Why does SPI_connect change the memory context?

Jeff Davis <pgsql@j-davis.com> writes:

SPI_connect() changes the memory context to a newly-created one, and
then SPI_finish() restores it. That seems a bit dangerous because the
caller might not be expecting it. Is there a reason it doesn't just
change to the new memory context as-needed?

Because the expectation is that palloc inside the SPI procedure will
allocate in a procedure-specific context. If the caller isn't expecting
that, they haven't read the documentation, specifically

https://www.postgresql.org/docs/devel/spi-memory.html

which says

<para>
<function>SPI_connect</function> creates a new memory context and
makes it current. <function>SPI_finish</function> restores the
previous current memory context and destroys the context created by
<function>SPI_connect</function>. These actions ensure that
transient memory allocations made inside your C function are
reclaimed at C function exit, avoiding memory leakage.
</para>

regards, tom lane