If you are facing storage corruption or some other storage-related problem that might be related to bad blocks in a table, the pageinspect extension might be the module you are looking for:
test=# CREATE EXTENSION pageinspect;CREATE EXTENSION
The idea behind pageinspect is to provide you with a module that allows you to inspect a table on the binary level.
When using the module, the most important thing to do is to fetch a block:
test=# SELECT * FROM get_raw_page('pg_class', 0);...
The function will return a single block. In the preceding example, it is the first block in the pg_class parameter, which is a system table (of course, you can use any other table you want).
In the next step, you can extract ...
