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https://issues.apache.org/jira/browse/CASSANDRA-15066?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16801276#comment-16801276
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Aleksey Yeschenko commented on CASSANDRA-15066:
-----------------------------------------------
There are two improvements responsible for a large number of files touched,
that might make the change set seem scarier than it is - despite most of the
files affected in a very minor, mechanical way. One of them is the merge of
{{MessageIn}} and {{MessageOut}} into single {{Message}} class; the other is
the improvements to {{Verb}} enum.
{{MessageIn}} and {{MessageOut}} classes are almost exact duplicates of each
other, except {{MessageOut}} has no {{id}} field. Folding them into one class
allowed to both get rid of this duplication, and to place ser/deser logic next
to each other, in a single {{Serializer}} class, as it always should’ve been -
reducing the risk of people forgetting to update one half but not the other.
{{Verb}} was improved in multiple ways. Firstly, we realized that important
information was unnecessarily detached from Verb class. Namely,
{{DROPPABLE_VERBS}} {{EnumSet}}, {{verbStages}} {{EnumMap}},
{{verbSerializers}} {{EnumMap}}, and {{callbackDeserializers}} {{EnumMap}} in
{{MessagingService}}. Now everything is properly encapsulated in {{Verb}}
fields. Secondly, we introduced matching response verbs for every request verb,
replacing the single {{REQUEST_RESPONSE}} verb. Doing this allowed us to make
deserialization of {{Message}} no longer rely on global state (callbacks
expiring map). Thirdly, to allow cleaning up serialization logic further, we
introduced a dedicated {{FAILURE_RSP}} verb to replace {{FAILURE_RESPONSE}} and
{{FAILURE_REASON}} parameter types. As a result of all this, {{Verb}} bulked up
a little and was promoted to a non-inner class of its own.
While there, we also made a small semantic change. Having a separate set of
droppable verbs made every newly introduced verb implicitly undroppable by
default. This led, over the years, to multiple verbs being made undroppable by
omission - sometimes those that don’t even have a callback attached to them.
Additionally, no verb in Cassandra has ever been truly droppable - as this is
simply not a guarantee we can physically provide. So we replaced the concept
with explicit longish timeouts instead - rpc timeout or 5 minutes, whichever is
longer.
Other minor improvements to {{Verb}} and {{Message}}, in no particular order:
- {{flags}} field was introduced to replace all effectively-boolean parameters
that were previously wastefully serialized as {{ONE_BYTE}}
({{FAILURE_RESPONSE}}, {{FAILURE_CALLBACK}}, and {{TRACK_REPAIRED_DATA}})
- {{Verb}} is serialized as unsigned vint instead of 4-byte int
- {{PROTOCOL_MAGIC}} bytes are gone (see the comment on framing and CRC)
- params are serialized more efficiently now:
** param name uses {{ParamType}} ordinal instead of encoding {{ParamType}}
name as a utf8 string
** we switched back to encoding param count rather than param byte length - so
on read we don’t need to allocate extra byte arrays and {{DataInputBuffer}},
and on write to avoid unnecessary garbage in {{DataOutputBuffer}} to
pre-calculate serialized size
When combined, the changes to these two classes are responsible for a large
number of files touched (class renames and import changes), but they are
mechanical and not a risk. But we strongly believe that cleanup like this is
important and needs to happen, or else we’ll forever drown in technical debt.
> Improvements to Internode Messaging
> -----------------------------------
>
> Key: CASSANDRA-15066
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15066
> Project: Cassandra
> Issue Type: Improvement
> Components: Messaging/Internode
> Reporter: Benedict
> Assignee: Benedict
> Priority: Normal
> Fix For: 4.0
>
>
> CASSANDRA-8457 introduced asynchronous networking to internode messaging, but
> there have been several follow-up endeavours to improve some semantic issues.
> CASSANDRA-14503 and CASSANDRA-13630 are the latest such efforts, and were
> combined some months ago into a single overarching refactor of the original
> work, to address some of the issues that have been discovered. Given the
> criticality of this work to the project, we wanted to bring some more eyes to
> bear to ensure the release goes ahead smoothly. In doing so, we uncovered a
> number of issues with messaging, some of which long standing, that we felt
> needed to be addressed. This patch widens the scope of CASSANDRA-14503 and
> CASSANDRA-13630 in an effort to close the book on the messaging service, at
> least for the foreseeable future.
> The patch includes a number of clarifying refactors that touch outside of the
> {{net.async}} package, and a number of semantic changes to the {{net.async}}
> packages itself. We believe it clarifies the intent and behaviour of the
> code while improving system stability, which we will outline in comments
> below.
> https://github.com/belliottsmith/cassandra/tree/messaging-improvements
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