Create routine able to set single-call SRFs for Materialize mode

Set-returning functions that use the Materialize mode, creating a
tuplestore to include all the tuples returned in a set rather than doing
so in multiple calls, use roughly the same set of steps to prepare
ReturnSetInfo for this job:
- Check if ReturnSetInfo supports returning a tuplestore and if the
materialize mode is enabled.
- Create a tuplestore for all the tuples part of the returned set in the
per-query memory context, stored in ReturnSetInfo->setResult.
- Build a tuple descriptor mostly from get_call_result_type(), then
stored in ReturnSetInfo->setDesc.  Note that there are some cases where
the SRF's tuple descriptor has to be the one specified by the function
caller.

This refactoring is done so as there are (well, should be) no behavior
changes in any of the in-core functions refactored, and the centralized
function that checks and sets up the function's ReturnSetInfo can be
controlled with a set of bits32 options.  Two of them prove to be
necessary now:
- SRF_SINGLE_USE_EXPECTED to use expectedDesc as tuple descriptor, as
expected by the function's caller.
- SRF_SINGLE_BLESS to validate the tuple descriptor for the SRF.

The same initialization pattern is simplified in 28 places per my
count as of src/backend/, shaving up to ~900 lines of code.  These
mostly come from the removal of the per-query initializations and the
sanity checks now grouped in a single location.  There are more
locations that could be simplified in contrib/, that are left for a
follow-up cleanup.

fcc2817, 07daca5 and d61a361 have prepared the areas of the code related
to this change, to ease this refactoring.

Author: Melanie Plageman, Michael Paquier
Reviewed-by: Álvaro Herrera, Justin Pryzby
Discussion: https://postgr.es/m/CAAKRu_azyd1Z3W_r7Ou4sorTjRCs+PxeHw1CWJeXKofkE6TuZg@mail.gmail.com

2 files changed, 73 insertions, 0 deletions

diff --git a/src/backend/utils/fmgr/README b/src/backend/utils/fmgr/README
index 1e4c4b94a95..9d8848106df 100644
--- a/src/backend/utils/fmgr/README
+++ b/src/backend/utils/fmgr/README
@@ -305,6 +305,10 @@ If available, the expected tuple descriptor is passed in ReturnSetInfo;
 in other contexts the expectedDesc field will be NULL.  The function need
 not pay attention to expectedDesc, but it may be useful in special cases.
 
+SetSingleFuncCall() is a helper function able to setup the function's
+ReturnSetInfo for a single call, filling in the Tuplestore and the
+TupleDesc with the proper configuration for Materialize mode.
+
 There is no support for functions accepting sets; instead, the function will
 be called multiple times, once for each element of the input set.
 
diff --git a/src/backend/utils/fmgr/funcapi.c b/src/backend/utils/fmgr/funcapi.c
index 5d913ae08d8..d269662ad8e 100644
--- a/src/backend/utils/fmgr/funcapi.c
+++ b/src/backend/utils/fmgr/funcapi.c
@@ -19,6 +19,7 @@
 #include "catalog/pg_proc.h"
 #include "catalog/pg_type.h"
 #include "funcapi.h"
+#include "miscadmin.h"
 #include "nodes/nodeFuncs.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
@@ -27,6 +28,7 @@
 #include "utils/regproc.h"
 #include "utils/rel.h"
 #include "utils/syscache.h"
+#include "utils/tuplestore.h"
 #include "utils/typcache.h"
 
 
@@ -55,6 +57,73 @@ static TypeFuncClass get_type_func_class(Oid typid, Oid *base_typeid);
 
 
 /*
+ * SetSingleFuncCall
+ *
+ * Helper function to build the state of a set-returning function used
+ * in the context of a single call with materialize mode.  This code
+ * includes sanity checks on ReturnSetInfo, creates the Tuplestore and
+ * the TupleDesc used with the function and stores them into the
+ * function's ReturnSetInfo.
+ *
+ * "flags" can be set to SRF_SINGLE_USE_EXPECTED, to use the tuple
+ * descriptor coming from expectedDesc, which is the tuple descriptor
+ * expected by the caller.  SRF_SINGLE_BLESS can be set to complete the
+ * information associated to the tuple descriptor, which is necessary
+ * in some cases  where the tuple descriptor comes from a transient
+ * RECORD datatype.
+ */
+void
+SetSingleFuncCall(FunctionCallInfo fcinfo, bits32 flags)
+{
+	bool		random_access;
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	Tuplestorestate *tupstore;
+	MemoryContext old_context,
+				per_query_ctx;
+	TupleDesc	stored_tupdesc;
+
+	/* check to see if caller supports returning a tuplestore */
+	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("set-valued function called in context that cannot accept a set")));
+	if (!(rsinfo->allowedModes & SFRM_Materialize) ||
+		((flags & SRF_SINGLE_USE_EXPECTED) != 0 && rsinfo->expectedDesc == NULL))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("materialize mode required, but it is not allowed in this context")));
+
+	/*
+	 * Store the tuplestore and the tuple descriptor in ReturnSetInfo.  This
+	 * must be done in the per-query memory context.
+	 */
+	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
+	old_context = MemoryContextSwitchTo(per_query_ctx);
+
+	/* build a tuple descriptor for our result type */
+	if ((flags & SRF_SINGLE_USE_EXPECTED) != 0)
+		stored_tupdesc = CreateTupleDescCopy(rsinfo->expectedDesc);
+	else
+	{
+		if (get_call_result_type(fcinfo, NULL, &stored_tupdesc) != TYPEFUNC_COMPOSITE)
+			elog(ERROR, "return type must be a row type");
+	}
+
+	/* If requested, bless the tuple descriptor */
+	if ((flags & SRF_SINGLE_BLESS) != 0)
+		BlessTupleDesc(stored_tupdesc);
+
+	random_access = (rsinfo->allowedModes & SFRM_Materialize_Random) != 0;
+
+	tupstore = tuplestore_begin_heap(random_access, false, work_mem);
+	rsinfo->returnMode = SFRM_Materialize;
+	rsinfo->setResult = tupstore;
+	rsinfo->setDesc = stored_tupdesc;
+	MemoryContextSwitchTo(old_context);
+}
+
+
+/*
  * init_MultiFuncCall
  * Create an empty FuncCallContext data structure
  * and do some other basic Multi-function call setup