<div dir="ltr">Thanks for the file. Looking at it, I've found several threads waitin on lock 0x00000005e23c2028. Do a search for this value and you'll find them.<div><br></div><div>Looking at other threads, I can also tell that the system was in the middle of a flush operation. Thread 0x00007f1b34146000 is currently flushing obsolete catalogs. This same thread owns the lock on the schema pool. It's a deadlock. </div><div><br></div><div> - Thread A tries to clear the cache of some elements. It first acquires a lock on the schema pool. </div><div> - Thread A then sends a message to the Actor to do the actual flush, so it waits for an answer.</div><div> - Thread B, the Actor, in the meanwhile, receives an external event. To process it, it needs a lock on the pool.</div><div><br></div><div>That's unfortunate timing. We'll need to think about how to fix this correctly. Please file a Jira bug with as much information as you can. If you can share some of the thread snippets, that's also useful to confirm our tests.</div><div><br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Mar 30, 2016 at 11:27 AM, Luc Boudreau <span dir="ltr"><<a href="mailto:lucboudreau@gmail.com" target="_blank">lucboudreau@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><br></div>Your description is exact. <div><br></div><div>I'm a little surprised that no other threads are waiting on that lock. Would you mind sharing the full thread dump? Maybe privately?</div></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Mar 30, 2016 at 11:21 AM, Wright, Jeff <span dir="ltr"><<a href="mailto:jeff.s.wright@truvenhealth.com" target="_blank">jeff.s.wright@truvenhealth.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d">There are no other threads waiting on the same monitor. I have 5 thread dumps from 5 different app servers, and all of them have this same pattern. There are
two Actor threads, one of the Actor threads is blocked on getRolapSchemas() and no other thread references the same monitor.
<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d">From your description, here’s how I imagine things to work with a 5 node cluster and a distributed cache... If a user runs MDX against CatalogA on Node1, the
results of that query will get added to the distributed segment cache on Node1. The distributed cache will send an event to Nodes 2-5. That event will allow Nodes 2-5 to index the new segments. Indexing will force CatalogA to be loaded on Nodes 2-5, if it’s
not already loaded. Is that right?<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d">--jeff<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <a href="mailto:mondrian-bounces@pentaho.org" target="_blank">mondrian-bounces@pentaho.org</a> [mailto:<a href="mailto:mondrian-bounces@pentaho.org" target="_blank">mondrian-bounces@pentaho.org</a>]
<b>On Behalf Of </b>Luc Boudreau<br>
<b>Sent:</b> Wednesday, March 30, 2016 10:34 AM<br>
<b>To:</b> Mondrian developer mailing list <<a href="mailto:mondrian@pentaho.org" target="_blank">mondrian@pentaho.org</a>><br>
<b>Subject:</b> Re: [Mondrian] hanging application: segment cache manager and schema load?<u></u><u></u></span></p><div><div>
<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">This stack tells us that the Actor has received a notification from an external event. A new segment must be indexed. The Actor is waiting on the RolapSchemaPool to free up so that it can grap a Star instance and pin the segment.<u></u><u></u></p>
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<p class="MsoNormal">What other threads are waiting on that same monitor? (<span style="font-size:11.0pt;font-family:"Calibri",sans-serif">0x00007f1ad965f000)</span><u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">On Wed, Mar 30, 2016 at 9:14 AM, Wright, Jeff <<a href="mailto:jeff.s.wright@truvenhealth.com" target="_blank">jeff.s.wright@truvenhealth.com</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">We’ve seen our application hang a couple times. Looking at thread dumps, I’m suspicious of this excerpt:<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">"mondrian.rolap.agg.SegmentCacheManager$ACTOR" daemon prio=10 tid=0x00007f1b34170000 nid=0xf25 waiting for monitor entry [0x00007f1ad965f000]<u></u><u></u></p>
<p class="MsoNormal"> java.lang.Thread.State: BLOCKED (on object monitor)<u></u><u></u></p>
<p class="MsoNormal"> at mondrian.rolap.RolapSchemaPool.getRolapSchemas(RolapSchemaPool.java:420)<u></u><u></u></p>
<p class="MsoNormal"> - waiting to lock <0x00000005e23c2028> (a mondrian.rolap.RolapSchemaPool)<u></u><u></u></p>
<p class="MsoNormal"> at mondrian.rolap.RolapSchema.getRolapSchemas(RolapSchema.java:930)<u></u><u></u></p>
<p class="MsoNormal"> at mondrian.rolap.agg.SegmentCacheManager.getStar(SegmentCacheManager.java:1621)<u></u><u></u></p>
<p class="MsoNormal"> at mondrian.rolap.agg.SegmentCacheManager$Handler.visit(SegmentCacheManager.java:661)<u></u><u></u></p>
<p class="MsoNormal"> at mondrian.rolap.agg.SegmentCacheManager$ExternalSegmentCreatedEvent.acceptWithoutResponse(SegmentCacheManager.java:1222)<u></u><u></u></p>
<p class="MsoNormal"> at mondrian.rolap.agg.SegmentCacheManager$Actor.run(SegmentCacheManager.java:1019)<u></u><u></u></p>
<p class="MsoNormal"> at java.lang.Thread.run(Thread.java:724)<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">I don’t fully understand SegmentCacheManager, but based on Julian’s 2012 blog post I get the impression the Actor thread is supposed to run very. If that corresponds to the stack
trace above, that’s a big problem - we see schema loads take minutes.<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">I also see that there were some code changes in August last year for MONDRIAN-2390, to make locking for schema load lower level. We don’t have that code.<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">Btw we have a distributed cache.<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">Does it sound like I’m on to a problem in our environment? Maybe even a general problem?<u></u><u></u></p>
<p class="MsoNormal"><span style="color:#888888"> <u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#888888">--Jeff Wright<u></u><u></u></span></p>
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