ERROR: tuple concurrently updated

Greetings,

Subject pretty much says it all. I've put up with this error in the
past when it has caused me trouble but it's now starting to hit our
clients on occation which is just unacceptable.

The way I've seen it happen, and this is just empirically so I'm not
sure that it's exactly right, is something like this:

Running with pg_autovacuum on the system
Run a long-running PL/PgSQL function which creates tables
Wait for some sort of overlap, and the PL/PgSQL function dies with the
above error.

I've also seen it happen when I've got a long-running PL/PgSQL
function going and I'm creating tables in another back-end.

From a prior discussion I *think* the issue is the lack of
versioning/visibility information in the SysCache which means that if
the long-running function attempts to look-up data about a table which
was created *after* the long-running function started but was put into
the common SysCache by another backend, the long-running function gets
screwed by the 'tuple concurrently updated' query and ends up failing
and being rolled back.

If this is correct then the solution seems to be either add versioning
to the SysCache data, or have an overall 'this SysCache is only good
for data past transaction X' so that a backend which is prior to that
version could just accept that it can't use the SysCache and fall back
to accessing the data directly (if that's possible). I'm not very
familiar with the way the SysCache system is envisioned but I'm not a
terrible programmer (imv anyway) and given some direction on the
correct approach to solving this problem I'd be happy to spend some
time working on it. I'd *really* like to see this error just go away
completely for all non-broken use-cases.

Thanks,

Stephen