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https://issues.apache.org/jira/browse/HBASE-22978?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16930921#comment-16930921
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Andrew Purtell commented on HBASE-22978:
----------------------------------------
Shell is ring buffers. This is an online slow request log. The goal isn’t to
have complete history it is to keep a list of interesting events for as long as
we can without consuming too many resources either RAM or files.
Having an option also to dump to HDFS is important so we added that as a side
goal. The tool that dumps the files will have the same capabilities as the
shell because I expect to share common utility classes. However this is not the
main goal. The main goal is shell access to ring buffers containing *latest*
events of interest, for use in online and active debugging.
> Online slow response log
> ------------------------
>
> Key: HBASE-22978
> URL: https://issues.apache.org/jira/browse/HBASE-22978
> Project: HBase
> Issue Type: New Feature
> Components: Admin, Operability, regionserver, shell
> Reporter: Andrew Purtell
> Priority: Minor
>
> Today when an individual RPC exceeds a configurable time bound we log a
> complaint by way of the logging subsystem. These log lines look like:
> {noformat}
> 2019-08-30 22:10:36,195 WARN [,queue=15,port=60020] ipc.RpcServer -
> (responseTooSlow):
> {"call":"Scan(org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ScanRequest)",
> "starttimems":1567203007549,
> "responsesize":6819737,
> "method":"Scan",
> "param":"region { type: REGION_NAME value:
> \"tsdb,\\000\\000\\215\\f)o\\\\\\024\\302\\220\\000\\000\\000\\000\\000\\001\\000\\000\\000\\000\\000\\006\\000\\000\\000\\000\\000\\005\\000\\000<TRUNCATED>",
> "processingtimems":28646,
> "client":"10.253.196.215:41116",
> "queuetimems":22453,
> "class":"HRegionServer"}
> {noformat}
> Unfortunately we often truncate the request parameters, like in the above
> example. We do this because the human readable representation is verbose, the
> rate of too slow warnings may be high, and the combination of these things
> can overwhelm the log capture system. The truncation is unfortunate because
> it eliminates much of the utility of the warnings. For example, the region
> name, the start and end keys, and the filter hierarchy are all important
> clues for debugging performance problems caused by moderate to low
> selectivity queries or queries made at a high rate.
> We can maintain an in-memory ring buffer of requests that were judged to be
> too slow in addition to the responseTooSlow logging. The in-memory
> representation can be complete and compressed. A new admin API and shell
> command can provide access to the ring buffer for online performance
> debugging. A modest sizing of the ring buffer will prevent excessive memory
> utilization for a minor performance debugging feature by limiting the total
> number of retained records. There is some chance a high rate of requests will
> cause information on other interesting requests to be overwritten before it
> can be read. This is the nature of a ring buffer and an acceptable trade off.
> The write request types do not require us to retain all information submitted
> in the request. We don't need to retain all key-values in the mutation, which
> may be too large to comfortably retain. We only need a unique set of row
> keys, or even a min/max range, and total counts.
> The consumers of this information will be debugging tools. We can afford to
> apply fast compression to ring buffer entries (if codec support is
> available), something like snappy or zstandard, and decompress on the fly
> when servicing the retrieval API request. This will minimize the impact of
> retaining more information about slow requests than we do today.
> This proposal is for retention of request information only, the same
> information provided by responseTooSlow warnings. Total size of response
> serialization, possibly also total cell or row counts, should be sufficient
> to characterize the response.
> Optionally persist new entries added to the ring buffer into one or more
> files in HDFS in a write-behind manner. If the HDFS writer blocks or falls
> behind and we are unable to persist an entry before it is overwritten, that
> is fine. Response too slow logging is best effort. If we can detect this make
> a note of it in the log file. Provide a tool for parsing, dumping, filtering,
> and pretty printing the slow logs written to HDFS. The tool and the shell can
> share and reuse some utility classes and methods for accomplishing that.
> —
> New shell commands:
> {{get_slow_responses [ <server1> ... , <serverN> ] [ , \{ <filter-attributes>
> } ]}}
> Retrieve, decode, and pretty print the contents of the too slow response ring
> buffer maintained by the given list of servers; or all servers in the cluster
> if no list is provided. Optionally provide a map of parameters for filtering
> as additional argument. The TABLE filter, which expects a string containing a
> table name, will include only entries pertaining to that table. The REGION
> filter, which expects a string containing an encoded region name, will
> include only entries pertaining to that region. The CLIENT_IP filter, which
> expects a string containing an IP address, will include only entries
> pertaining to that client. The USER filter, which expects a string containing
> a user name, will include only entries pertaining to that user. Filters are
> additive, for example if both CLIENT_IP and USER filters are given, entries
> matching either or both conditions will be included. The exception to this is
> if both TABLE and REGION filters are provided, REGION will be preferred and
> TABLE will be ignored. A server name is its host, port, and start code, e.g.
> "host187.example.com,60020,1289493121758".
> {{clear_slow_responses [ <server1> ... , <serverN> ]}}
> Clear the too slow response ring buffer maintained by the given list of
> servers; or all servers on the cluster if no argument is provided. A server
> name is its host, port, and start code, e.g.
> "host187.example.com,60020,1289493121758".
> —
> New Admin APIs:
> {code:java}
> List<ResponseDetail> Admin#getSlowResponses(@Nullable List<String> servers);
> {code}
> {code:java}
> List<ResponseDetail> Admin#clearSlowResponses(@Nullable List<String> servers);
> {code}
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