Re: Recovery tools

Hannu Krosing wrote:

>Tom Lane kirjutas E, 14.04.2003 kell 17:26:
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>>mlw <pgsql@mohawksoft.com> writes:
>>    
>>
>>>Just suppose that all the log files are gone, and the only thing left is 
>>>some of the files in the /data directory. Is there any way to scan this 
>>>data and dump it to a file which could subsequently be used with a "COPY 
>>>FROM STDIN" on a new database?
>>>      
>>>
>>There aren't separate tools, and I'm not sure there could or should be.
>>What I'd do in that situation is:
>>    * pg_resetxlog to get a minimally valid xlog
>>    * if clog is missing, gin up files containing 0x55 everywhere
>>      (to make it look like every transaction has committed --- or
>>      put 00 everywhere if you'd rather assume that recent
>>      transactions all aborted)
>>    * start postmaster, look around, fix problems until I can pg_dump.
>>
>>AFAICS, you can make tools that work at the page/item level (like
>>pg_filedump, see http://sources.redhat.com/rhdb/), but there is hardly
>>any scope for doing anything intermediate between that and a full
>>postmaster.  There's no hope of decoding the contents of a tuple without
>>access to the table's tuple descriptor, which means you need most of the
>>system catalog mechanisms; plus you'd need the I/O routines for the
>>datatypes involved.  Might as well just use the postmaster as your data
>>inspection tool.
>>    
>>
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>I have a small python script that does dump at page/tuple level and lets
>people write their own tuple decoding routines. 
>
>This could probably be used here too, as usually the original scripts
>that created the database can be found and the tuples internal structure
>is not too complicated.
>
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So, what if, we added a PostgreSQL routine that dumps the tuple layout 
when a table is created, and put it in a directory like: 
/data/layout/db/ffff.ext automatically.

Then we include a version of your program which can read the layout and 
dump a table. That would answer Tom's issues. It would certainly be an 
important "when all else fails" tool that may save your ass.

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