Data Block Dump

Data Block Dump
A data block dump shows detailed information of the contents of the block for the given datafile number and the block number. It shows you exactly how the data is stored internally. Depending on whether it is a table or index segment, the data block will list the contents of rows or index keys. The segment header block dump will list the extent map information. The undo header block dump will list the free extent pool in the undo segments. You may need to dump the contents of the data block when investigating block corruptions. In addition, complex recovery situations also warrant block dumps to check the SCN of the block.
dump出数据块的内容，里面的内容有可能不同，取决于是表段还是索引段，可能会dump出rows或是index keys。对于undo段头的块，我们可以列出free的extent pool。我们调查data block corruptions就可以通过dump数据块，在做复杂的recovery时也可以通过dump数据块来得知数据块的SCN号。
Syntax
The following methods dump the contents of the interested data blocks to the trace file in the UDUMP directory. Data block dumps contain the actual data stored in the blocks.
dump出来放在UDUMP路径下
 Note
If your database instance has the hidden parameter _TRACE_FILES_PUBLIC set to TRUE, please remember that the trace file data can be viewed by anyone with access to your database server machine. It will compromise data security and confidentiality.

alter system dump datafile <file#> block <block#>;--提供file#与block#

alter system dump datafile <file#> block min <min_block#> block max <max_block#>;--dump出邻居的块

想dump出一个segment内的数据块：

select file_id, block_id, blocksfrom   dba_extentswhere  segment_name = ‘TEST’;   FILE_ID   BLOCK_ID     BLOCKS---------- ---------- ----------         1      29081          8
REM ---- To dump the segment header blockalter system dump datafile 1 block 29081;REM ---- To dump the data block next to the segment headeralter system dump datafile 1 block 29082REM ---- To dump both the blocks at the same timealter system dump datafile 1 block min 29081 block max 29082;
oradebug不能用来dump出数据块