Block Types

Every Oracle database block has a block type. The block type is stored in the first byte of the block. It is reported in the block dump (ALTER SYSTEM DUMP DATAFILE x BLOCK y)

The following table shows the known block types in Oracle 10.2.

TypeDescription
1KTU UNDO HEADER
2KTU UNDO BLOCK
3KTT SAVE UNDO HEADER
4KTT SAVE UNDO BLOCK
5DATA SEGMENT HEADER
6trans data
7Unknown
8Unknown
9Unknown
10DATA SEGMENT FREE LIST BLOCK
11Unknown
12DATA SEGMENT HEADER WITH FREE LIST BLOCKS
13Compatibility segment
14KTU UNDO HEADER W/UNLIMITED EXTENTS
15KTT SAVE UNDO HEADER W/UNLIMITED EXTENTS
16DATA SEGMENT HEADER - UNLIMITED
17DATA SEGMENT HEADER WITH FREE LIST BLKS - UNLIMITED
18EXTENT MAP BLOCK
19Unknown
20Unknown
21Unknown
22DATA SEGMENT FREE LIST BLOCK WITH FREE BLOCK COUNT
23BITMAPPED DATA SEGMENT HEADER
24BITMAPPED DATA SEGMENT FREELIST
25BITMAP INDEX BLOCK
26BITMAP BLOCK
27LOB BLOCK
28KTU BITMAP UNDO HEADER - LIMITED EXTENTS
29KTFB Bitmapped File Space Header
30KTFB Bitmapped File Space Bitmap
31TEMP INDEX BLOCK
32FIRST LEVEL BITMAP BLOCK
33SECOND LEVEL BITMAP BLOCK
34THIRD LEVEL BITMAP BLOCK
35PAGETABLE SEGMENT HEADER
36PAGETABLE EXTENT MAP BLOCK
37EXTENT MAP BLOCK OF SYSTEM MANAGED UNDO SEGMENT
38KTU SMU HEADER BLOCK
39Unknown
40PAGETABLE MANAGED LOB BLOCK
41Unknown
42Unknown
43Unknown
44Unknown
45Unknown
46Unknown
47Unknown

The above list is identical in Oracle 9.2

Note that all data and index blocks are of type trans data