Re: Recovery tools

Hannu Krosing wrote:

>Tom Lane kirjutas E, 14.04.2003 kell 17:26:
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>
>>mlw <pgsql(at)mohawksoft(dot)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.
>>
>>
>
>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.
>
>
>
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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