Fix SPI's handling of errors during transaction commit.

SPI_commit previously left it up to the caller to recover from any error
occurring during commit.  Since that's complicated and requires use of
low-level xact.c facilities, it's not too surprising that no caller got
it right.  Let's move the responsibility for cleanup into spi.c.  Doing
that requires redefining SPI_commit as starting a new transaction, so
that it becomes equivalent to SPI_commit_and_chain except that you get
default transaction characteristics instead of preserving the prior
transaction's characteristics.  We can make this pretty transparent
API-wise by redefining SPI_start_transaction() as a no-op.  Callers
that expect to do something in between might be surprised, but
available evidence is that no callers do so.

Having made that API redefinition, we can fix this mess by having
SPI_commit[_and_chain] trap errors and start a new, clean transaction
before re-throwing the error.  Likewise for SPI_rollback[_and_chain].
Some cleanup is also needed in AtEOXact_SPI, which was nowhere near
smart enough to deal with SPI contexts nested inside a committing
context.

While plperl and pltcl need no changes beyond removing their now-useless
SPI_start_transaction() calls, plpython needs some more work because it
hadn't gotten the memo about catching commit/rollback errors in the
first place.  Such an error resulted in longjmp'ing out of the Python
interpreter, which leaks Python stack entries at present and is reported
to crash Python 3.11 altogether.  Add the missing logic to catch such
errors and convert them into Python exceptions.

This is a back-patch of commit 2e517818f.  That's now aged long enough
to reduce the concerns about whether it will break something, and we
do need to ensure that supported branches will work with Python 3.11.

Peter Eisentraut and Tom Lane

Discussion: https://postgr.es/m/3375ffd8-d71c-2565-e348-a597d6e739e3@enterprisedb.com
Discussion: https://postgr.es/m/17416-ed8fe5d7213d6c25@postgresql.org

1 files changed, 30 insertions, 0 deletions

diff --git a/src/pl/plpython/sql/plpython_transaction.sql b/src/pl/plpython/sql/plpython_transaction.sql
index 33b37e5b7fc..68588d9fb02 100644
--- a/src/pl/plpython/sql/plpython_transaction.sql
+++ b/src/pl/plpython/sql/plpython_transaction.sql
@@ -148,5 +148,35 @@ SELECT * FROM test1;
 SELECT * FROM pg_cursors;
 
 
+-- check handling of an error during COMMIT
+CREATE TABLE testpk (id int PRIMARY KEY);
+CREATE TABLE testfk(f1 int REFERENCES testpk DEFERRABLE INITIALLY DEFERRED);
+
+DO LANGUAGE plpythonu $$
+# this insert will fail during commit:
+plpy.execute("INSERT INTO testfk VALUES (0)")
+plpy.commit()
+plpy.warning('should not get here')
+$$;
+
+SELECT * FROM testpk;
+SELECT * FROM testfk;
+
+DO LANGUAGE plpythonu $$
+# this insert will fail during commit:
+plpy.execute("INSERT INTO testfk VALUES (0)")
+try:
+    plpy.commit()
+except Exception as e:
+    plpy.info('sqlstate: %s' % (e.sqlstate))
+# these inserts should work:
+plpy.execute("INSERT INTO testpk VALUES (1)")
+plpy.execute("INSERT INTO testfk VALUES (1)")
+$$;
+
+SELECT * FROM testpk;
+SELECT * FROM testfk;
+
+
 DROP TABLE test1;
 DROP TABLE test2;