Cancel query evaluation

[GoogleCodeExporter]

It should be possible to stop the evaluation of long-running queries.
To do this we need an additions
- to the REST interface and
- to the WebUI to cancel query evaluation and we need to be able
- to keep the runtime from using more resources after the query has been 
cancelled.
We also need to decide, if we also want to interrupt statements that change the 
database (I think we should do this as well, but we need to be specify the 
transacional semantics of this).

Original issue reported on code.google.com by westm...@gmail.com on 10 Jun 2013 at 5:06

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Original comment by westm...@gmail.com on 21 Jun 2013 at 10:11

• Added labels: Severity-PostBeta

[GoogleCodeExporter]

Issue 519 has been merged into this issue.

Original comment by westm...@gmail.com on 21 Jun 2013 at 10:11

[GoogleCodeExporter]

The transactional semantics (replying to Till) are "easy" - we can handle it as 
though a failure occurred (caused by cancellation) and use our "existing 
semantics" as the answer.  I.e., whatever's happened up to then has happened, 
if the entity-level transactions have committed, and what remains has not.  
It's then an orthogonal issue whether or not those are "good semantics" - but 
this, to me, seems like a reasonable approach.

We could add a Cancel entry point to the REST/HTTP API for async queries - it 
would look just like the status entry point, but would kill the job.

We could then change the WebUI to always use async execution for queries, as it 
would then always get a handle back for a long query.  (By "always" I mean with 
very high probability; obviously there could be certain killer failure combos 
where that did not happen.)

Original comment by dtab...@gmail.com on 23 Jun 2013 at 7:17