--一個改變向量描述了對一個獨立的數據塊的一個獨立的修改操作。這裏面我們要注意的是，
--對於CV的定義裏包含了兩層含義，一個CV只針對一個數據塊的變更，一個CV只包含一個變化。
--每個CV都包含了對文件的修改，因此在每個CV中都有一個OPCODE，指出修改的類型。不同OPCODE的CV，其組成是不同的，OPCODE的取值範圍包括：
Layer 1 : Transaction Control - KCOCOTCT
Opcode 1 : KTZFMT
Opcode 2 : KTZRDH
Opcode 3 : KTZARC
Opcode 4 : KTZREP
Layer 2 : Transaction Read - KCOCOTRD
Layer 3 : Transaction Update - KCOCOTUP
Layer 4 : Transaction Block - KCOCOTBK [ktbcts.h]
Opcode 1 : Block Cleanout
Opcode 2 : Physical Cleanout
Opcode 3 : Single Array Change
Opcode 4 : Multiple Changes to an Array
Opcode 5 : Format Block
Layer 5 : Transaction Undo - KCOCOTUN [ktucts.h]
Opcode 1 : Undo block or undo segment header - KTURDB
Opcode 2 : Update rollback segment header - KTURDH
Opcode 3 : Rollout a transaction begin
Opcode 4 : Commit transaction (transaction table update)
- no undo record
Opcode 5 : Create rollback segment (format) - no undo record
Opcode 6 : Rollback record index in an undo block - KTUIRB
Opcode 7 : Begin transaction (transaction table update)
Opcode 8 : Mark transaction as dead
Opcode 9 : Undo routine to rollback the extend of a rollback segment
Opcode 10 :Redo to perform the rollback of extend of rollback segment
to the segment header.
Opcode 11 :Rollback DBA in transaction table entry - KTUBRB
Opcode 12 :Change transaction state (in transaction table entry)
Opcode 13 :Convert rollback segment format (V6 -> V7)
Opcode 14 :Change extent allocation parameters in a rollback segment
Opcode 15 :
Opcode 16 :
Opcode 17 :
Opcode 18 :
Opcode 19 : Transaction start audit log record
Opcode 20 : Transaction continue audit log record
Opcode 24 : Kernel Transaction Undo Relog CHanGe - KTURLGU
Layer 6 : Control File - KCOCODCF [tbs.h]
Layer 10 : INDEX - KCOCODIX [kdi.h]
Opcode 1 : load index block (Loader with direct mode)
Opcode 2 : Insert leaf row
Opcode 3 : Purge leaf row
Opcode 4 : Mark leaf row deleted
Opcode 5 : Restore leaf row (clear leaf delete flags)
Opcode 6 : Lock index block
Opcode 7 : Unlock index block
Opcode 8 : Initialize new leaf block
Opcode 9 : Apply Itl Redo
Opcode 10 :Set leaf block next link
Opcode 11 :Set leaf block previous link
Opcode 12 :Init root block after split
Opcode 13 :Make leaf block empty
Opcode 14 :Restore block before image
Opcode 15 :Branch block row insert
Opcode 16 :Branch block row purge
Opcode 17 :Initialize new branch block
Opcode 18 :Update keydata in row
Opcode 19 :Clear row's split flag
Opcode 20 :Set row's split flag
Opcode 21 :General undo above the cache (undo)
Opcode 22 :Undo operation on leaf key above the cache (undo)
Opcode 23 :Restore block to b-tree
Opcode 24 :Shrink ITL (transaction entries)
Opcode 25 :Format root block redo
Opcode 26 :Undo of format root block (undo)
Opcode 27 :Redo for undo of format root block
Opcode 28 :Undo for migrating block
Opcode 29 :Redo for migrating block
Opcode 30 :IOT leaf block nonkey update
Opcode 31 :Cirect load root redo
Opcode 32 :Combine operation for insert and restore rows
Layer 11 : Row Access - KCOCODRW [kdocts.h]
Opcode 1 : Interpret Undo Record (Undo)
Opcode 2 : Insert Row Piece
Opcode 3 : Drop Row Piece
Opcode 4 : Lock Row Piece
Opcode 5 : Update Row Piece
Opcode 6 : Overwrite Row Piece
Opcode 7 : Manipulate First Column (add or delete the 1rst column)
Opcode 8 : Change Forwarding address
Opcode 9 : Change the Cluster Key Index
Opcode 10 :Set Key Links (change the forward & backward key links
on a cluster key)
Opcode 11 :Quick Multi-Insert (ex: insert as select ...)
Opcode 12 :Quick Multi-Delete
Opcode 13 :Toggle Block Header flags
Layer 12 : Cluster - KCOCODCL [?]
Layer 13 : Transaction Segment - KCOCOTSG [ktscts.h]
Opcode 1 : Data segment format
Opcode 2 : Merge
Opcode 3 : Set link in block
Opcode 4 : Not used
Opcode 5 : New block (affects segment header)
Opcode 6 : Format block (affects data block)
Opcode 7 : Record link
Opcode 8 : Undo free list (undo)
Opcode 9 : Redo free list head (called as part of undo)
Opcode 9 : Format free list block (freelist group)
Opcode 11 :Format new blocks in free list
Opcode 12 :free list clear
Opcode 13 :free list restore (back) (undo of opcode 12)
Layer 14 : Transaction Extent - KCOCOTEX [kte.h]
Opcode 1 : Add extent to segment
Opcode 2 : Unlock Segment Header
Opcode 3 : Extent DEaLlocation (DEL)
Opcode 4 : Undo to Add extent operation (see opcode 1)
Opcode 5 : Extent Incarnation number increment
Opcode 6 : Lock segment Header
Opcode 7 : Undo to rollback extent deallocation (see opcode 3)
Opcode 8 : Apply Position Update (truncate)
Opcode 9 : Link blocks to Freelist
Opcode 10 :Unlink blocks from Freelist
Opcode 11 :Undo to Apply Position Update (see opcode 8)
Opcode 12 :Convert segment header to 6.2.x type
Layer 15 : Table Space - KCOCOTTS [ktt.h]
Opcode 1 : Format deferred rollback segment header
Opcode 2 : Add deferred rollback record
Opcode 3 : Move to next block
Opcode 4 : Point to next deferred rollback record
Layer 16 : Row Cache - KCOCOQRC
Layer 17 : Recovery (REDO) - KCOCORCV [kcv.h]
Opcode 1 : End Hot Backup : This operation clears the hot backup
in-progress flags in the indicated list of files
Opcode 2 : Enable Thread : This operation creates a redo record
signalling that a thread has been enabled
Opcode 3 : Crash Recovery Marker
Opcode 4 : Resizeable datafiles
Opcode 5 : Tablespace ONline
Opcode 6 : Tablespace OFFline
Opcode 7 : Tablespace ReaD Write
Opcode 8 : Tablespace ReaD Only
Opcode 9 : ADDing datafiles to database
Opcode 10 : Tablespace DRoP
Opcode 11 : Tablespace PitR
Layer 18 : Hot Backup Log Blocks - KCOCOHLB [kcb.h]
Opcode 1 : Log block image
Opcode 2 : Recovery testing
Layer 19 : Direct Loader Log Blocks - KCOCODLB [kcbl.h]
Opcode 1 : Direct block logging
Opcode 2 : Invalidate range
Opcode 3 : Direct block relogging
Opcode 4 : Invalidate range relogging
Layer 20 : Compatibility Segment operations - KCOCOKCK [kck.h]
Opcode 1 : Format compatibility segment - KCKFCS
Opcode 2 : Update compatibility segment - KCKUCS
Layer 21 : LOB segment operations - KCOCOLFS [kdl2.h]
Opcode 1 : Write data into ILOB data block - KDLOPWRI
Layer 22 : Tablespace bitmapped file operations - KCOCOTBF [ktfb.h]
Opcode 1 : format space header - KTFBHFO
Opcode 2 : space header generic redo - KTFBHREDO
Opcode 3 : space header undo - KTFBHUNDO
Opcode 4 : space bitmap block format - KTFBBFO
Opcode 5 : bitmap block generic redo - KTFBBREDO
Layer 23 : write behind logging of blocks - KCOCOLWR [kcbb.h]
Opcode 1 : Dummy block written callback - KCBBLWR
Layer 24 : Logminer related (DDL or OBJV# redo) - KCOCOKRV [krv.h]
Opcode : common portion of the ddl - KRVDDL
Opcode : direct load redo - KRVDLR
Opcode : lob related info - KRVLOB
Opcode : misc info - KRVMISC
Opcode : user info - KRVUSER--舉個例子，一個REDO RECORD裏可能包含3個CV，第一個是對UNDO SEGMENT HEADER的修改，
--第二個是對UNDO SEGMENT的修改，第三個是對DATA BLOCK的修改。而一個事務可能包含N個REDO RECORD。
--當前臺進程要對某個數據塊進行修改的時候，
--首先要形成相關的CHANGE VECTOR，然後把多個CV組成REDO RECORD，把REDO RECORD寫入LOG BUFFER後，前臺進程可以將CV提交到相關的數據塊上。