x$bh详解(一)

X$BH Fixed Table Buffer Cache Diagram 

Column Type Description
~~~~~~ ~~~~~ ~~~~~~~~~~~
ADDR RAW(4) Hex address of the Buffer Header.
INDX NUMBER Buffer Header number
BUF# NUMBER
HLADDR RAW(4) Hash Chain Latch Address
See . ADDR

LRU_FLAG NUMBER 8.1+ LRU flag
KCBBHLDF 0x01 8.1 LRU Dump Flag used in debug print routine
KCBBHLMT 0x02 8.1 moved to tail of lru (for extended stats) 
KCBBHLAL 0x04 8.1 on auxiliary list 
KCBBHLHB 0x08 8.1 hot buffer - not in cold portion of lru 

FLAG NUMBER 
KCBBHFBD 0x00001 buffer dirty 
KCBBHFAM 0x00002 7.3 about to modify; try not to start io 
KCBBHFAM 0x00002 8.0 about to modify; try not to start io 
KCBBHNAC 0x00002 8.1 notify dbwr after change 
KCBBHFMS 0x00004 modification started, no new writes
KCBBHFBL 0x00008 block logged 
KCBBHFTD 0x00010 temporary data - no redo for changes 
KCBBHFBW 0x00020 being written; can't modify 
KCBBHFWW 0x00040 waiting for write to finish
KCBBHFCK 0x00080 7.3 checkpoint asap 
0x00080 8.0 not used
KCBBHFMW 0x00080 8.1 multiple waiters when gc lock acquired
KCBBHFRR 0x00100 recovery reading, do not reuse, being read 
KCBBHFUL 0x00200 unlink from lock element - make non-current
KCBBHFDG 0x00400 write block & stop using for lock down grade
KCBBHFCW 0x00800 write block for cross instance call
KCBBHFCR 0x01000 reading from disk into KCBBHCR buffer
KCBBHFGC 0x02000 has been gotten in current mode
KCBBHFST 0x04000 stale - unused CR buf made from current
0x08000 7.3 Not used.
KCBBHFDP 0x08000 8.0 deferred ping
KCBBHFDP 0x08000 8.1 deferred ping
KCBBHFDA 0x10000 Direct Access to buffer contents
KCBBHFHD 0x20000 Hash chain Dump used in debug print routine






KCBBHFIR 0x40000 Ignore Redo for instance recovery 
KCBBHFSQ 0x80000 sequential scan only flag
KCBBHFNW 0x100000 7.3 Set to indicate a buffer that is NEW
0x100000 8.0 Not used
KCBBHFBP 0x100000 8.1 Indicates that buffer was prefetched 
KCBBHFRW 0x200000 7.3 re-write if being written (sort) 
0x200000 8.0 Not used
KCBBHFFW 0x200000 8.1 Buffer has been written once
KCBBHFFB 0x400000 buffer is "logically" flushed 
KCBBHFRS 0x800000 ReSilvered already - do not redirty 
KCBBHFKW 0x1000000 7.3 ckpt writing flag to avoid rescan */
0x1000000 8.0 Not used
KCBBHDRC 0x1000000 8.1 buffer is nocache 
0x2000000 7.3 Not used
KCBBHFRG 0x2000000 8.0 Redo Generated since block read 
KCBBHFRG 0x2000000 8.1 Redo Generated since block read 
KCBBHFWS 0x10000000 8.0 Skipped write for checkpoint. 
KCBBHFDB 0x20000000 8.1 buffer is directly from a foreign DB 
KCBBHFAW 0x40000000 8.0 Flush after writing 
KCBBHFAW 0x40000000 8.1 Flush after writing 

TS# NUMBER 8.X Tablespace number
DBARFIL NUMBER 8.X Relative file number of block
DBAFIL NUMBER 7.3 File number of block
DBABLK NUMBER Block number of block
CLASS NUMBER See Note 33434.1

STATE NUMBER 
KCBBHFREE 0 buffer free 
KCBBHEXLCUR 1 buffer current (and if DFS locked X) 
KCBBHSHRCUR 2 buffer current (and if DFS locked S)
KCBBHCR 3 buffer consistant read 
KCBBHREADING 4 Being read 
KCBBHMRECOVERY 5 media recovery (current & special) 
KCBBHIRECOVERY 6 Instance recovery (somewhat special)

MODE_HELD NUMBER Mode buffer held in (MODE pre 7.3)
0=KCBMNULL, KCBMSHARE, KCBMEXCL

CHANGES NUMBER
CSTATE NUMBER
X_TO_NULL NUMBER Count of PINGS out (OPS)
DIRTY_QUEUE NUMBER You wont normally see buffers on the LRUW
LE_ADDR RAW(4) Lock Element address (OPS)
SET_DS RAW(4) Buffer cache set this buffe