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Explain command forces Quarry to keep running endlessly
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Description

https://quarry.wmflabs.org/query/15594

I started this explain command about 1 day ago. It is still showing as "Running". A number of queries that ran after this one are still shown at Running or Queued.

Event Timeline

I'm still able to run new queries, so at least this doesn't seem to be disruptive for other users. Or do we have reasons to believe it is?

AFAIK, queries are automatically killed after some time.

About a dozen or more queries that happened just after this query are still marked as "Running". I believe there are others as well, some more queries that followed these.

https://quarry.wmflabs.org/query/runs/all?limit=100&from=15350

I think somehow running Explain caused all queries that followed to pile up and never actually be run. But without actually getting killed.

See https://quarry.wmflabs.org/query/15607 for an example

Just wanted to point out that 4 months later, the queries are still running.

I think what the interface says isn't necessarily true.

Explain is almost certainly broken by T264254: Prepare Quarry for multiinstance wiki replicas

The functionality will need rewriting or similar. It stopped working reliably long before that though because of load balancing on the replicas.