GitHub user davek2 opened a pull request:
https://github.com/apache/kafka/pull/1419
Allocate 2 attribute bits to signal payload format
This documentation update proposes a mechanism to signal the serialization
used for the message payload, resolving issue
https://issues.apache.org/jira/browse/KAFKA-3744. No change is made to the
message structure; two previously-reserved bits in the attribute byte now have
defined values, and for one of four cases the key field is defined to be a JSON
object.
No change is required to messaging software. No change is required to
existing producer and consumer clients that use pre-agreed payload
serialization.
Misc notes:
1) Only one attribute bit would be needed if serialization were always
signalled using the key field. But it seems preferable to define two common
serializations that do not have any dependency on the key field. Selection of
the common formats is arbitrary; text and avro seem reasonable but any two
could be used instead.
2) The compression attribute uses three bits but only two are defined. If
the intent is to use all three bits for compression the undefined values should
be listed as reserved; if not, the timestamp attribute can slide down to bit 2
and serialization to bits 3~4, leaving bits 5~7 reserved.
3) It's unclear why message field 6 should be called "key" - a
variable-length field is more likely to be described as "attributes" or
"metadata", and 1-byte field 3 would be called "flags" instead of "attributes".
4) Field 8 is called "payload" under message format and "value" under
on-disk format. Changed to payload in both places.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/davek2/kafka trunk
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/kafka/pull/1419.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #1419
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commit 1d88b8d48cdfe67989bebf239f7588ca24e961b6
Author: Joe <dav...@hotmail.com>
Date: 2016-05-24T00:32:04Z
Allocate 2 attribute bits for payload format
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