Erick Erickson created SOLR-14861:
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Summary: CoreContainer shutdown needs to be aware of other ongoing
operations and wait until they're complete
Key: SOLR-14861
URL: https://issues.apache.org/jira/browse/SOLR-14861
Project: Solr
Issue Type: Bug
Security Level: Public (Default Security Level. Issues are Public)
Reporter: Erick Erickson
Assignee: Erick Erickson
Noble and I are trying to get to the bottom of the TestBulkSchemaConcurrent
failures and found what looks like a glaring gap in how CoreContainer.shutdown
operates. I don't know the impact on production since we're shutting down
anyway, but I think this is responsible for the errors in
TestBulkSchemaConcurrent and likely behind others, especially any other test
that fails intermittently that involves core reloads, including and especially
any tests that exercise managed schema.
We have clear evidence of this sequence:
1> some CoreContainer.reloads come in and get _partway_ through, in particular
past the test at the top where CoreContainer.reload() throws an AlreadyClosed
exception if (isShutdown).
2> the reloads happening in <1> are interrupted by threads running
CoreContainer.shutdown(), which do at least some processing.
3> the threads in <1> pick back up and go wonky. I suspect that there are a
number of different things that could be going wrong here depending on how far
through CoreContainer.shutdown() gets that pop out in different ways.
Since it's my shift (Noble has to sleep sometime), I put some crude locking in
just to test the idea; incrementing an AtomicInteger on entry to
CoreContainer.reload then decrementing it at the end, and spinning in
CoreContainer.shutdown() until the AtomicInteger was back to zero. With that in
place, 100 runs and no errors whereas before I could never get even 10 runs to
finish without an error. This is not a proper fix at all, and the way it's
currently running there are still possible race conditions, just much smaller
windows. And I suspect it risks spinning forever. But it's enough to make me
believe I finally understand what's happening.
I also suspect that reload is more sensitive than most operations on a core due
to the fact that it runs for a long time, but I assume other operations have
the same potential. Shouldn't CoreContainer.shutDown() wait until no other
operations are in flight?
On a quick scan of CoreContainer, there are actually few places where we even
check for isShutdown, I suspect the places we do are ad-hoc that we've found by
trial-and-error when tests fail. We need a design rather than hit-or-miss
hacking.
I think that isShutdown should be replaced with something more robust. What
that is IDK quite yet because I've been hammering at this long enough and I
need a break.
This is consistent with another observation about this particular test. If
there's sleep at the end, it wouldn't fail; all the reloads get a chance to
finish before anything was shut down.
An open question how much this matters to production systems. In the testing
case, bunches of these reloads are issued then we immediately end the test and
start shutting things down. It needs to be fixed if we're going to cut down on
test failures though. Besides, it's just wrong ;)
Assigning to myself to track. I'd be perfectly happy, now that Noble and I have
done the hard work, for someone to swoop in and take the credit for fixing it ;)
gradlew beast -Ptests.dups=10 --tests TestBulkSchemaConcurrent
always fails for me on current code without my hack...
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