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

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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>
This commit is contained in:
Tom Lane
2016-11-08 17:39:45 -05:00
parent 577f0bdd2b
commit 1833f1a1c3
12 changed files with 105 additions and 493 deletions
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13
src/backend/utils/cache/plancache.c vendored
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@ -53,7 +53,6 @@
#include "access/transam.h"
#include "catalog/namespace.h"
#include "executor/executor.h"
#include "executor/spi.h"
#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/cost.h"
@ -878,7 +877,6 @@ BuildCachedPlan(CachedPlanSource *plansource, List *qlist,
CachedPlan *plan;
List *plist;
bool snapshot_set;
bool spi_pushed;
bool is_transient;
MemoryContext plan_context;
MemoryContext oldcxt = CurrentMemoryContext;
@ -926,22 +924,11 @@ BuildCachedPlan(CachedPlanSource *plansource, List *qlist,
snapshot_set = true;
}
/*
* The planner may try to call SPI-using functions, which causes a problem
* if we're already inside one. Rather than expect all SPI-using code to
* do SPI_push whenever a replan could happen, it seems best to take care
* of the case here.
*/
spi_pushed = SPI_push_conditional();
/*
* Generate the plan.
*/
plist = pg_plan_queries(qlist, plansource->cursor_options, boundParams);
/* Clean up SPI state */
SPI_pop_conditional(spi_pushed);
/* Release snapshot if we got one */
if (snapshot_set)
PopActiveSnapshot();