how critical is WAL

Hi,

I happenned to come across the following in the
documentation on WAL implementation in v7.1 -

*****************************************************
Before WAL, any crash during writing could result in:

1.index tuples pointing to non-existent table rows

2.index tuples lost in split operations

3.totally corrupted table or index page content,
because of partially written data pages
*****************************************************

Does anybody know what kind of a problem this refers
to ? Does this mean that incomplete transactions would
be stored or does this mean that the entire table
might get corrupted and unusable, implying loss of all
data ?

( I am using postgresql v7.0.x , and would ideally
like to migrate to v7.1 after a few months ... unless
it is critical enough to do so earlier. )

Thanks,
Rini

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