The EVENT macro is specific to open telemetry tracing. So if `side`
is only used to populate the event then I think you will need to
surround the entire block with:
```
#ifdef ARROW_WITH_OPENTELEMETRY
int side = ...
EVENT(span_, "InputReceived", {{"batch.length", batch.length}, {"side",
side}});
#endif
```
If you want to see it in action then you can enable open telemetry by
turning on ARROW_WITH_OPENTELEMETRY in the cmake options. However, to
actually get output you will need to tell OT where to send output.
The simplest way to do this is to use the ARROW_TRACING_BACKEND
environment variable. You can see all the options we have at the
moment in src/arrow/util/tracing_internal.cc but a simple choice is
"ostream" which dumps everything to (I think) stdout.
Example:
```
ARROW_TRACING_BACKEND=ostream ./debug/arrow-dataset-scanner-test \
--gtest_filter=TestScannerThreading/TestScanner.FilteredScanNested/2Threaded1d1b1024r
```
Yields something like:
```
{
name : SinkNode:
trace_id : 1e39508fe9fe74bfc1c39cfbe9b63d55
span_id : afb1b87450748124
tracestate :
parent_span_id: 4b46e64fb1469f90
start : 1650385199799132739
duration : 9878711
description :
span kind : Internal
status : Unset
attributes :
thread.id: 140287607824768
node.detail: :SinkNode{}
node.kind: SinkNode
node.label:
events :
{
name : InputFinished
timestamp : 1650385199804563001
attributes :
batches.length: 1
}
{
name : InputReceived
timestamp : 1650385199807960461
attributes :
batch.length: 512
}
links :
resources :
service.name: unknown_service
telemetry.sdk.version: 1.3.0
telemetry.sdk.name: opentelemetry
telemetry.sdk.language: cpp
instr-lib : arrow
}
```
To get more complete output from OT you will eventually want to use
the http exporter and export the data to some kind of tool like Jaeger
which can do visualizations of the data and offer flame charts.
On Tue, Apr 19, 2022 at 5:39 AM Li Jin <ice.xell...@gmail.com> wrote:
>
> Hello!
>
> I am trying to implement a new type of join in Arrow Compute engine (asof
> join). I have been looking at code of HashJoinNode and found some debug
> code that seems to be useful:
>
> e.g.:
> EVENT(span_, "InputReceived", {{"batch.length", batch.length}, {"side",
> side}});
>
> But when I try to use similar code in my ExecNode, I got an error:
>
> /home/icexelloss/workspace/arrow/cpp/src/arrow/compute/exec/asof_join_node.cc:67:9:
> error: unused variable ‘side’ [-Werror=unused-variable]
> 67 | int side = (input == inputs_[0]) ? 0 : 1;
> | ^~~~
>
> (here is my code):
> void InputReceived(ExecNode* input, ExecBatch batch) override {
> int side = (input == inputs_[0]) ? 0 : 1;
> EVENT(span_, "InputReceived", {{"batch.length", batch.length}, {"side",
> side}});
> }
>
> I wonder:
> (1) Is there a special cmake flag I need to pass in to enable the EVENT
> marco?
> (2) What does the EVENT marco do and where does it output to?
>
> Thanks!
> Li
