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Re: Hinted Handoff


Does Cassandra TTL out the hints after max_hint_window_in_ms? From my understanding, Cassandra only stops collecting hints after max_hint_window_in_ms but can still keep replaying the hints if the node comes back again. Is this correct? Is there a way to TTL out hints?

No, but it won't send hints that have passed HH window. Also, this shouldn't be caused by HH as the hints maintain the original timestamp with which they were written. 

Honestly, this sounds more like a use case for a distributed cache rather than Cassandra. Keeping data for 30 minutes and then deleting it is going to be a nightmare to manage in Cassandra.

On 7 August 2018 at 07:20, Agrawal, Pratik <paagrawa@xxxxxxxxxx.invalid> wrote:

Does Cassandra TTL out the hints after max_hint_window_in_ms? From my understanding, Cassandra only stops collecting hints after max_hint_window_in_ms but can still keep replaying the hints if the node comes back again. Is this correct? Is there a way to TTL out hints?

 

Thanks,

Pratik

 

From: Kyrylo Lebediev <Kyrylo_Lebediev@xxxxxxxx.INVALID>
Reply-To: "user@xxxxxxxxxxxxxxxxxxxx" <user@xxxxxxxxxxxxxxxxxxxx>
Date: Monday, August 6, 2018 at 4:10 PM
To: "user@xxxxxxxxxxxxxxxxxxxx" <user@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: Hinted Handoff

 

Small gc_grace_seconds value lowers max allowed node downtime, which is 15 minutes in your case. After 15 minutes of downtime you'll need to replace the node, as you described. This interval looks too short to be able to do planned maintenance. So, in case you set larger value for gc_grace_seconds (lets say, hours or a day) will you get visible read amplification / waste a lot of disk space / issues with compactions?

 

Hinted handoff may be the reason in case hinted handoff window is longer than gc_grace_seconds. To me it looks like hinted handoff window (max_hint_window_in_ms in cassandra.yaml, which defaults to 3h) must always be set to a value less than gc_grace_seconds.

 

Regards,

Kyrill


From: Agrawal, Pratik <paagrawa@xxxxxxxxxx.INVALID>
Sent: Monday, August 6, 2018 8:22:27 PM
To: user@xxxxxxxxxxxxxxxxxxxx
Subject: Hinted Handoff

 

Hello all,

We use Cassandra in non-conventional way, where our data is short termed (life cycle of about 20-30 minutes) where each record is updated ~5 times and then deleted. We have GC grace of 15 minutes.

We are seeing 2 problems

1.) A certain number of Cassandra nodes goes down and then we remove it from the cluster using Cassandra removenode command and replace the dead nodes with new nodes. While new nodes are joining in, we see more nodes down (which are not actually down) but we see following errors in the log

“Gossip not settled after 321 polls. Gossip Stage active/pending/completed: 1/816/0”

 

To fix the issue, I restarted the server and the nodes now appear to be up and the problem is solved

 

Can this problem be related to https://issues.apache.org/jira/browse/CASSANDRA-6590 ?

 

2.) Meanwhile, after restarting the nodes mentioned above, we see that some old deleted data is resurrected (because of short lifecycle of our data). My guess at the moment is that these data is resurrected due to hinted handoff. Interesting point to note here is that data keeps resurrecting at periodic intervals (like an hour) and then finally stops. Could this be caused by hinted handoff? if so is there any setting which we can set to specify that “invalidate, hinted handoff data after 5-10 minutes”.

 

Thanks,
Pratik




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