[
https://issues.apache.org/jira/browse/CASSANDRA-12920?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15672738#comment-15672738
]
Ariel Weisberg commented on CASSANDRA-12920:
--------------------------------------------
When count is 1 and the backlog is empty it means it is going to flush on the
last available message. Count is being decremented every iteration of the loop
and will be 1 when the last messages is being written. It's not going to wait
for more messages it's just going to write all available messages and flush
once the last one is being written.
> Possible messaging latency caused by not flushing in time
> ---------------------------------------------------------
>
> Key: CASSANDRA-12920
> URL: https://issues.apache.org/jira/browse/CASSANDRA-12920
> Project: Cassandra
> Issue Type: Bug
> Reporter: Simon Zhou
> Assignee: Simon Zhou
> Priority: Minor
> Fix For: 2.2.5
>
>
> Not sure if this can be improved. We're using Cassandra 2.2.5. Cassandra
> considers messages whose payload size <= 64KB as small messages. For response
> for such as digest request, it's very likely a small message. Even quite a
> few such responses cannot fill in the output buffer and thus trigger a flush.
> One possible issue is that, we use conditions count == 1 && backlog.isEmpty()
> to decide whether to flush the output stream. That means if the backlog is
> empty, we won't flush the output stream even we drained, say, 10 messages
> whose sizes sum < 64K. This may cause delay for small messages. Shouldn't we
> flush after writing the last drained message if backlog is empty? Of course
> if backlog is not empty, we can continue draining more messages and very
> likely trigger a flush very soon.
> Here are some tracing events that show the latency. Be noted that the
> involved nodes are in the same data center whose round trip network latency
> is well below 1ms. Alao we have disabled message coalescing due to
> CASSANDRA-12676.
> {noformat}
> 126571b0-aaa6-11e6-ab2b-77eb6f529c59 | 127c7c28-aaa6-11e6-941f-f3a2e2759bd2
> | Enqueuing response to /*******32.28 |
> *******29.3 | 1199 | SharedPool-Worker-4
> 126571b0-aaa6-11e6-ab2b-77eb6f529c59 | 127cca45-aaa6-11e6-941f-f3a2e2759bd2
> | Sending REQUEST_RESPONSE message to /*******32.28 |
> *******29.3 | 2667 | MessagingService-Outgoing-/*******32.28
> 126571b0-aaa6-11e6-ab2b-77eb6f529c59 | 127cca40-aaa6-11e6-ab2b-77eb6f529c59
> | REQUEST_RESPONSE message received from /*******29.3 |
> *******32.28 | 152635 | MessagingService-Incoming-/*******29.3
> 126571b0-aaa6-11e6-ab2b-77eb6f529c59 | 127cca41-aaa6-11e6-ab2b-77eb6f529c59
> | Processing response from /*******29.3 |
> *******32.28 | 152665 | SharedPool-Worker-45
> 1af31490-aaa6-11e6-ab2b-77eb6f529c59 | 1b08e68a-aaa6-11e6-8dce-951d39203586
> | Enqueuing response to /*******32.28 |
> *******29.5 | 532 | SharedPool-Worker-178
> 1af31490-aaa6-11e6-ab2b-77eb6f529c59 | 1b090d90-aaa6-11e6-8dce-951d39203586
> | Sending REQUEST_RESPONSE message to /*******32.28 |
> *******29.5 | 579 | MessagingService-Outgoing-/*******32.28
> 1af31490-aaa6-11e6-ab2b-77eb6f529c59 | 1b090d90-aaa6-11e6-ab2b-77eb6f529c59
> | REQUEST_RESPONSE message received from /*******29.5 |
> *******32.28 | 143865 | MessagingService-Incoming-/*******29.5
> 1af31490-aaa6-11e6-ab2b-77eb6f529c59 | 1b090d91-aaa6-11e6-ab2b-77eb6f529c59
> | Processing response from /*******29.5 |
> *******32.28 | 143908 |
> SharedPool-Worker-41
> 1af58590-aaa6-11e6-ab2b-77eb6f529c59 | 1b0934a8-aaa6-11e6-8dce-951d39203586
> | Enqueuing response to /*******32.28 |
> *******29.5 | 1632 |
> SharedPool-Worker-159 1af58590-aaa6-11e6-ab2b-77eb6f529c59 |
> 1b0934a9-aaa6-11e6-8dce-951d39203586 | Sending
> REQUEST_RESPONSE message to /*******32.28 | *******29.5 | 1660 |
> MessagingService
> -Outgoing-/*******32.28 1af58590-aaa6-11e6-ab2b-77eb6f529c59 |
> 1b095bb0-aaa6-11e6-ab2b-77eb6f529c59 | REQUEST_RESPONSE
> message received from /*******29.5 | *******32.28 | 129813 |
> MessagingServic
> e-Incoming-/*******29.5 1af58590-aaa6-11e6-ab2b-77eb6f529c59 |
> 1b095bb1-aaa6-11e6-ab2b-77eb6f529c59 |
> Processing response from /*******29.5 | *******32.28 | 129835 |
>
> SharedPool-Worker-3
> 3010cfc0-aaa6-11e6-ab2b-77eb6f529c59 | 3029fd17-aaa6-11e6-a5cc-8b24438aa927
> | Enqueuing response to /*******32.28 |
> *******30.8 | 1686 | SharedPool-Worker-271
> 3010cfc0-aaa6-11e6-ab2b-77eb6f529c59 | 302ae770-aaa6-11e6-a5cc-8b24438aa927
> | Sending REQUEST_RESPONSE message to /*******32.28 |
> *******30.8 | 6938 | MessagingService-Outgoing-/*******32.28
> 3010cfc0-aaa6-11e6-ab2b-77eb6f529c59 | 302ae770-aaa6-11e6-ab2b-77eb6f529c59
> | REQUEST_RESPONSE message received from /*******30.8 |
> *******32.28 | 171380 | MessagingService-Incoming-/*******30.8
> 3010cfc0-aaa6-11e6-ab2b-77eb6f529c59 | 302ae771-aaa6-11e6-ab2b-77eb6f529c59
> | Processing response from /*******30.8 |
> *******32.28 | 171472 | SharedPool-Worker-55
> {noformat}
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
