[jira] [Created] (HBASE-16577) On reducing the log level of *TooSlow log lines

["Andrew Purtell (JIRA)" <ji...@apache.org>]

Andrew Purtell created HBASE-16577:
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             Summary: On reducing the log level of *TooSlow log lines
                 Key: HBASE-16577
                 URL: https://issues.apache.org/jira/browse/HBASE-16577
             Project: HBase
          Issue Type: Brainstorming
            Reporter: Andrew Purtell


I was looking at the nature and distribution of responseTooSlow messages on our clusters. The majority of responseTooSlow warnings are for Scan or Multi. 

Scans may take a long time to return. It will totally depend on how much data is in the table, how the data is distributed, and the range and selectivity of the query. We are not measuring response time in a way to know what is proportionate to the work requested. Another problematic example is Multi. We don't get valid results considering a multi with 1 op and a multi with 100 ops to be equivalent as far as being "too slow". 

If we aggressively filter responseTooSlow messages to just include the ops we can expect to be small, constant, request-independent units of work, this leaves us with Get and Mutate. This gives us no more information then we get from the Canary with read and write checks turned on. The Canary issues Get and Mutate ops and, better, measures availability and latency from the client perspective. 
 
Where I end up is I think my shop should ignore responseTooSlow as signal as being far too noisy. The trouble then is it is logged at WARN level. This implies there is something wrong that needs to be fixed. That may not be the case. It's going to require some analysis of the application and the request particulars extracted from the log line. WARN seems inappropriate for this type of indication. There's nothing (necessarily) wrong with HBase, or the app. Should be logged at more like INFO. 

Furthermore the response might not be too slow, so calling it "responseTooSlow" isn't quite right. More like "responseMaybeSlow" :-)



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