[CASSANDRA-12920] Possible messaging latency caused by not flushing in time

• Type: Bug
• Status: Resolved
• Priority: Low
• Resolution: Not A Problem
• Fix Version/s: 2.2.5
• Severity: Low
• Assignee: Simon Zhou
• Reporter: Simon Zhou

Authors

Simon Zhou

Reviewers

Ariel Weisberg

• Created: 17/Nov/16 04:15
• Updated: 16/Apr/19 09:30
• Resolved: 17/Nov/16 18:20

Description

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.

 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