oracle tsn文件,Oracle datafile block 格式说明

最新推荐文章于 2024-04-23 15:53:31 发布

邓炯源

最新推荐文章于 2024-04-23 15:53:31 发布

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文章标签： oracle tsn文件

Oracle SCN（System Change Number）在数据库中用于跟踪更改。如果在同一个SCN下对同一块进行超过254行的修改，Oracle会分配新的SCN。当删除操作导致影响的行数超过254行时，可能会触发0xff标志，指示块损坏，引发ora-01578错误。损坏可能是由恢复过程中的NOLOGGING操作、软件bug或其他原因导致。

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seq:A sequence number incremented for each change to a block at the same SCN

A new SCN is allocated if the sequence number wraps.

同一个SCN影响这个block中的行数大于 254 行就会为这个事务分配一个新的SCN

如下面的操作就可能引起同一个SCN但影响的同一个block 中的行超过254行

"delete from table_name"

影响的行数(最大254) 是用从 0x01 到 0xfe 表示的

当这个byte 的数据为 0xff 的时候标志这个 block 坏调了---> ora-01578

Sequence number:

SEQ -> 0 /* non-logged changes - do not advance seq# */

SEQ -> (UB1MAXVAL-1)/* maximum possible sequence number */

SEQ -> (UB1MAXVAL) /* seq# to indicate a block is corrupt,equal to FF. soft corrupt*/

0xff : When present it indicates that the block has been marked as corrupt by Oracle. either by the db_block_checking functionality or the equivalent events (10210 for data blocks, 10211 for index blocks, and 10212 for cluster blocks) when making a database change, or by the DBMS_REPAIR.FIX_CORRUPT_BLOCKS procedure, or by PMON after an unsuccessful online block recovery attempt while recovering a failed process, or by RMAN during a BACKUP, COPY or VALIDATE command with the CHECK LOGICAL option. Logical corruptions are normally due to either recovery through a NOLOGGING operation, or an Oracle software bug.