Limitation relates to memory allocation

Hello!

We encountered an issue related to internal memory allocation limit:
ERROR: invalid memory alloc request size

In the documentation on limits:
https://www.postgresql.org/docs/17/limits.html
the description suggests that only a single field is limited to 1GB,
which could imply that the total tuple size can be larger. So as we
planned to store three columns of 1GB each in a table and attempted to
insert this data, we got the error.

Our research showed that the limit is imposed by the palloc() function,
regardless of whether it is a tuple or not, and if the data is
serialized or dumped, the effective limit can be even lower, typically
around 512MB per row. So for allocations exceeding 1GB, the
palloc_extended() function can be used. Please correct me if I'm wrong.

I prepared a small patch for master, if it's worth clarifying, could you
please review the attachment?

--
Ekaterina Kiryanova
Technical Writer
Postgres Professional
the Russian PostgreSQL Company