need a way to represent this as a String or a byte[]
> > > >
> > > > We already have the `toByteArray` method, right?
> > >
> > > Yes, correct. So we are fine. I forgot about it and I answered too
> > quickly.
> > >
> > > I am not sure if this can be in the scope of this initiative, but we
> > > should somehow get rid of
> > > stuff like "fromByteArrayWithTopic" vs "fromByteArray".
> > >
> > > Thanks
> > > Enrico
> > >
> > > >
> > > > Thanks,
> > > > Yunze
> > > >
> > > > On Tue, Nov 8, 2022 at 6:43 PM Enrico Olivelli <eolive...@gmail.com>
> > wrote:
> > > > >
> > > > > Il giorno mar 8 nov 2022 alle ore 11:25 Yunze Xu
> > > > > <y...@streamnative.io.invalid> ha scritto:
> > > > > >
> > > > > > Hi all,
> > > > > >
> > > > > > Currently we have the following 5 implementations of MessageId:
> > > > > >
> > > > > > - MessageIdImpl: (ledger id, entry id, partition index)
> > > > > > - BatchMessageIdImpl: adds (batch index, batch size, acker),
> > where
> > > > > > acker is a wrapper of a BitSet.
> > > > > > - ChunkMessageIdImpl: adds another MessageIdImpl that represents
> > > > > > the first MessageIdImpl of a BitSet.
> > > > > > - MultiMessageIdImpl: adds a map that maps the topic name to the
> > > > > > MessageId.
> > > > > > - TopicMessageIdImpl: adds the topic name and the partition name
> > > > > >
> > > > > > These implementations are such a mess. For example, when users get
> > a
> > > > > > MessageId from `Producer#send`:
> > > > > >
> > > > > > ```java
> > > > > > var id = producer.send("msg");
> > > > > > ```
> > > > > >
> > > > > > There is no getter to get some specific fields like ledger id. You
> > can
> > > > > > only see a representation from `toString` method and got some
> > output
> > > > > > like "0:0:-1:0". Maybe this design is to hidden some details, but
> > if
> > > > > > users don't know the details like ledger id and entry id, how could
> > > > > > you know what does "0:0:-1:0" mean? What if `MessageId#toString`'s
> > > > > > implementation changed? Should it be treated as a breaking change?
> > > > > >
> > > > > > The original definition of the underlying MessageIdData is much
> > more
> > > > > > clear:
> > > > > >
> > > > > > ```proto
> > > > > > message MessageIdData {
> > > > > > required uint64 ledgerId = 1;
> > > > > > required uint64 entryId = 2;
> > > > > > optional int32 partition = 3 [default = -1];
> > > > > > optional int32 batch_index = 4 [default = -1];
> > > > > > repeated int64 ack_set = 5;
> > > > > > optional int32 batch_size = 6;
> > > > > >
> > > > > > // For the chunk message id, we need to specify the first
> > chunk message id.
> > > > > > optional MessageIdData first_chunk_message_id = 7;
> > > > > > }
> > > > > > ```
> > > > > >
> > > > > > IMO, MessageId should be a wrapper of MessageIdData. It's more
> > natural
> > > > > > to have an interface like:
> > > > > >
> > > > > > ```java
> > > > > > interface MessageId {
> > > > > > long ledgerId();
> > > > > > long entryId();
> > > > > > Optional<Integer> partition();
> > > > > > Optional<Integer> batchIndex();
> > > > > > // ...
> > > > > > ```
> > > > >
> > > > > This is very good for client applications.
> > > > > We also need a way to represent this as a String or a byte[], this
> > way
> > > > > client applications have a standard way to store
> > > > > message offsets into an external system (for instance when you want
> > to
> > > > > user the Reader API and keep track of the position by yourself)
> > > > >
> > > > > Enrico
> > > > >
> > > > > >
> > > > > > Additionally, there are many places that use only the triple of
> > > > > > (ledger id, entry id, batch index) as the key to represent the
> > position.
> > > > > > Currently, they are done by adding a conversion from
> > > > > > BatchMessageIdImpl to MessageIdImpl. However, it's more intuitive
> > to
> > > > > > write something like:
> > > > > >
> > > > > > ```java
> > > > > > class MessageIdPosition implements Comparable<MessageIdPosition> {
> > > > > > private final MessageId messageId;
> > > > > > // TODO: compare only the triple (ledger, entry, batch)
> > > > > > ```
> > > > > >
> > > > > > Therefore, I'm going to write a proposal to redesign the MessageId
> > > > > > interface only by adding some getters. Regarding the 5 existing
> > > > > > implementations, I think we can drop them because they are a part
> > > > > > of `pulsar-client`, not `pulsar-client-api`.
> > > > > >
> > > > > > Please feel free to share your points.
> > > > > >
> > > > > > Thanks,
> > > > > > Yunze
> >
