pgsql: Avoid unexpected changes of CurrentResourceOwner and CurrentMemo

Avoid unexpected changes of CurrentResourceOwner and CurrentMemoryContext

Users of logical decoding can encounter an unexpected change of
CurrentResourceOwner and CurrentMemoryContext. The problem is that,
unlike other call sites of RollbackAndReleaseCurrentSubTransaction(), in
reorderbuffer.c we fail to restore the original values of these global
variables after being clobbered by subtransaction abort. This patch
saves the values prior to the call and restores them eventually.

In addition, logical.c and logicalfuncs.c had a hack to restore resource
owner, presumably because of lack of this restore. Remove that.
Instead, because the test coverage here is not very consistent, add an
Assert() to ensure that the resowner is kept identical; this would make
it easy to detect other cases of bugs were we fail to restore resowner
properly. This could be removed later.

This is arguably an old bug, but there appears to be no reason to
backpatch it and it's risky to do so, so refrain for now.

Author: Antonin Houska <ah(at)cybertec(dot)at>
Reported-by: Mihail Nikalayeu <mihailnikalayeu(at)gmail(dot)com>
Reviewed-by: Euler Taveira <euler(at)eulerto(dot)com>
Discussion: https://postgr.es/m/119497.1756892972@localhost

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/7dcea51c2a4dcf7c512bbd4f618d1d3620f9d3d7

Modified Files
--------------
src/backend/replication/logical/logical.c | 19 +++++++++++--------
src/backend/replication/logical/logicalfuncs.c | 19 +++++++++++--------
src/backend/replication/logical/reorderbuffer.c | 15 +++++++++++++++
3 files changed, 37 insertions(+), 16 deletions(-)