Re: old JDBC driver (8.1-JDBC3) can connect to postgresql 9.x ?

On Mon, Jan 16, 2017 at 6:05 PM, itoshun001(at)efeel(dot)to <itoshun001(at)efeel(dot)to>
wrote:

> Hi Jorge
>
> Thank you for your accurate answers and kind understanding for our
> situation.
> Now I understand below and these info is very useful for our team !
>
> - the old driver(8.1-404 JDBC3) technically can connect to postgresql
> 9.3 but some new features should not be available, and we won't get the
> bugfixes of later version.
>

​Yes technically, but as John points out ​you could hit a schema catalog
change so while it *might* work, there is a chance to hit a problem with
pg_catalog updates, the pg_catalog is an internal postgresql table that
contains many info consumed by the pgjdbc driver and newer versions of the
driver can handle all these variations, so for instance the pgjdbc driver
9.3 Build 1103 can connect without problems to older postgresql versions
like the one you are using (8.3) and it can connect to newer postgresql
versions like 9.3.

For many years the pgjdbc driver followed the versions of the server to
declare some kind of compatibility, basically it means that the version you
are using (8.1-404 JDBC3) was essentially for postgresql 8.1 and older, but
you are using it for postgresql 8.3 and it works (for you). From the
version 9.4.x of the driver that is no longer the case, and the current
version 9.4.1212 works on PostgreSQL 9.6 too.

>
> - the driver should be highly compatible with earlier versions, and if
> our web app is using standard jdbc, then it should be practically
> transparent the change (we don't even need to recompile).
>

Yes, it should work for postgresql 8.3 and postgresql 9.3 (and everything
between) that means that you should be using (based on the Java 5 version)
the PgJDBC 9.3 Build 1103 and not the 8.1-404, but as I said before, always
test for potential regressions.

>
> One more question which might be last question....
>
> (Q) My understanding below is correct ??
>
> Versions of jdbc driver that supported Java 5 can't connect to
> postgresql 9.4 or later
> because
> - the versions of jdbc driver don't support JDBC 4, 41 and 42
> - the versions of postreqsql don't support JDBC3
>

​​Let me be cristal clear​, it *might* work ​but again, you might hit a
problem with pg_catalog updates and others compatibility issues, so is NOT
recomeded to use an older driver version to connect to a newer postgresql
version, you should always try to use the latest driver. For example I have
a web app that is still on PostgreSQL 9.1 but it's using the latest driver
version 9.4.1212. What I mean is that is better to have a new jdbc driver
connecting to an older postgresql instance than the opposite.

To clarify your points, PostgreSQL knows nothing about Java or JDBC, the
PgJDBC driver is a pure Java driver that implements the native protocol of
PostgreSQL, so PgJDBC "talks" in the PostgreSQL native language (the binary
or text protocol that postgres understand). So when a new version of
PostgreSQL comes out, the driver has to "understand" the new or changed
stuff so an older version of the driver do not recognize the changed stuff
and there might hit a compatibility issue.

And as John said, Java 5 is obsolete, my recomendation is to try upgrading
the Java version, at least to Java 6, Java is for the most part backward
compatible, so you can use a new Java Runtime for a Java 5 compiled app.

Then try to update the PgJDBC driver to the latest version, and finally try
to upgrade the PostgreSQL server to a supported version.

As always, test, test and do more test for any potential problem.

>
> Best regards,
> itoshun
>