nodece commented on code in PR #21873:
URL: https://github.com/apache/pulsar/pull/21873#discussion_r1448935171
##########
pip/pip-330.md:
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@@ -0,0 +1,43 @@
+# PIP-330: getMessageById gets all messages
+
+# Motivation
+
+The `org.apache.pulsar.client.admin.Topics` provides
`getMessageById(java.lang.String, long, long)` method to get the
+message, which returns one message. If the message id refers to a batch
message, we only can get the first message, not
+all messages.
+
+This behavior affects our analysis of messages by the message id.
+
+# Goals
+
+## In Scope
+
+Add a method that returns all messages by message id to the
`org.apache.pulsar.client.admin.Topics` interface.
+
+# Detailed Design
+
+## Design & Implementation Details
+
+Add `getMessageById(java.lang.String, java.lang.String)` to
`org.apache.pulsar.client.admin.Topics` interface:
+
+```java
+public interface Topics {
+ List<Message<byte[]>> getMessageById(String topic, String messageId)
throws PulsarAdminException;
Review Comment:
> It seems like you can retain the exact signature we have today:
>
> ```
> public Message<byte[]> getMessageById(String topic, long ledgerId, long
entryId)
> ```
I should add `@Deprecate` for `public Message<byte[]> getMessageById(String
topic, long ledgerId, long entryId)`.
We need to consider the batch message(msg1, msg2, msg3), when you use the
method, you can only get the `msg1`, not all. This will create a false
impression that the user thinks there is only one message.
> and perhaps change the name to signify you will get _all_ messages:
>
> ```
> public Message<byte[]> getAllMessagesById(String topic, long ledgerId,
long entryId)
> ```
>
> and you can add to get a specific one, by the batch index:
>
> ```
> public Message<byte[]> getMessageById(String topic, long ledgerId, long
entryId, long batchIndex)
> ```
I prefer to `public Message<byte[]> getMessageById(String topic, long
ledgerId, long entryId, long batchIndex)`, when batchIndex is greater than -1,
we can extract the specific one from the batch message by batchIndex.
The current discussion point is whether we should use a `String` parameter
or multiple parameters(`long ledgerId, long entryId, long batchIndex`). IMO,
everything is fine.
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