Hi,
I've been looking into the following issue:
"Whenever performing a stress test on a Geode cluster and forcefully killing
one of the members, all the threads in the application get stuck".
To give more context these are the conditions under the test is performed:
* A cluster is deployed with:
* 2 locators.
* 3 servers.
* 2 partitioned regions are created and collocated with a third one (from
now on called the "anchor").
* Also, regions have a single redundant copy configured.
* Whether or not to enable persistence on these regions do not affect to
the test outcome.
* Note that we've configured a PartitionResolver for both of these
regions.
* A geode-native test application is spin up with 20 threads sending a pack
of 1 put request to each of the partitioned
regions regions (except for the "anchor"), all of that within a transaction.
See example below to illustrate the kind of traffic sent:
void thread() {
while(true) {
common_prefix = to_string(time(nullptr));
tx_manager->begin();
for(region_name : {"region_a", "region_b"}) {
key = "key-" + common_prefix + "|" + to_string(rand());
value = to_string(rand());
cache->getRegion(region_name)->put(key, value);
}
tx_manager->commit();
}
}
The test consists of:
* Spinning up the cluster.
* Running the application.
* One of the servers (from now on called "server-0") is forcefully
restarted by
using kill -KILL <PID> and after that starting it up again with gfsh.
The expectation of this test is that given that data has a redundant copy, and
we have 2 servers up and running all the time, then writing data should be
handled smoothly.
However, what actually happens is that all application threads end up being
stuck.
So, in the process of troubleshooting, we noticed that there was several
dead-locks in the geode-native client, which resulted in the following PRs:
* https://github.com/apache/geode-native/pull/660
* https://github.com/apache/geode-native/pull/676
* https://github.com/apache/geode-native/pull/699
After solving all dead-locks in the client-side, we were still noticing the
same outcome in the test.
So, after more digging, there it is what we noticed:
* Once the server is killed, geode-native removes the server endpoint from
the ClientMetadataService.
* But given that put requests can be only executed on the server holding
the primary copy, these requests ended up being proxied towards the server that
was just killed.
* As it takes some time for the cluster members to notice that other
members are down, requests proxied trough "healthy" servers take longer than
expected. Something between 5-30 seconds.
* So, in the end, all the threads are stuck for this interval of time
because the server they are contacting, are contacting "server-0".
For the sake of clarity I've attached a diagram demonstrating the test
scenario. Let me know any additional clarifications you might need to
understand the test itself.
And now, my questions here are:
* Have you encountered this behavior before? And if so, how did you solved
that?
* Is this expected behavior? And if so, what's the point of having a
cluster of several members with partitioned redundant data?
Sorry for the long reading and thanks for any help you can throw in.
BR,
Mario.
