When does CLUSTER occur?

Hi,

I’m looking for some general info on the behavior of CLUSTER.  I add large amounts of data to an existing table something like this:

BEGIN;

DROP INDEX IF EXISTS xgen1011_si_sn;

COMMIT;

BEGIN;

INSERT INTO gen1011

[snip]

COMMIT;

BEGIN;

CREATE INDEX xgen1011_si_sn

  ON gen1011

  USING btree

  (sample_id, snp_number)

  WITH (FILLFACTOR=100)

TABLESPACE index_tablespace;

ALTER TABLE gen1011 CLUSTER ON xgen1011_si_sn;

COMMIT;

My question is whether or not the “ALTER TABLE gen1011 CLUSTER ON xgen1011_si_sn” actually clusters the table at that point or if it just tells it to use that index for clustering?  If the latter I assume I need to add a “CLUSTER gen1011 ON xgen1011_si_sn” line at the end along with an ANALYSE line?

Thanks,

Bob