Database / Mnesia intermediate to advanced Interview questions

What is mnesia:change_config(extra_db_nodes, Nodes) used for?

This call tells the local Mnesia instance about additional nodes it should try to connect and merge schema information with — it's the mechanism behind both joining a brand-new node to an existing cluster and reconnecting a node that was started independently but should now become part of a shared database.

mnesia:change_config(extra_db_nodes, ['nodeb@host', 'nodec@host']).
%% -> {ok, ['nodeb@host', 'nodec@host']}

It returns which of the listed nodes it actually managed to connect and merge schema with — not every listed node is guaranteed to succeed, for instance if one is unreachable. This is typically run once during a node's startup sequence (often from an application's startup code or a release's boot script) rather than being called repeatedly during normal operation.

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What does change_config(extra_db_nodes, Nodes) return? Always {ok, Nodes} for every listed node, with no exceptions

✗ Not quite. Try again.

{ok, ConnectedNodes} - the subset it actually managed to connect and merge with

✓ Correct! Well done.

Nothing; it's a fire-and-forget call

✗ Not quite. Try again.

When is this call typically made? Repeatedly during every transaction

✗ Not quite. Try again.

Once, as part of a node's startup sequence to join the cluster

✓ Correct! Well done.

Only when creating a brand-new schema

✗ Not quite. Try again.

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Database / Mnesia intermediate to advanced Interview questions

What is mnesia:change_config(extra_db_nodes, Nodes) used for?

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