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Cassandra Check Schema Agreement

by admin on September 14th, 2021

If a node is currently bootstrapping, we use a number of latches (org.apache.cassandra.service.MigrationTask#inflightTasks) to follow the requirements of the in-Flight scheme, and we do not continue with bootstrapping/stream until all the latches are released (or we wait for each). One of the problems is that if we have a large schema or if the schema consultation of the other nodes was slower than expected, we do not have an explicit check to ensure that we actually received a schema before continuing. Schema changes must be passed to all nodes in the cluster. Once they agree on a common version, let`s say they agree. In the following example, a node, 172.17.0.3, has a different schema from the other two nodes. As a temporary state, it does not matter, but if this state is maintained, it fails in the operations of the CQL. The test is implemented by repeatedly querying the system tables according to the schema version reported by each node until they all converge to the same value. If this does not happen within a set period of time, the driver abandons the wait. The standard timeout is 10 seconds, it can be customized when creating your cluster: establish a connection to one of the nodes in the second list of schemas. In this example, you can select the node “10.111.22.102”. Then we tried to link with CQLSH with each node in the cluster, but we always had the same problem. On each node, Cassandra was aware of the table and we could see the definition of the schema for the table, but if we followed it, we would have the following error: In the same way, here is the schema of the reservation key: while it is possible to increase “migration_task_wait_in_seconds”, To force the node to wait longer each latche, there are cases where it doesn`t help because the callbacks for the request_timeout_in_ms requirements of request_timeout_in_ms (10 seconds by default) of the mail service (org.apache.cassandra.net.net.messagingServices) expired before the other nodes could respond to the new node. To investigate schema disagreements, try running nodetool describecluster: We found a StackOverlow article that suggested that one solution for the schema mismatch problem was to pass the nodes one after the other.

We tried and it worked. Here are the steps that worked for us. If everything went well, you should see that the node “10.111.22.102” has been moved to the other list of schemas (note: the list of nodes is not sorted by IP): you can check your cluster with nodetool describecluster, which gives you output on each version of the node. I think you will see one or a few knots of the majority. Here is an example of one of my clusters (without any errors in schematic versions): after registration, the list is notified of all schema changes detected by the driver, no matter where they came from. When executing schematic movements, it is necessary to wait for the cluster to transmit the schema on all nodes. The schema agreement is implemented on the basis of this fix and made available through the abstract migration class. To execute a statement with a schema agreement, you can use the executeWithSchemaAgreement method. After executing a statement, you can check if the schema agreement has been concluded or if there has been a period of time: this patch verifies the verification of the schema implementation between the boot node and the rest of the live nodes before continuing the boot trapping. It also adds a trial to prevent the new node from flooding existing nodes with simultaneous pull-schema requirements, as can happen in large clusters of use…

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