How to load updated java class on a existing Ignite cluster?

I have a Ignite cluster of 2 or more nodes (max of 4) in server mode.

Let's say I have an Ignite cache defined by Java class called Employee (let's say this is version 1) loaded and used. If I update this Employee class with a new member field (version 2), how would I go about updating the loaded class with the new version (ie update the cache definition)? How does Ignite handle objects (cache records) created previously based on Employee version 1 vs new cache records created with Employee version 2? If I have SQL queries using new fields as defined in version 2, is that going to fail because the Employee version 1 based objects/cache records are not compatible with new SQL using the newly defined field(s) in Employee version 2?

I can delete db folder from the working directory, reload the new class as part of restarting the Ignite service. But, I lose all previous data.

Cluster member with updated Employee class definition will not join other nodes in the cluster still loaded with original Employee version 1 class. Again, I need to shutdown all members in the cluster and reload the new Employee version and restart all members in the cluster.

Ignite doesn't store code versions. The latest deployed class is in use.

in order to preserve the fields, Ignite builds binary meta for a customer type and stores it for validation. If you are going to add new fields and leave the old ones untouched, Ignite will update the meta automatically, nothing to configure/change. A old record will be deserialised with new fields set to null.

For SQL it's recommended to go with DDL to adjust the schema accordingly:

ALTER TABLE "schema".MyTable DROP COLUMN oldColumn
ALTER TABLE "schema".MyTable ADD COLUMN newColumn VARCHAR;

You can check available meta using control script --meta command (not sure if it's available in Ignite edition though)

control.sh --meta list

Ignite won't propagate POJO changes automatically using peerClassLoading. You should either update the JARs manually or rely on some deployment SPI, like URL deployment.

Overall, you should not remove your db folder each time you are going to make changes to your POJOs/SQL tables. Adding new fields should be totally OK. Do not remove the old fields, it's better to mark them as deprecated.