RE: [EXTERNAL] Re: Cassandra 3.11.4 Node the load starts to increase after few minutes to 40 on 4 CPU machine

["Durity, Sean R" <SE...@homedepot.com>]

There is definitely a resource risk to having thousands of open connections to each node. Some of the drivers have (had?) less than optimal default settings, like acquiring 50 connections per Cassandra node. This is usually overkill. I think 5-10/node is much more reasonable. It depends on your app architecture and cluster node count. If there are lots of small micro-services, maybe they only need 2 connections per node.


Sean Durity – Staff Systems Engineer, Cassandra

From: Sergio <la...@gmail.com>
Sent: Wednesday, October 30, 2019 5:39 PM
To: user@cassandra.apache.org
Subject: [EXTERNAL] Re: Cassandra 3.11.4 Node the load starts to increase after few minutes to 40 on 4 CPU machine

Hi Reid,

I don't have anymore this loading problem.
I solved by changing the Cassandra Driver Configuration.
Now my cluster is pretty stable and I don't have machines with crazy CPU Load.
The only thing not urgent but I need to investigate is the number of ESTABLISHED TCP connections. I see just one node having 7K TCP connections ESTABLISHED while the others are having around 4-6K connection opened. So the newest nodes added into the cluster have a higher number of ESTABLISHED TCP connections.

default['cassandra']['sysctl'] = {
'net.ipv4.tcp_keepalive_time' => 60,
'net.ipv4.tcp_keepalive_probes' => 3,
'net.ipv4.tcp_keepalive_intvl' => 10,
'net.core.rmem_max' => 16777216,
'net.core.wmem_max' => 16777216,
'net.core.rmem_default' => 16777216,
'net.core.wmem_default' => 16777216,
'net.core.optmem_max' => 40960,
'net.ipv4.tcp_rmem' => '4096 87380 16777216',
'net.ipv4.tcp_wmem' => '4096 65536 16777216',
'net.ipv4.ip_local_port_range' => '10000 65535',
'net.ipv4.tcp_window_scaling' => 1,
  'net.core.netdev_max_backlog' => 2500,
  'net.core.somaxconn' => 65000,
'vm.max_map_count' => 1048575,
'vm.swappiness' => 0
}

These are my tweaked value and I used the values recommended from datastax.

Do you have something different?

Best,
Sergio

Il giorno mer 30 ott 2019 alle ore 13:27 Reid Pinchback <rp...@tripadvisor.com>> ha scritto:
Oh nvm, didn't see the later msg about just posting what your fix was.

R


On 10/30/19, 4:24 PM, "Reid Pinchback" <rp...@tripadvisor.com>> wrote:

     Message from External Sender

    Hi Sergio,

    Assuming nobody is actually mounting a SYN flood attack, then this sounds like you're either being hammered with connection requests in very short periods of time, or your TCP backlog tuning is off.   At least, that's where I'd start looking.  If you take that log message and google it (Possible SYN flooding... Sending cookies") you'll find explanations.  Or just googling "TCP backlog tuning".

    R


    On 10/30/19, 3:29 PM, "Sergio Bilello" <la...@gmail.com>> wrote:

        >
        >Oct 17 00:23:03 prod-personalization-live-data-cassandra-08 kernel: TCP: request_sock_TCP: Possible SYN flooding on port 9042. Sending cookies. Check SNMP counters.




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