> 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?
It just marks it to use that index if/when it is clustered, it doesn't do the clustering.
It's always kinda annoyed me that the CLUSTER command in Postgres doesn't work like it does on Microsoft SQL. In MSSQL, things will stay clustered as more data is inserted. In PG, you'd have to keep running CLUSTER as some sort of maintenance task every so often, so it's more of a one time command..
