/* Typedef for callback function for table_index_build_scan */
typedef void (*IndexBuildCallback) (Relation index,
ItemPointer tid,
Datum *values,
bool *isnull,
bool tupleIsAlive,
void *state);
When we build an index on an existed heap table, so pg will read the tuple one by one and give the tuple’s hepatid as this ItemPointer, is that right?