Canceling a (long-running) query

[henningsway]

I use the implyr-package frequently. Sometimes I realize only after I have sent a query, that it will take (too) long to take the results.

I havent yet found the best way to cancel a query. The Stop-button in Rstudio doesn't do the trick, same with Ctrc-c. I sometimes terminate Rstudio or Rstudio Server, if a query takes too long.

What are the mechanics that make it difficult to cancel a query? What approach would you suggest?

[ianmcook]

Thanks for asking about this. Cancelling queries is a tricky problem because of how the stack of packages that support implyr works. The odbc package, for example, runs C++ code that can't or doesn't check for interrupts from R.

There are possible workarounds for this, for example, we could implement an alternative version of the collect() function that would work asynchronously and would check often for interrupts or cancel commands.

Do these long waits typically happen after you've executed a collect() command? Or in some other situation?

[henningsway]

It depends. It does often happen after I sent a collect(), but also , when I work with a remote tbl, want to see the output of some sql-transformations and underestimated the time the computation of the preview takes. ;-)

I would guess that both cases happen about equally often. (Though for the second one, I could also try to develop on much smaller subset more often.)

[henningsway]

I think something similar has been implemented for sparklyr recently: https://blog.rstudio.com/2018/10/01/sparklyr-0-9/