SCN in blocks and datafile headers

Question

When CKPT updates datafiles headers with the new SCN is it also updates the datafiles blocks with the new SCN ?
Thank you,
Micheal.

Answer 1

imran khan wrote:
The SCN are not stored the datafile blocks in fact it stores the SCNs in terms of bitmaps..Cheers!An absolutely wrong statement! How you think that the transaction within a block would come to know that its committed or not if there is no SCN stored in the block?
See below the dump of a block and also the SCN info recorded in it,
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> select header_file, header_block from dba_segments where segment_name='EMP'
  2  ;
HEADER_FILE HEADER_BLOCK
          4          234
SQL> select blocks from dba_segments where segment_name='EMP' and owner='SCOTT';
    BLOCKS
         8
SQL> alter session set tracefile_identifier=myblockd;
Session altered.
SQL> alter system dump datafile 4 block 235;
System altered.
SQL> exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Windows XP Version V5.1 Service Pack 2
CPU                 : 2 - type 586
Process Affinity    : 0x0x00000000
Memory (Avail/Total): Ph:437M/2045M, Ph+PgF:1335M/3428M, VA:1663M/2047M
Instance name: orcl
Redo thread mounted by this instance: 1
Oracle process number: 30
Windows thread id: 4596, image: ORACLE.EXE (SHAD)
*** 2011-08-21 17:40:49.781
*** SESSION ID:(16.6) 2011-08-21 17:40:49.781
*** CLIENT ID:() 2011-08-21 17:40:49.781
*** SERVICE NAME:(SYS$USERS) 2011-08-21 17:40:49.781
*** MODULE NAME:(sqlplus.exe) 2011-08-21 17:40:49.781
*** ACTION NAME:() 2011-08-21 17:40:49.781
Start dump data blocks tsn: 4 file#:4 minblk 235 maxblk 235
Block dump from cache:
Dump of buffer cache at level 4 for tsn=4, rdba=16777451
Block dump from disk:
buffer tsn: 4 rdba: 0x010000eb (4/235)
scn: 0x0000.002c106e seq: 0x05 flg: 0x04 tail: 0x106e0605
frmt: 0x02 chkval: 0xed5f type: 0x06=trans data
Hex dump of block: st=0, typ_found=1There is for sure, a block level SCN that oracle maintains .
Aman....