no easy answer (was Re: [PLUG] MySQL v. PostgreSQL -- perhaps an easy answer)

Felix Lee felix.1 at canids.net
Fri Jan 16 03:08:01 UTC 2004


> >    An alternative file-system backup approach is to make a
> >    "consistent snapshot" of the data directory, if the file
> >    system supports that functionality.  Such a snapshot will save
> >    the database files in a state where the database server was
> >    not properly shut down; therefore, when you start the database
> >    server on this backed up directory, it will think the server
> >    had crashed and replay the WAL log.  This is not a problem,
> >    just be aware of it.

this paragraph in the documentation was added in the postgres 7.4
release, without editing the rest of that page to be consistent
with that statement.  the CVS revision date is November 2003.  I
don't know why this would be special to 7.4.  it seems to me this
should be true for any release with WAL, except for bugs.

the release notes for 7.4 lists one WAL-related bug
    Make B-tree indexes fully WAL-safe (Tom)

    In prior releases, under certain rare cases, a server crash
    could cause B-tree indexes to become corrupt. This release
    removes those last few rare cases.

anyway, this is as far as I'm going to dig into this.  anyone who
cares will have to do more research themselves, heh.

(I don't have any reason to choose a database right now, and
there's not much value in finding more information until I do,
since technology is changing rapidly, and I suspect any
impressions I form now will be obsolete in a year.  this was
partly an exercise in information gathering, and also to get more
familiar with database issues.)
--




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