Don’t Forget to Set the SEQUENCE CACHE Size

In most cases, simply creating an Oracle SEQUENCE with all defaults is good enough:

CREATE SEQUENCE my_sequence;

This sequence can then be used immediately in triggers when inserting new records in a table:

CREATE OR REPLACE TRIGGER my_trigger
  BEFORE INSERT 
  ON my_table
  FOR EACH ROW
  -- Optionally restrict this trigger to 
  -- fire only when really needed
  WHEN (new.id is null)
BEGIN
  SELECT my_sequence.nextval 
  INTO   :new.id
  FROM   DUAL;
END my_trigger;

But if your table has heavy throughput with millions of insertions per day (e.g. a log table), you better configure the sequence cache correctly. The Oracle manuals state

Note: Oracle recommends using the CACHE setting to enhance performance if you are using sequences in an Oracle Real Application Clusters environment.

We say: Consider using it also in other situations. Why? Sequence values are generated in an autonomous transaction. By default, Oracle caches 20 values before generating new ones in a new transaction. When you have a lot of inserts and thus generate a lot of sequence values, that will result in a lot of I/O on the sequence. Your best technique would be to run benchmarks to find a good value for your sequence cache in high-throughput scenarios.