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From "Matt Stump (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-9193) Facility to write dynamic code to selectively trigger trace or log for queries
Date Mon, 20 Apr 2015 16:07:00 GMT


Matt Stump commented on CASSANDRA-9193:

It's actually pretty simple the Nashorn API makes this pretty easy. For context here is a
little snippet that I had running in {{}}.  I'm evaluating a script, then
executing a named function passing parameters to the JS function. The idea would be to pull
a script from a CF for the injection point, eval and when we reach that point in the code
invoke a known function name adhering to an interface. We would pass the request parameters.
 The JS would have full visibility into the internals of C*.  Each injection point would have
a different context (scope) so that we don't have to worry about namespace collision between

            String script = ""
                            + "var printReadCommands = function(readCommands, consistency,
state) {"
                            + "    for each (var rc in readCommands) {"
                            + "        print(\"rc class definition: \" +
+ \"\\n\");"
                            + "        print(\"KEYSPACE \" + rc.ksName);"
                            + "        print(\" CF \" + rc.cfName);"
                            + "        print(\" KEY \" + rc.key);"
                            + "        print(\"\\n\");"
                            + "    }"
                            + "};";

            Invocable invocable = (Invocable) jsEngine;
            Object result = invocable.invokeFunction("printReadCommands", commands, consistencyLevel,

> Facility to write dynamic code to selectively trigger trace or log for queries
> ------------------------------------------------------------------------------
>                 Key: CASSANDRA-9193
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>            Reporter: Matt Stump
> I want the equivalent of dtrace for Cassandra. I want the ability to intercept a query
with a dynamic script (assume JS) and based on logic in that script trigger the statement
for trace or logging. 
> Examples 
> - Trace only INSERT statements to a particular CF. 
> - Trace statements for a particular partition or consistency level.
> - Log statements that fail to reach the desired consistency for read or write.
> - Log If the request size for read or write exceeds some threshold
> At some point in the future it would be helpful to also do things such as log partitions
greater than X bytes or Z cells when performing compaction. Essentially be able to inject
custom code dynamically without a reboot to the different stages of C*. 
> The code should be executed synchronously as part of the monitored task, but we should
provide the ability to log or execute CQL asynchronously from the provided API.
> Further down the line we could use this functionality to modify/rewrite requests or tasks

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