Cassandra: Add a cluster level lock to prevent any migration while the topology of the cluster is being modified about evolve HOT 6 CLOSED

so we don't even need a keyspace_to_lock column but only one

Yes correct. In this case to block schema change on the whole cluster, you need to use the consistency SERIAL instead of LOCAL_SERIAL for your LWT

from evolve.

Instead of creating/deleting the keyspace, you can just create a keyspace (ingenico_schema_change) and a table (lock) with the following schema:

CREATE TABLE lock(
   keyspace_to_lock text PRIMARY KEY
)

Before each topology change, do an INSERT with a TTL on this table (TTL value should be long enough to cover the duration of the topology change)

After the topology change, you issue an DELETE to remove the lock

from evolve.

@doanduyhai ok, got it, thanks. One last question: any replication factor or consistency level advice on this?

from evolve.

Standard replication factor of 3 should be fine.

For operations on lock/unlock since you're using LightWeightTransaction, the only choice of Consistency Level is LOCAL_SERIAL or SERIAL

LOCAL_SERIAL allows your lock operation to survive a crash of a whole datacenter.
SERIAL allows your lock operation to span across the cluster because it requires strict majority of replica on all data centers

from evolve.

Ok. Now, I was under the impression that this lock would be for the whole cluster - I guess what we want is to block any structural change in any keyspace in the cluster when the topology changes, so we don't even need a keyspace_to_lock column but only one.

In short, this table will contain a single record when a topology change is in progress (so no migration should occur) and no record when it is safe to migrate. Is that correct?

from evolve.

@Pvlerick Is this always an openned issue ?

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