Transaction control in PL procedures

In each of the supplied procedural languages (PL/pgSQL, PL/Perl,
PL/Python, PL/Tcl), add language-specific commit and rollback
functions/commands to control transactions in procedures in that
language.  Add similar underlying functions to SPI.  Some additional
cleanup so that transaction commit or abort doesn't blow away data
structures still used by the procedure call.  Add execution context
tracking to CALL and DO statements so that transaction control commands
can only be issued in top-level procedure and block calls, not function
calls or other procedure or block calls.

- SPI

Add a new function SPI_connect_ext() that is like SPI_connect() but
allows passing option flags.  The only option flag right now is
SPI_OPT_NONATOMIC.  A nonatomic SPI connection can execute transaction
control commands, otherwise it's not allowed.  This is meant to be
passed down from CALL and DO statements which themselves know in which
context they are called.  A nonatomic SPI connection uses different
memory management.  A normal SPI connection allocates its memory in
TopTransactionContext.  For nonatomic connections we use PortalContext
instead.  As the comment in SPI_connect_ext() (previously SPI_connect())
indicates, one could potentially use PortalContext in all cases, but it
seems safest to leave the existing uses alone, because this stuff is
complicated enough already.

SPI also gets new functions SPI_start_transaction(), SPI_commit(), and
SPI_rollback(), which can be used by PLs to implement their transaction
control logic.

- portalmem.c

Some adjustments were made in the code that cleans up portals at
transaction abort.  The portal code could already handle a command
*committing* a transaction and continuing (e.g., VACUUM), but it was not
quite prepared for a command *aborting* a transaction and continuing.

In AtAbort_Portals(), remove the code that marks an active portal as
failed.  As the comment there already predicted, this doesn't work if
the running command wants to keep running after transaction abort.  And
it's actually not necessary, because pquery.c is careful to run all
portal code in a PG_TRY block and explicitly runs MarkPortalFailed() if
there is an exception.  So the code in AtAbort_Portals() is never used
anyway.

In AtAbort_Portals() and AtCleanup_Portals(), we need to be careful not
to clean up active portals too much.  This mirrors similar code in
PreCommit_Portals().

- PL/Perl

Gets new functions spi_commit() and spi_rollback()

- PL/pgSQL

Gets new commands COMMIT and ROLLBACK.

Update the PL/SQL porting example in the documentation to reflect that
transactions are now possible in procedures.

- PL/Python

Gets new functions plpy.commit and plpy.rollback.

- PL/Tcl

Gets new commands commit and rollback.

Reviewed-by: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>

1 files changed, 44 insertions, 3 deletions

diff --git a/src/backend/commands/functioncmds.c b/src/backend/commands/functioncmds.c
index ea08c3237c1..df87dfeb543 100644
--- a/src/backend/commands/functioncmds.c
+++ b/src/backend/commands/functioncmds.c
@@ -65,6 +65,7 @@
 #include "utils/fmgroids.h"
 #include "utils/guc.h"
 #include "utils/lsyscache.h"
+#include "utils/memutils.h"
 #include "utils/rel.h"
 #include "utils/syscache.h"
 #include "utils/tqual.h"
@@ -2136,9 +2137,11 @@ IsThereFunctionInNamespace(const char *proname, int pronargs,
 /*
  * ExecuteDoStmt
  *		Execute inline procedural-language code
+ *
+ * See at ExecuteCallStmt() about the atomic argument.
  */
 void
-ExecuteDoStmt(DoStmt *stmt)
+ExecuteDoStmt(DoStmt *stmt, bool atomic)
 {
 	InlineCodeBlock *codeblock = makeNode(InlineCodeBlock);
 	ListCell   *arg;
@@ -2200,6 +2203,7 @@ ExecuteDoStmt(DoStmt *stmt)
 	codeblock->langOid = HeapTupleGetOid(languageTuple);
 	languageStruct = (Form_pg_language) GETSTRUCT(languageTuple);
 	codeblock->langIsTrusted = languageStruct->lanpltrusted;
+	codeblock->atomic = atomic;
 
 	if (languageStruct->lanpltrusted)
 	{
@@ -2236,9 +2240,28 @@ ExecuteDoStmt(DoStmt *stmt)
 
 /*
  * Execute CALL statement
+ *
+ * Inside a top-level CALL statement, transaction-terminating commands such as
+ * COMMIT or a PL-specific equivalent are allowed.  The terminology in the SQL
+ * standard is that CALL establishes a non-atomic execution context.  Most
+ * other commands establish an atomic execution context, in which transaction
+ * control actions are not allowed.  If there are nested executions of CALL,
+ * we want to track the execution context recursively, so that the nested
+ * CALLs can also do transaction control.  Note, however, that for example in
+ * CALL -> SELECT -> CALL, the second call cannot do transaction control,
+ * because the SELECT in between establishes an atomic execution context.
+ *
+ * So when ExecuteCallStmt() is called from the top level, we pass in atomic =
+ * false (recall that that means transactions = yes).  We then create a
+ * CallContext node with content atomic = false, which is passed in the
+ * fcinfo->context field to the procedure invocation.  The language
+ * implementation should then take appropriate measures to allow or prevent
+ * transaction commands based on that information, e.g., call
+ * SPI_connect_ext(SPI_OPT_NONATOMIC).  The language should also pass on the
+ * atomic flag to any nested invocations to CALL.
  */
 void
-ExecuteCallStmt(ParseState *pstate, CallStmt *stmt)
+ExecuteCallStmt(ParseState *pstate, CallStmt *stmt, bool atomic)
 {
 	List	   *targs;
 	ListCell   *lc;
@@ -2249,6 +2272,8 @@ ExecuteCallStmt(ParseState *pstate, CallStmt *stmt)
 	AclResult   aclresult;
 	FmgrInfo	flinfo;
 	FunctionCallInfoData fcinfo;
+	CallContext *callcontext;
+	HeapTuple	tp;
 
 	targs = NIL;
 	foreach(lc, stmt->funccall->args)
@@ -2284,8 +2309,24 @@ ExecuteCallStmt(ParseState *pstate, CallStmt *stmt)
 							   FUNC_MAX_ARGS,
 							   FUNC_MAX_ARGS)));
 
+	callcontext = makeNode(CallContext);
+	callcontext->atomic = atomic;
+
+	/*
+	 * If proconfig is set we can't allow transaction commands because of the
+	 * way the GUC stacking works: The transaction boundary would have to pop
+	 * the proconfig setting off the stack.  That restriction could be lifted
+	 * by redesigning the GUC nesting mechanism a bit.
+	 */
+	tp = SearchSysCache1(PROCOID, ObjectIdGetDatum(fexpr->funcid));
+	if (!HeapTupleIsValid(tp))
+		elog(ERROR, "cache lookup failed for function %u", fexpr->funcid);
+	if (!heap_attisnull(tp, Anum_pg_proc_proconfig))
+		callcontext->atomic = true;
+	ReleaseSysCache(tp);
+
 	fmgr_info(fexpr->funcid, &flinfo);
-	InitFunctionCallInfoData(fcinfo, &flinfo, nargs, fexpr->inputcollid, NULL, NULL);
+	InitFunctionCallInfoData(fcinfo, &flinfo, nargs, fexpr->inputcollid, (Node *) callcontext, NULL);
 
 	i = 0;
 	foreach (lc, fexpr->args)