Oops! Randy Yates <yates@ieee.org> was seen spray-painting on a wall:
> I'm a complete newbie to postgres so please look the other way if
> these questions are really stupid.
>
> Is it legitimate to have one database per data file? For
> organizational and backup purposes, I'd like to keep the database
> files for each of several projects separate. This means, e.g., that
> postmaster must have multiple instances going simultaneously?
>
> I'm thinking the answer is NO because, for one, the TCPIP connection
> seems to be to ONE instance of postmaster which then sorts out which
> database objects are in its container.
>
> Am I close?
Not terribly.
For a given "cluster" (e.g. - an instance initialized using "initdb"),
you have a set of databases, each of which is indicated by a directory
under 'base/' in that cluster.
Within each database in the cluster, each table and index is indicated
by one (or more, if size > 1GB) files.
Thus, each database will have numerous data files, essentially one per
table and one per index.
If you rummage around in the files, you can learn quite a lot about
the structuring of things. Each file has a number; that number
corresponds to the OID number in pg_class.
Thus, if you find a file called "17441," then you could find out more
about it by the query
select * from pg_class where oid = 17441;
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