sijie/pip-5.md

## pip-5.md

      
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              pip-5.md
            
          
Status: Initial Draft
Discussion Thread: N/A
Issue: #xxx

Motivation

In use cases such as streaming processing, they need a timestamp in messages to process. This timestamp is called event time,
which is different from publish time - the timestamp that this even occurs. The event time is typically provided and set
by the applications.
To solve these use cases, we propose to add a event time for pulsar messages.
Changes

Public Interfaces


add a method #setEventTime(long timestamp) in MessageBuilder.java

/**
 * Set the event time for a given message.
 * <p> Applications can retrieve the event time by calling `Message#getEventTime()`.
 * This field is useful for stream processing.
 * <p> Note: currently pulsar doesn't support event-time based index. so the subscribers can't
 * seek the messages by event time.
 */
MessageBuilder setEventTime(long timestamp);

add a method #getEventTime() in Message.java

/**
 * Get the event time associated with this event. It is typically set by the applications.
 * <p>If there isn't any event time associated with this event, it will return `-1`.
 */
long getEventTime();
Wire Protocol

we propose to introduce an optional field called event_time in MessageMetadata.
message MessageMetadata {

    ...

    // the timestamp that this event occurs. it is typically set by applications.
    // if this field is omitted, `publish_time` can be used for the purpose of `event_time`.
    optional int32 event_time = 12 [default = -1];

}
Compatibility, Deprecation, and Migration Plan

This change is backward compatible. There is no special migration plan required.
Non Covered

This proposal doesn't cover following areas:

we don't provide any event time index. that means we can't rewind based on event time.