Hi Pulsar community, I create a PIP for support read the message of `startMessageId` position on the broker side.
The proposal can be found: https://github.com/apache/pulsar/issues/14883 --------- ## 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 and 2: - When we set `earliest` as `strartMessageId` value, we can the message of message id 1 - When we set `latest` as as `strartMessageId` value, we cannot get any message Sometimes we want to read the message id 2 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()`, which can seek to the message id 2, this approach seems confusing. If we do this on the broker side, which will make things easier. ## Goal This PIP proposes support read the message of `startMessageId` position on the broker side. ## 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. --------- Thanks, Zixuan
