nodece opened a new issue #14883:
URL: 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.
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