About Dirty Buffer

In fact, we may have been v$bh this view is not enough.

Let's take a look at this view primary field description:


STATUS

VARCHAR2 (1)

Status of the buffer:
Free-not currently in the xcur-exclusive scur-shared current cr-consistent read read-being read from disk Mrec- In media recovery mode irec-in instance recovery mode?


DIRTY

VARCHAR2 (1)

Y-block modified

TEMP

VARCHAR2 (1)

Y-temporary Block

Ping

VARCHAR2 (1)

Y-block pinged

Stale

VARCHAR2 (1)

Y-block is stale

DIRECT

VARCHAR2 (1)

Y-direct Block


?

We noticed that V$dirty represents block modified.

?

If we trace further down:

Sql> Select View_definition from v$fixed_view_definition where view_name = ' gv$bh ';

View_definition
--------------------------------------------------------------------------------
Select bh.inst_id, file#, Dbablk, class, Decode (state,0, ' free ', 1, ' Xcur ', 2, ' scur ')
, 3, ' Cr ', 4, ' read ', 5, ' Mrec ', 6, ' Irec ', 7, ' write ', 8, ' pi '), X_to_null, Forced_reads,
Forced_writes, Bh.le_addr, Name,le_class, Decode (Bitand (flag,1), 0, ' N ', ' Y '), D
Ecode (Bitand (flag,16), 0, ' n ', ' Y '), Decode (Bitand (flag,1536), 0, ' n ', ' y '), Dec
Ode (Bitand (flag,16384), 0, ' n ', ' Y '), Decode (Bitand (flag,65536), 0, ' n ', ' y '), '
N ', obj, ts# from x$bh BH, x$le le where bh.le_addr = le.le_addr (+)


We can see the v$bh of the bottom of the show x$bh

Where the Dirty/temp/ping/stale/direct five fields in V$BH are derived from flag fields in X$BH

Format the output:

SELECT bh.inst_id, file#, Dbablk, CLASS,
?????? DECODE (state,
?????????????? 0, ' free ',
?????????????? 1, ' Xcur ',
?????????????? 2, ' Scur ',
?????????????? 3, ' CR ',
?????????????? 4, ' read ',
?????????????? 5, ' Mrec ',
?????????????? 6, ' Irec ',
?????????????? 7, ' write ',
?????????????? 8, ' pi '
????????????? ),
?????? X_to_null, Forced_reads, Forced_writes, Bh.le_addr, NAME, Le_class,
?????? DECODE (Bitand (flag, 1), 0, ' N ', ' Y '),
?????? DECODE (Bitand (flag), 0, ' N ', ' Y '),
?????? DECODE (Bitand (flag, 1536), 0, ' N ', ' Y '),
?????? DECODE (Bitand (flag, 16384), 0, ' N ', ' Y '),
?????? DECODE (Bitand (flag, 65536), 0, ' n ', ' Y '), ' n ', obj, ts#
? From X$bh BH, x$le le
? WHERE bh.le_addr = le.le_addr (+)


Thus we can peep into the deep meaning of x$bh.flag.