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New MOXI error

4 replies [Last post]
Thu, 08/18/2011 - 15:55
ashleym1972
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Joined: 08/18/2011
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SERVER_ERROR proxy out of downstreams

What does this mean?

I have Moxi in a stand alone configuration using vbuckets to talk to a cluster of memcached servers. I think my cluster configuration is hosed since I'm not using membase and there are very few configuration examples that do not reference a membase configuration server. Here's my moxi-cluster.cfg

11211 = {
"hashAlgorithm": "CRC",
"numReplicas": 0,
"nodeLocator": "vbucket",
"serverList": [
"memcache101.fe:11211",
"memcache102.fe:11211",
"memcache103.fe:11211",
"memcache104.fe:11211",
"memcache105.fe:11211",
"memcache106.fe:11211",
"memcache107.fe:11211",
"memcache108.fe:11211",
"memcache109.fe:11211",
"memcache110.fe:11211",
"memcache111.fe:11211",
"memcache112.fe:11211",
"memcache113.fe:11211",
"memcache114.fe:11211",
"memcache115.fe:11211"
],
"vBucketMap": [
[0],[1],[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],
[0],[1],[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14]
]
}

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Thu, 08/25/2011 - 11:31
perry
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vbuckets are not compatible with standard memcached servers. I believe you'll need to change your "nodeLocator" to "ketama" and remove the vbucketmap.

I've asked one of our Moxi engineers to jump in and help as well...

Perry

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Thu, 08/25/2011 - 11:45
ashleym1972
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That's untrue. My error was using the wrong number of vBuckets (which must be a power of two). However, how could I know that since MOXI does not log the actual error from libvbucket. I submitted a pull request to fix this bug.

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Thu, 08/25/2011 - 12:13
perry
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Thanks Ashley, that sounds pretty accurate as well.

However, I would caution here that the standard memcached server implementation does not have any concept of vbuckets and so I really can't comment on how well this will work. Have you made changes outside of the standard offering?

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Thu, 08/25/2011 - 12:18
ashleym1972
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The standard memcached server cannot move data around and so does not support data replication, and thereby the full vbucket specification. However, the vbucket protocol is useful in the case of changing the number of servers in the cluster without totally getting f'ed by consistent hashing. Especially when you have a very sctive cluster with large amounts of data. Which is our case.

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