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cloudera / impyla

Python DB API 2.0 client for Impala and Hive (HiveServer2 protocol)
Apache License 2.0
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Killing SQL queries #178

Open julienbaley opened 8 years ago

julienbaley commented 8 years ago

Is it a feature that could be added to impyla, or is there no way to do that?

I've tried to use Cursor.cancel_operation, but it didn't seem to do anything. In fact, I've found that Cursor.execute_async was not returning immediately (it basically behaved like execute). Is this a known problem? Do I need some extra configuration?

(I'm using Hive 2 and Python 3.4)

wesm commented 8 years ago

@julienbaley this was just fixed in https://github.com/cloudera/impyla/commit/1253050fc98e076465cd52a8e1c35d4eff731477

Can you confirm if this solved your problem (I'm going to cut a release next week)

julienbaley commented 8 years ago

Ah, I should have installed master! I used the latest version from pip and then looked through the code that was already fixed. I'll have to try on Monday first thing and I'll let you know. Thanks

julienbaley commented 8 years ago

@wesm : it's now working, indeed, thanks :) There was a problem with fetch* methods not blocking, I've sent a PR #180 Could you ping me when you make a new release?

wesm commented 8 years ago

This fix was released

julienbaley commented 8 years ago

@wesm Out of curiosity, why have you guys stopped using Git tags / GitHub releases? It makes it difficult to read what's in what release..

wesm commented 8 years ago

Sorry about that. I just pushed a 0.13.5 tag. The others were mostly bumping dependencies (plus 0.13.4 contained a packaging hiccup that required bumping the release number to push a new tarball)

julienbaley commented 8 years ago

@wesm I guess I should just reopen this one. It is now possible to kill queries, but not in a satisfying way: I create a cursor and call execute_async on it. In another thread, I call cancel_operation on the same cursor. This doesn't run gracefully, and both execute_async and cancel_operation raise exceptions. While I could expect the execute_async to raise one, I don't see why cancel_operation does.

Is that not what cancel_operation is for? I haven't found how I'm supposed to use it otherwise.

wesm commented 8 years ago

Is cancel_operation being called before execute_async has been completed? Sounds like there may be a threadsafety issue (may need to add a lock to the Cursor object)

julienbaley commented 8 years ago

I'm calling it after. Do I misunderstand the name of the function? From the name, I take cancel_operation to allow me to kill a running query (which it does, but raises exceptions on both ends). This is very useful if the user realises that their query is going to take an entire day to complete because e.g. they forgot the WHERE clause.

wesm commented 8 years ago

Could you break this down more concretely, I'm still not 100% clear on what is happening. it sounds like:

Is that not the case? Or can you explain where execute_async is failing? I don't understand what "raises exceptions on both ends" means.

If execute_async fails, then it may not be appropriate to call cancel_operation (which relies on execute_async having been successful)

If I'm misunderstanding can you please give more detail on the exact control flow and the stack traces. Thank you

julienbaley commented 8 years ago

Sure, here is what I run: Thread 1: cur.execute_async(sql) # runs for hours Thread 2 (while Thread 1 is running) : cur.cancel_operation # triggered by the user in a web UI, when they realise their query in thread 1 is going to make the server crash. The goal is to make Hive stop running the query in Thread 1. (does this make sense?)

(I'm not at work so I can't check, but from memory) Thread 1 raises a ThriftProtocolException(type=4). Thread 2 raises a HiveServer2Error.

Of course, if it happens just because I'm using cancel_operation for something it's not intended for, then fine, I can just catch the exceptions and it's ok.

wesm commented 8 years ago

I see. execute_async in theory should not block, so that suggests that the runAsync option of the Thrift request is not working correctly. So this is either a Hive bug or an Impyla bug -- any way you can help debug this further?

julienbaley commented 8 years ago

execute_async is not blocking, as far as I can see (it used to be but that's been fixed a few months ago). I can try to find what's the root of the problem and come back here.