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The `notifications.id` column is the most probable column to run out of values. This is because it is an `int` column that has only 2147483647 values and many notifications are generated on a regular basis in an active community. This commit migrates the column to `bigint`. These migrations do not use `ALTER TABLE ... COLUMN ... TYPE` in order to avoid the `ACCESS EXCLUSIVE` lock on the entire table. Instead, they create a new `bigint` column, copy the values to the new column and then sets the new column as primary key. Related columns (see `user_badges`, `shelved_notifications`) will be migrated in a follow-up commit.
39 lines
1.0 KiB
Ruby
39 lines
1.0 KiB
Ruby
# frozen_string_literal: true
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class AddBigIntNotificationsId < ActiveRecord::Migration[7.0]
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def up
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# Short-circuit if the table has been migrated already
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result =
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execute(
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"SELECT data_type FROM information_schema.columns WHERE table_name = 'notifications' AND column_name = 'id' LIMIT 1",
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)
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data_type = result[0]["data_type"]
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return if data_type.downcase == "bigint"
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# Create new column
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execute "ALTER TABLE notifications ADD COLUMN new_id BIGINT NOT NULL DEFAULT 0"
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# Mirror new `id` values to `new_id`
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execute <<~SQL.squish
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CREATE FUNCTION mirror_notifications_id()
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RETURNS trigger AS
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$$
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BEGIN
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NEW.new_id = NEW.id;
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RETURN NEW;
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END;
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$$
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LANGUAGE plpgsql
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SQL
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execute <<~SQL.squish
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CREATE TRIGGER notifications_new_id_trigger BEFORE INSERT ON notifications
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FOR EACH ROW EXECUTE PROCEDURE mirror_notifications_id()
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SQL
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end
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def down
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raise ActiveRecord::IrreversibleMigration
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end
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end
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