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https://issues.apache.org/jira/browse/IMPALA-8532?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tim Armstrong updated IMPALA-8532:
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Component/s: Frontend
> Query Plan Page Fails When Profile is Large
> -------------------------------------------
>
> Key: IMPALA-8532
> URL: https://issues.apache.org/jira/browse/IMPALA-8532
> Project: IMPALA
> Issue Type: Bug
> Components: Frontend
> Reporter: Alan Jackoway
> Priority: Major
>
> We discovered that on queries with large profiles, the query plan page with
> the boxes fails to load.
> In Chrome, we saw an increasing number of backend XHR requests, and this JS
> error:
> {quote}
> Uncaught SyntaxError: Unexpected end of JSON input
> at JSON.parse (<anonymous>)
> at XMLHttpRequest.renderGraph
> (query_plan?query_id=ec422d433862a401:5b5855a700000000:232)
> {quote}
> Our backend requests to the retrieve the plan JSON were returning 1.5MB in
> between 1.5 and 4 seconds.
> I believe the issue is that the code is set up like this:
> {code}
> function renderGraph(ignored_arg) {
> if (req.status != 200) return;
> var json = JSON.parse(req.responseText);
> // Doesn't get here
> ...
> }
> ...
> // Called periodically, fetches the plan JSON from Impala and passes it to
> renderGraph()
> // for display.
> function refresh() {
> req = new XMLHttpRequest();
> req.onload = renderGraph;
> req.open("GET",
> "/query_plan?query_id=ec422d433862a401:5b5855a700000000&json", true);
> req.send();
> }
> // Force one refresh before starting the timer.
> refresh();
> setInterval(refresh, 1000);
> {code}
> The issue is that req variable is in global scope. If it takes more than one
> second to fulfill the request, {{setInterval}} has run again and replaced the
> req variable with a new one that is running. Then in the renderGraph step,
> either status = 0 (because the variable is new) or the data gets cut off and
> fails to load. I saw both happening pretty regularly, with no obvious pattern
> between status=0 and status=200 but data being incomplete.
> Some options I see to fix it:
> * Change scope of the req variable so that renderGraph always gets the
> request that is complete rather than the most recent request created
> * replace setInterval with an approach that kicks off the new request only
> when the previous request is complete.
> This should be easy to reproduce if you can generate a plan that takes > 1
> second to return from your impalad to your browser.
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