I'm wondering if your table or particularly a heap file having a clustered index produced on among the characteristics is sorted on that attribute.It is possible to distinction between a sorted heap file along with a heap file with clustered index ?
It is possible to distinction between a sorted heap file along with a heap file with clustered index ?
Sorted heap file is really a heap (array-like structure) using the elements purchased. This is exactly what
MyISAM does with
ALTER TABLE … ORDER BY … or
PostgreSQL does with
CLUSTER. Placing a brand new record into this type of table breaks an order.
Clustered index is really a
B-Tree. Placing a brand new record keeps an order.
The records inside a clustered table aren't always physically purchased (in this way the record having a greater worth of the clustering key includes a greater offset inside a file or tablespace).
Rather, the records are realistically purchased: you are able to traverse in one record to a different following
B-Tree links (or direct links between pages just in case of the
B+Tree), but this still suggests random disk seeks since the pages linked realistically don't always reside near one another around the disk.
Oracle for example, allow reading through the indexes in physical order (utilizing an operation referred to as
INDEX FAST FULL SCAN) which doesn't keep up with the logical order but is faster due to the advantages or consecutive accessibility pages.
There's no such factor like a "heap file having a clustered index": a table organization is either heap or clustered.