full text catalog rebuild vs full text index start full populaton

Question

I have a two step job running periodically in SQL Server 2012.

1. ALTER FULLTEXT CATALOG [CatalogName] REBUILD
2. ALTER FULLTEXT INDEX ON [tblname] START FULL POPULATION

I didn't get the purpose of second step because google says that on first step itself sql server recreates catalog and generates indexes.

I would appreciate if someone could help me in understanding what happens internally during the execution of above two steps.

Answer 1

ALTER FULLTEXT CATALOG [CatalogName] REBUILD 

Deletes catalog and creates new. If this catalog has many indexes this rebuild could take a long time.

ALTER FULLTEXT INDEX ON [tblname] START FULL POPULATION 

Rebuildes only indexes on one of the tables.

If You have few indexes in one catalog both steps are equal. But if size of Catalog is much bigger and consist of many indexes, the first step would take much more time to run.