Optimize jsonb returning, Json allocation

Author: Nikita Glukhov

src/backend/utils/adt/jsonb_util.c

@@ -2715,6 +2715,9 @@ DatumGetJsonbPC(Datum datum, Json *tmp, bool copy)
 			datum = PointerGetDatum(pg_detoast_datum_copy(src));
 	}
 
+	if (!jsonb_partial_decompression)
+		return DatumGetJson(datum, &jsonbContainerOps, tmp);
+
 	CompressedDatumInit(&cd, datum);
 
 	if (!cd.compressed)

src/include/utils/json_generic.h

@@ -110,7 +110,7 @@ typedef JsonContainer JsonbContainer;
 #else
 #define PG_GETARG_JSONB_P(n)		DatumGetJsonbP(PG_GETARG_DATUM(n), alloca(sizeof(Json)), false) /* FIXME conditional alloca() */
 #endif
-#define PG_GETARG_JSONB_PC(n)		DatumGetJsonbPC(PG_GETARG_DATUM(n), alloca(sizeof(Json)), false) /* FIXME conditional alloca() */
+#define PG_GETARG_JSONB_PC(n)		DatumGetJsonbPC(PG_GETARG_DATUM(n), alloca(JsonAllocSize(16)) /* FIXME sizeof CompressedJsonb */, false)
 #define PG_GETARG_JSONB_P_COPY(x)	DatumGetJsonbPCopy(PG_GETARG_DATUM(x))
 
 #define PG_FREE_IF_COPY_JSONB(json, n) JsonFree(json)