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From aaron morton <aa...@thelastpickle.com>
Subject Re: incomplete schema sync for new node
Date Sun, 03 Jul 2011 10:21:43 GMT
First, move off 0.7.2 if you can. While you may not get hit with this  https://github.com/apache/cassandra/blob/cassandra-0.7.6-2/NEWS.txt#L61
you may have trouble with this https://issues.apache.org/jira/browse/CASSANDRA-2554

For background read the section on Staring Up and on Concurrency here http://wiki.apache.org/cassandra/LiveSchemaUpdates

>> java.lang.RuntimeException: java.lang.RuntimeException: Could not reach schema agreement
with /50.0.0.3 in 60000ms

> 
Means you have split brain schemas in the your cluster. use describe cluster in the cli to
see how many versions of the schema you have out there. 

The exception is thrown when the placement strategy (Simple or OldNTS) is trying to calculate
the Natural Endpoints for a Token  (AbstractReplicationStrategy.calculateNaturalEndpoints())
. This can happen reading/writing a key, or in your case when the node is bootstrapping and
trying to work out which endpoints are responsible for the token ranges. AFAIK adding the
migrations if an online process, the server is up and running while they are been added. So
if there is anything that happens while the schema is invalid that requires a valid schema
you will get the error. 

All the "Previous version mismatch. cannot apply." errors in the log for 0.4 mean it got a
migration from someone but the migration was received out of order. The current version on
the node is not the version that was present when this migration was applied. 
 
The simple answer is stop doing do what you're doing, it sounds dangerous and inefficient
to me. AFAIK it's not what the schema migrations were designed to do and moving from CL 1
to 3 will increase the repair workload.Aside from the risks of changing RF up and down a lot.
 

The long answer may be to always apply the schema changes on the same node; check there is
a single version of the schema before adding a new one; and take a look at monkeying around
with the Schema and Migrations CF's in the System KS to delete migrations you want skipped.


Am frowning and tutting and stoking my beard. 

Cheers

-----------------
Aaron Morton
Freelance Cassandra Developer
@aaronmorton
http://www.thelastpickle.com

On 2 Jul 2011, at 12:58, Jeremy Stribling wrote:

> Oops, forgot to mention that we're using Cassandra 0.7.2.
> 
> On 07/01/2011 05:46 PM, Jeremy Stribling wrote:
>> Hi all,
>> 
>> I'm running into a problem with Cassandra, where a new node coming up seems to only
get an incomplete set of schema mutations when bootstrapping, and as a result hits an "IllegalStateException:
replication factor (3) exceeds number of endpoints (2)" error.
>> 
>> I will describe the sequence of events below as I see them, but first I need to warn
you that I run Cassandra in a very non-standard way.  I embed it in a JVM, along with Zookeeper,
and other classes for a product we are working on.  We need to bring nodes up and down dynamically
in our product, including going from one node to three nodes, and back down to one, at any
time.  If we ever drop below three nodes, we have code that sets the replication factor of
our keyspaces to 1; similarly, whenever we have three or more nodes, we change the replication
factor to 3.  I know this is frowned upon by the community, but we're stuck with doing it
this way for now.
>> 
>> Ok, here's the scenario:
>> 
>> 1) Node 50.0.0.4 bootstraps into a cluster consisting of nodes 50.0.0.2 and 50.0.0.3.
>> 2) Once 50.0.0.4 is fully bootstrapped, we change the replication factor for our
two keyspaces to 3.
>> 3) Then node 50.0.0.2 is taken down permanently, and we change the replication factor
back down to 1.
>> 4) We then remove node 50.0.0.2's tokens using the removeToken call on node 50.0.0.3.
>> 5) Then we start node 50.0.0.5, and have it join the cluster using 50.0.0.3 and 50.0.0.4
as seeds.
>> 6) 50.0.0.5 starts receiving schema mutations to get it up to speed; the last one
it receives (7d51e757-a40b-11e0-a98d-65ed1eced995) has the replication factor at 3.  However,
there should be more schema updates after this that never arrive (you can see them arrive
at 50.0.0.4 while it is bootstrapping).
>> 7) Minutes after receiving this last mutation, node 50.0.0.5 hits the IllegalStateException
I've listed above, and I think for that reason never successfully joins the cluster.
>> 
>> My question is why doesn't node 50.0.0.5 receive the schema updates that follow 7d51e757-a40b-11e0-a98d-65ed1eced995?
 (For example, 8fc8820d-a40c-11e0-9eaf-6720e49624c2 is present in 50.0.0.4's log and sets
the replication factor back down to 1.)
>> 
>> I've put logs for nodes 50.0.0.3/4/5 at http://pdos.csail.mit.edu/~strib/cassandra_logs.tgz
.  The logs are pretty messy because they includes log messages from both Zookeeper and our
product code -- sorry about that.  Also, I think the clock on node 50.0.0.4 is a few minutes
ahead of the other nodes' clocks.
>> 
>> I also noticed in 50.0.0.4's log the following exceptions:
>> 
>> 2011-07-01 18:00:49,832 76315 [HintedHandoff:1] ERROR org.apache.cassandra.concurrent.DebuggableThreadPoolExecutor
 - Error in ThreadPoolExecutor
>> java.lang.RuntimeException: java.lang.RuntimeException: Could not reach schema agreement
with /50.0.0.3 in 60000ms
>>        at org.apache.cassandra.utils.WrappedRunnable.run(WrappedRunnable.java:34)
>>        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)

>>        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)

>>        at java.lang.Thread.run(Thread.java:662)
>> 
>> I don't know if that's related or not.
>> 
>> Thanks in advance,
>> 
>> Jeremy
>> 


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