+1 Thanks, Haiting
On 2022/04/06 08:54:05 Zixuan Liu wrote: > Hi Pulsar community, > > Start voting for PIP-150: https://github.com/apache/pulsar/issues/14883 > > Thanks, > Zixuan > > ----- > > Discussion thread: > https://lists.apache.org/thread/n3drk2g2oy766qnbtx17knvtssy3tdyl > > ## Motivation > > Currently, the Pulsar-client supports setting the `startMessageId` for > Consumer and Reader, and also supports reading the message of > `startMessageId` position. > > Assume, we have two message id 1,2,3,4 in the topic: > > - When we set `earliest` as `startMessageId` value, we can get the message > of message id 1 > - When we set `latest` as `startMessageId` value, we can't get any message > > Sometimes we want to read the message id 4 for the first time, we have > only one approach in client: > > ``` > Reader<byte[]> reader = pulsarClient.newReader() > .topic(topicName) > .subscriptionName(subscriptionName) > .startMessageId(MessageId.latest) > .startMessageIdInclusive() > .create(); > > reader.hasMessageAvailable(); > Message<byte[]> msg = reader.readNext(1, TimeUnit.SECONDS); > ``` > > Call `reader.hasMessageAvailable()` before `reader.readNext()` can get the > correct message id 4, which include seek action when the > `startMessageIdInclusive()` is enabled. > > This approach is confusing. If we do this on the broker side, it will > make things easier. > > ## Goal > > This PIP proposes support for reading the message of `startMessageId` > position on the broker side: > > - Add to `Consumer` > - Add to `Reader` > > ## Implementation > > ### Protocol > > Add a `start_message_id_inclusive` field to `CommandSubscribe` for > determine whether to read the message of `startMessageId` position: > > ``` > message CommandSubscribe { > // some fields > > // If specified, the subscription will read the message from the start > message id position. > optional bool start_message_id_inclusive = 20 [default = false]; > } > ``` > > ### ManagedCursorImpl > > Add a check in > `org.apache.bookkeeper.mledger.impl.ManagedCursorImpl#initializeCursorPosition`. > > > We only need to care that the `startMessageId` is `MessageId.latest` and > the`start_message_id_inclusive` is `true`, we get latest position from > ledger as `readPosition` value, otherwise if > the`start_message_id_inclusive` is `false`, get next position of the > latest position as `readPosition` value. > > ### Client > > The `Consumer` and `Reader` support setting the > `start_message_id_inclusive` value to `CommandSubscribe` command. > > ### Compatibility > > This feature can have both backward and forward compatibility, this means > the users can use any client to request any broker. > > Notice that the users still can read the message of the latest position by > call `reader.hasMessageAvailable()` before `reader.readNext()`, but this > call can be ignored when using the new client and the new broker. >
