Database / Google Spanner Database Interview questions
How do you apply schema changes in Spanner?
Schema changes are applied as DDL statements, such as ALTER TABLE, CREATE INDEX, or ADD COLUMN, submitted through the console, gcloud, or a client library's updateDatabaseDdl call.
ALTER TABLE Orders ADD COLUMN Status STRING(20);
Most DDL statements in Spanner run online: reads and writes continue against the table while the change propagates across replicas, and Spanner internally manages backfilling data for changes like adding a NOT NULL column with a default. Some operations, such as adding a column with a non-null default on a very large table, take longer because Spanner must backfill every existing row. Best practice is to batch related DDL statements together and monitor long-running operations before assuming they've completed.
Do most Spanner DDL changes require taking the database offline?
Why can adding a NOT NULL column with a default take longer on a large table?
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