Re: Thanks, naming conventions, and count() - Mailing list pgsql-hackers

On Sun, 29 Apr 2001, Bruce Momjian wrote:

> > > Yes, I like that idea, but the problem is that it is hard to update just
> > > one table in the file.  You sort of have to update the entire file each
> > > time a table changes.  That is why I liked symlinks because they are
> > > per-table, but you are right that the symlink creation could fail
> > > because the new table file was never created or something, leaving the
> > > symlink pointing to nothing.  Not sure how to address this.  Is there a
> > > way to update a flat file when a single table changes?
> >
> > Why not just dump the whole file?  That way, if a previosu dump failed for
> > whatever reason, the new dump would correct that omission ...
>
> Yes, you can do that, but it is only updated during a dump, right?
> Makes it hard to use during the day, no?
>
> >
> > Then again, why not some sort of 'lsdb' command that looks at where it is
> > and gives you info as appropriate?
>
>
> I want to do that for oid2name.  I had the plan layed out, but never got
> to it.
>
> >
> > if in data/base, then do a connect to template1 using postgres so that you
> > can dump and parse the raw data from pg_database ... if in a directory,
> > you should be able to connect to that database in a similar way to grab
> > the contents of pg_class ...
> >
> > no server would need to be running for this to work, and if it was
> > readonly, it should be workable if a server is running, no?
>
> I think parsing the file contents is too hard.  The database would have
> to be running and I would use psql.

I don't know, I recovered someone's database using a "raw" connection ...
wasn't that difficult once I figured out the format *shrug*

the following gets the oid,relname's for a database in the format:

echo "select oid,relname from pg_class" | postgres -L -D /usr/local/pgsql/data eceb | egrep "oid|relname"

then just parse the output using a simple perl script:
        1: oid = "163338"      (typeid = 26, len = 4, typmod = -1, byval = t)        2: relname = "auth_info_uid_key"
   (typeid = 19, len = 32, typmod = -1, byval = f)        1: oid = "163341"      (typeid = 26, len = 4, typmod = -1,
byval= t)        2: relname = "auth_info_id"    (typeid = 19, len = 32, typmod = -1, byval = f)        1: oid = "56082"
     (typeid = 26, len = 4, typmod = -1, byval = t)        2: relname = "auth_info"       (typeid = 19, len = 32,
typmod= -1, byval = f)
 

the above won't work on a live database, did try that, so best is to test
for a connection first, and this would be a fall back ... but you'd at
least have a live *and* non live way of parsing the data *shrug*