Simplify code by getting rid of SPI_push, SPI_pop, SPI_restore_connection.

The idea behind SPI_push was to allow transitioning back into an
"unconnected" state when a SPI-using procedure calls unrelated code that
might or might not invoke SPI.  That sounds good, but in practice the only
thing it does for us is to catch cases where a called SPI-using function
forgets to call SPI_connect --- which is a highly improbable failure mode,
since it would be exposed immediately by direct testing of said function.
As against that, we've had multiple bugs induced by forgetting to call
SPI_push/SPI_pop around code that might invoke SPI-using functions; these
are much harder to catch and indeed have gone undetected for years in some
cases.  And we've had to band-aid around some problems of this ilk by
introducing conditional push/pop pairs in some places, which really kind
of defeats the purpose altogether; if we can't draw bright lines between
connected and unconnected code, what's the point?

Hence, get rid of SPI_push[_conditional], SPI_pop[_conditional], and the
underlying state variable _SPI_curid.  It turns out SPI_restore_connection
can go away too, which is a nice side benefit since it was never more than
a kluge.  Provide no-op macros for the deleted functions so as to avoid an
API break for external modules.

A side effect of this removal is that SPI_palloc and allied functions no
longer permit being called when unconnected; they'll throw an error
instead.  The apparent usefulness of the previous behavior was a mirage
as well, because it was depended on by only a few places (which I fixed in
preceding commits), and it posed a risk of allocations being unexpectedly
long-lived if someone forgot a SPI_push call.

Discussion: <20808.1478481403@sss.pgh.pa.us>

1 files changed, 0 insertions, 6 deletions

diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index b144920ec65..057c3bfd7c1 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -2644,8 +2644,6 @@ schema_to_xml_internal(Oid nspid, const char *xmlschema, bool nulls,
 
 	relid_list = schema_get_xml_visible_tables(nspid);
 
-	SPI_push();
-
 	foreach(cell, relid_list)
 	{
 		Oid			relid = lfirst_oid(cell);
@@ -2658,7 +2656,6 @@ schema_to_xml_internal(Oid nspid, const char *xmlschema, bool nulls,
 		appendStringInfoChar(result, '\n');
 	}
 
-	SPI_pop();
 	SPI_finish();
 
 	xmldata_root_element_end(result, xmlsn);
@@ -2822,8 +2819,6 @@ database_to_xml_internal(const char *xmlschema, bool nulls,
 
 	nspid_list = database_get_xml_visible_schemas();
 
-	SPI_push();
-
 	foreach(cell, nspid_list)
 	{
 		Oid			nspid = lfirst_oid(cell);
@@ -2836,7 +2831,6 @@ database_to_xml_internal(const char *xmlschema, bool nulls,
 		appendStringInfoChar(result, '\n');
 	}
 
-	SPI_pop();
 	SPI_finish();
 
 	xmldata_root_element_end(result, xmlcn);