Improve the efficiency of certain jsonb get operations.

Instead of iterating over jsonb structures, use the inbuilt functions
findJsonbValueFromContainerLen() and getIthJsonbValueFromContainer() to
extract values directly. These functions use algorithms that are O(n log
n) and O(1) respectively, whereas iterating is O(n), so we should see
considerable speedup here.

Teodor Sigaev.

src/backend/utils/adt/jsonfuncs.c

@@ -466,12 +466,8 @@ Datum
 jsonb_object_field(PG_FUNCTION_ARGS)
 {
 	Jsonb	   *jb = PG_GETARG_JSONB(0);
-	char	   *key = text_to_cstring(PG_GETARG_TEXT_P(1));
-	int			klen = strlen(key);
-	JsonbIterator *it;
-	JsonbValue	v;
-	int			r;
-	bool		skipNested = false;
+	text	   *key = PG_GETARG_TEXT_PP(1);
+	JsonbValue *v;
 
 	if (JB_ROOT_IS_SCALAR(jb))
 		ereport(ERROR,
@@ -484,25 +480,11 @@ jsonb_object_field(PG_FUNCTION_ARGS)
 
 	Assert(JB_ROOT_IS_OBJECT(jb));
 
-	it = JsonbIteratorInit(&jb->root);
-
-	while ((r = JsonbIteratorNext(&it, &v, skipNested)) != WJB_DONE)
-	{
-		skipNested = true;
+	v = findJsonbValueFromContainerLen(&jb->root, JB_FOBJECT,
+									   VARDATA_ANY(key), VARSIZE_ANY_EXHDR(key));
 
-		if (r == WJB_KEY)
-		{
-			if (klen == v.val.string.len && strncmp(key, v.val.string.val, klen) == 0)
-			{
-				/*
-				 * The next thing the iterator fetches should be the value, no
-				 * matter what shape it is.
-				 */
-				(void) JsonbIteratorNext(&it, &v, skipNested);
-				PG_RETURN_JSONB(JsonbValueToJsonb(&v));
-			}
-		}
-	}
+	if (v != NULL)
+		PG_RETURN_JSONB(JsonbValueToJsonb(v));
 
 	PG_RETURN_NULL();
 }
@@ -527,12 +509,8 @@ Datum
 jsonb_object_field_text(PG_FUNCTION_ARGS)
 {
 	Jsonb	   *jb = PG_GETARG_JSONB(0);
-	char	   *key = text_to_cstring(PG_GETARG_TEXT_P(1));
-	int			klen = strlen(key);
-	JsonbIterator *it;
-	JsonbValue	v;
-	int			r;
-	bool		skipNested = false;
+	text	   *key = PG_GETARG_TEXT_PP(1);
+	JsonbValue *v;
 
 	if (JB_ROOT_IS_SCALAR(jb))
 		ereport(ERROR,
@@ -545,47 +523,41 @@ jsonb_object_field_text(PG_FUNCTION_ARGS)
 
 	Assert(JB_ROOT_IS_OBJECT(jb));
 
-	it = JsonbIteratorInit(&jb->root);
+	v = findJsonbValueFromContainerLen(&jb->root, JB_FOBJECT,
+									   VARDATA_ANY(key), VARSIZE_ANY_EXHDR(key));
 
-	while ((r = JsonbIteratorNext(&it, &v, skipNested)) != WJB_DONE)
+	if (v != NULL)
 	{
-		skipNested = true;
+		text	   *result = NULL;
 
-		if (r == WJB_KEY)
+		switch(v->type)
 		{
-			if (klen == v.val.string.len && strncmp(key, v.val.string.val, klen) == 0)
-			{
-				text	   *result;
-
-				/*
-				 * The next thing the iterator fetches should be the value, no
-				 * matter what shape it is.
-				 */
-				r = JsonbIteratorNext(&it, &v, skipNested);
-
-				/*
-				 * if it's a scalar string it needs to be de-escaped,
-				 * otherwise just return the text
-				 */
-				if (v.type == jbvString)
+			case jbvNull:
+				break;
+			case jbvBool:
+				result = cstring_to_text(v->val.boolean ? "true" : "false");
+				break;
+			case jbvString:
+				result = cstring_to_text_with_len(v->val.string.val, v->val.string.len);
+				break;
+			case jbvNumeric:
+				result = cstring_to_text(DatumGetCString(DirectFunctionCall1(numeric_out,
+																			 PointerGetDatum(v->val.numeric))));
+				break;
+			case jbvBinary:
 				{
-					result = cstring_to_text_with_len(v.val.string.val, v.val.string.len);
-				}
-				else if (v.type == jbvNull)
-				{
-					PG_RETURN_NULL();
-				}
-				else
-				{
-					StringInfo	jtext = makeStringInfo();
-					Jsonb	   *tjb = JsonbValueToJsonb(&v);
+					StringInfo  jtext = makeStringInfo();
 
-					(void) JsonbToCString(jtext, &tjb->root , -1);
+					(void) JsonbToCString(jtext, v->val.binary.data, -1);
 					result = cstring_to_text_with_len(jtext->data, jtext->len);
 				}
-				PG_RETURN_TEXT_P(result);
-			}
+				break;
+			default:
+				elog(ERROR, "Wrong jsonb type: %d", v->type);
 		}
+
+		if (result)
+			PG_RETURN_TEXT_P(result);
 	}
 
 	PG_RETURN_NULL();
@@ -611,11 +583,7 @@ jsonb_array_element(PG_FUNCTION_ARGS)
 {
 	Jsonb	   *jb = PG_GETARG_JSONB(0);
 	int			element = PG_GETARG_INT32(1);
-	JsonbIterator *it;
-	JsonbValue	v;
-	int			r;
-	bool		skipNested = false;
-	int			element_number = 0;
+	JsonbValue *v;
 
 	if (JB_ROOT_IS_SCALAR(jb))
 		ereport(ERROR,
@@ -628,18 +596,9 @@ jsonb_array_element(PG_FUNCTION_ARGS)
 
 	Assert(JB_ROOT_IS_ARRAY(jb));
 
-	it = JsonbIteratorInit(&jb->root);
-
-	while ((r = JsonbIteratorNext(&it, &v, skipNested)) != WJB_DONE)
-	{
-		skipNested = true;
-
-		if (r == WJB_ELEM)
-		{
-			if (element_number++ == element)
-				PG_RETURN_JSONB(JsonbValueToJsonb(&v));
-		}
-	}
+	v = getIthJsonbValueFromContainer(&jb->root, element);
+	if (v != NULL)
+		PG_RETURN_JSONB(JsonbValueToJsonb(v));
 
 	PG_RETURN_NULL();
 }
@@ -664,12 +623,7 @@ jsonb_array_element_text(PG_FUNCTION_ARGS)
 {
 	Jsonb	   *jb = PG_GETARG_JSONB(0);
 	int			element = PG_GETARG_INT32(1);
-	JsonbIterator *it;
-	JsonbValue	v;
-	int			r;
-	bool		skipNested = false;
-	int			element_number = 0;
-
+	JsonbValue *v;
 
 	if (JB_ROOT_IS_SCALAR(jb))
 		ereport(ERROR,
@@ -682,41 +636,39 @@ jsonb_array_element_text(PG_FUNCTION_ARGS)
 
 	Assert(JB_ROOT_IS_ARRAY(jb));
 
-	it = JsonbIteratorInit(&jb->root);
-
-	while ((r = JsonbIteratorNext(&it, &v, skipNested)) != WJB_DONE)
+	v = getIthJsonbValueFromContainer(&jb->root, element);
+	if (v != NULL)
 	{
-		skipNested = true;
+		text	   *result = NULL;
 
-		if (r == WJB_ELEM)
+		switch(v->type)
 		{
-			if (element_number++ == element)
-			{
-				/*
-				 * if it's a scalar string it needs to be de-escaped,
-				 * otherwise just return the text
-				 */
-				text	   *result;
-
-				if (v.type == jbvString)
-				{
-					result = cstring_to_text_with_len(v.val.string.val, v.val.string.len);
-				}
-				else if (v.type == jbvNull)
-				{
-					PG_RETURN_NULL();
-				}
-				else
+			case jbvNull:
+				break;
+			case jbvBool:
+				result = cstring_to_text(v->val.boolean ? "true" : "false");
+				break;
+			case jbvString:
+				result = cstring_to_text_with_len(v->val.string.val, v->val.string.len);
+				break;
+			case jbvNumeric:
+				result = cstring_to_text(DatumGetCString(DirectFunctionCall1(numeric_out,
+											PointerGetDatum(v->val.numeric))));
+				break;
+			case jbvBinary:
 				{
-					StringInfo	jtext = makeStringInfo();
-					Jsonb	   *tjb = JsonbValueToJsonb(&v);
+					StringInfo  jtext = makeStringInfo();
 
-					(void) JsonbToCString(jtext, &tjb->root, -1);
+					(void) JsonbToCString(jtext, v->val.binary.data, -1);
 					result = cstring_to_text_with_len(jtext->data, jtext->len);
 				}
-				PG_RETURN_TEXT_P(result);
-			}
+				break;
+			default:
+				elog(ERROR, "Wrong jsonb type: %d", v->type);
 		}
+
+		if (result)
+			PG_RETURN_TEXT_P(result);
 	}
 
 	PG_RETURN_NULL();