I am using version 8.2.6. I remember the problem with large databases. That happens when the backup file itself exceeded 2GB in size thus causing an error. That is not the case here as my backup file is well short of 2GB, and I believe that bug was fixed in 8.2.3 anyway.
This is a strange error because I was able to backup this database just as recently as last week. Since then I reimported all the hands fresh into an empty database to take advantage of the patch that makes separate levels for NL with cap and standard NL. So this database is the same size and is freshly created. The only thing I did to this one that I hadn't done to the original database for a while is the clustering of various indexes as described in a post you surely are familiar with. Maybe the clustering has someone screwed up the database. I guess the only way to know is to reimport all the hands again and then try to backup without clustering. I hate the thought of that as the database has 2.5 million hands and it took 3 days to import everything.
Googling this memory alloc request size error I find several hits but most of it is way to technical for me to follow. Here's one hit.
http://archives.postgresql.org/pgsql-ad ... g00117.php