BREF (Unicode: 16 bytes; ANSI: 8 bytes): BREF structure (section ) that points to the child BTPAGE. BBTENTRY (Leaf BBT Entry) BBTENTRY records contain information blocks and are found in BTPAGES with cLevel equal to 0, with the ptype of "ptypeBBT". These are the leaf entries of the BBT. As noted in section , these structures MAY NOT be tightly packed and the cbEnt field of the BTPAGE SHOULD be used to iterate over the entries. Unicode: 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 BREF (16 bytes) ... ... cb cRef dwPadding ANSI: 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 BREF ... cb cRef structure (section ) that contains the BID and IB BREF (Unicode: 16 bytes; ANSI: 8 bytes): BREF of the block that the BBTENTRY references. cb (2 bytes): The count of bytes of the raw data contained in the block referenced by BREF excluding the block trailer and alignment padding, if any. cRef (2 bytes): Reference count indicating the count of references to this block. See section regarding how reference counts work. dwPadding (Unicode file format only, 4 bytes): Padding; MUST be set to zero. Reference Counts To improve storage efficiency, the NDB supports single-instancing by allowing multiple entities to reference the same data This is supported at the BBT level by having reference counts for blocks. For example, when a node is copied, a new node is created with a new NID, but instead of making a separate copy of the entire contents of the node, the new node simply references the existing immediate data and subnode blocks by incrementing the reference count of each block.
BREF (Unicode: 16 bytes; ANSI: 8 bytes): BREF structure (section ) that points to the child BTPAGE. BBTENTRY (Leaf BBT Entry) BBTENTRY records contain information blocks and are found in BTPAGES with cLevel equal to 0, with the ptype of "ptypeBBT". These are the leaf entries of the BBT. As noted in section , these structures MAY NOT be tightly packed and the cbEnt field of the BTPAGE SHOULD be used to iterate over the entries. Unicode: 0 1 2 3 4 5 6 7 8 9 1 0 1 2 3 4 5 6 7 8 9 2 0 1 2 3 4 5 6 7 8 9 3 0 1 BREF (16 bytes) ... ... cb cRef dwPadding ANSI: 0 1 2 3 4 5 6 7 8 9 1 0 1 2 3 4 5 6 7 8 9 2 0 1 2 3 4 5 6 7 8 9 3 0 1 BREF ... cb cRef BREF (Unicode: 16 bytes; ANSI: 8 bytes): BREF structure (section ) that contains the BID and IB of the block that the BBTENTRY references. cb (2 bytes): The count of bytes of the raw data contained in the block referenced by BREF excluding the block trailer and alignment padding, if any. cRef (2 bytes): Reference count indicating the count of references to this block. See section regarding how reference counts work. dwPadding (Unicode file format only, 4 bytes): Padding; MUST be set to zero. Reference Counts To improve storage efficiency, the NDB supports single-instancing by allowing multiple entities to reference the same data This is supported at the BBT level by having reference counts for blocks. For example, when a node is copied, a new node is created with a new NID, but instead of making a separate copy of the entire contents of the node, the new node simply references the existing immediate data and subnode blocks by incrementing the reference count of each block.