Re: Old-client/new-server...issues?

Craig Ringer <craig(at)postnewspapers(dot)com(dot)au> writes:
> On 7/06/2011 8:32 AM, Steve Crawford wrote:
>> I am working on my final 7.4 -> 9.0 upgrade. Data-type (auto-coalesce
>> and foreign-key), query and encoding issues are resolved. Dump/restore
>> is tested. But...
>>
>> I have a few old client systems that are difficult/infeasible to update.
>> I know the recommended procedure is to update clients ahead of server
>> but what problems am I likely to encounter connecting to a 9.0 server
>> from a 7.4 client?

> Reliance on implicit casts to/from text in queries may be a problem.

> You could also have issues if the clients rely on metadata obtained from
> the database - for example, enumerating columns in a table or listing
> tables. I know this has been an issue when using older JDBC drivers
> against newer servers, and wouldn't be too surprised if similar issues
> existed with libpq.

libpq itself is pretty metadata-ignorant. Higher-level stuff such as
python or perl DBI interfaces (or JDBC, as Craig says) would pose much
more risk.

At the same time, if you are sticking with a 7.4-era libpq, you're
missing literally years worth of bug fixes ... and I think the
compatibility risks associated with an update there are pretty minimal
compared to what you're already buying into with the server-side upgrade.

So my advice would be to try to relink all your old apps against more
modern versions of libpq as well as any higher-level client drivers you
are using.

regards, tom lane