pgsql: Document changes in large-object privilege checking.
Document changes in large-object privilege checking.
Commit 5ecc0d738 removed the hard-wired superuser checks in lo_import
and lo_export in favor of protecting them with SQL permissions, but
failed to adjust the documentation to match. Fix that, and add a
<caution> paragraph pointing out the nontrivial security hazards
involved with actually granting such permissions. (It's still better
than ALLOW_DANGEROUS_LO_FUNCTIONS, though.)
Also, commit ae20b23a9 caused large object read/write privilege to
be checked during lo_open() rather than in the actual read or write
calls. Document that.