gpadmin=# \d gp_fastsequence

Table "pg_catalog.gp_fastsequence"

Column | Type | Modifiers
---------------+--------+-----------
objid | oid | not null
objmod | bigint | not null
last_sequence | bigint | not null

Indexes:
"gp_fastsequence_objid_objmod_index" UNIQUE, btree (objid, objmod)

The gp_fastsequence table contains information about indexes on append-optimized column-oriented tables. It is used to track the maximum row number used by a file segment of an append-optimized column-oriented table.