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Re: Making jsonb_agg() faster - Mailing list pgsql-hackers

From Chao Li
Subject Re: Making jsonb_agg() faster
Date
Msg-id 68A1061C-81A5-46AA-AFA9-48294908254C@gmail.com
Whole thread Raw
In response to Re: Making jsonb_agg() faster  (Tom Lane <tgl@sss.pgh.pa.us>)
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On Aug 23, 2025, at 03:11, Tom Lane <tgl@sss.pgh.pa.us> wrote:


v2-0001 takes care of that, and also adopts your suggestion in [1]
about not using two calls of pushJsonbValueScalar where one would do.
I also did a bit more micro-optimization in appendKey, appendValue,
appendElement to avoid redundant copying, because perf testing showed
that appendElement is still a hot-spot for jsonb_agg.  Patches 0002
and 0003 are unchanged.



A small comment. In most of places, JsonbInState is initialized as “JsonbInState ps = {0};”, which is the preferred C style. There are some other places still using memset() to zero out JsonbInState variables. Maybe we can change all memset() usages to “{0}”.

I did a search and found out all memset to change:

diff --git a/src/backend/utils/adt/jsonb.c b/src/backend/utils/adt/jsonb.c
index 0c964052958..9ca501a7a6e 100644
--- a/src/backend/utils/adt/jsonb.c
+++ b/src/backend/utils/adt/jsonb.c
@@ -240,10 +240,10 @@ static inline Datum
 jsonb_from_cstring(char *json, int len, bool unique_keys, Node *escontext)
 {
        JsonLexContext lex;
-       JsonbInState state;
+       JsonbInState state = {0};
        JsonSemAction sem;

-       memset(&state, 0, sizeof(state));
+       //memset(&state, 0, sizeof(state));
        memset(&sem, 0, sizeof(sem));
        makeJsonLexContextCstringLen(&lex, json, len, GetDatabaseEncoding(), true);

@@ -1147,9 +1147,9 @@ to_jsonb(PG_FUNCTION_ARGS)
 Datum
 datum_to_jsonb(Datum val, JsonTypeCategory tcategory, Oid outfuncoid)
 {
-       JsonbInState result;
+       JsonbInState result = {0};

-       memset(&result, 0, sizeof(JsonbInState));
+       //memset(&result, 0, sizeof(JsonbInState));

        datum_to_jsonb_internal(val, false, &result, tcategory, outfuncoid,
                                                        false);
@@ -1162,7 +1162,7 @@ jsonb_build_object_worker(int nargs, const Datum *args, const bool *nulls, const
                                                  bool absent_on_null, bool unique_keys)
 {
        int                     i;
-       JsonbInState result;
+       JsonbInState result = {0};

        if (nargs % 2 != 0)
                ereport(ERROR,
@@ -1172,7 +1172,7 @@ jsonb_build_object_worker(int nargs, const Datum *args, const bool *nulls, const
                                 errhint("The arguments of %s must consist of alternating keys and values.",
                                                 "jsonb_build_object()")));

-       memset(&result, 0, sizeof(JsonbInState));
+       //memset(&result, 0, sizeof(JsonbInState));

        pushJsonbValue(&result, WJB_BEGIN_OBJECT, NULL);
        result.parseState->unique_keys = unique_keys;
@@ -1232,9 +1232,9 @@ jsonb_build_object(PG_FUNCTION_ARGS)
 Datum
 jsonb_build_object_noargs(PG_FUNCTION_ARGS)
 {
-       JsonbInState result;
+       JsonbInState result = {0};

-       memset(&result, 0, sizeof(JsonbInState));
+       //memset(&result, 0, sizeof(JsonbInState));

        pushJsonbValue(&result, WJB_BEGIN_OBJECT, NULL);
        pushJsonbValue(&result, WJB_END_OBJECT, NULL);
@@ -1293,9 +1293,9 @@ jsonb_build_array(PG_FUNCTION_ARGS)
 Datum
 jsonb_build_array_noargs(PG_FUNCTION_ARGS)
 {
-       JsonbInState result;
+       JsonbInState result = {0};

-       memset(&result, 0, sizeof(JsonbInState));
+       //memset(&result, 0, sizeof(JsonbInState));

        pushJsonbValue(&result, WJB_BEGIN_ARRAY, NULL);
        pushJsonbValue(&result, WJB_END_ARRAY, NULL);
@@ -1321,9 +1321,9 @@ jsonb_object(PG_FUNCTION_ARGS)
        int                     in_count,
                                count,
                                i;
-       JsonbInState result;
+       JsonbInState result = {0};

-       memset(&result, 0, sizeof(JsonbInState));
+       //memset(&result, 0, sizeof(JsonbInState));

        pushJsonbValue(&result, WJB_BEGIN_OBJECT, NULL);

@@ -1425,9 +1425,9 @@ jsonb_object_two_arg(PG_FUNCTION_ARGS)
        int                     key_count,
                                val_count,
                                i;
-       JsonbInState result;
+       JsonbInState result = {0};

-       memset(&result, 0, sizeof(JsonbInState));
+       //memset(&result, 0, sizeof(JsonbInState));

        pushJsonbValue(&result, WJB_BEGIN_OBJECT, NULL);

diff --git a/src/backend/utils/adt/jsonpath_exec.c b/src/backend/utils/adt/jsonpath_exec.c
index f0d2378a8cc..4305623b979 100644
--- a/src/backend/utils/adt/jsonpath_exec.c
+++ b/src/backend/utils/adt/jsonpath_exec.c
@@ -2872,7 +2872,7 @@ executeKeyValueMethod(JsonPathExecContext *cxt, JsonPathItem *jsp,
        {
                JsonBaseObjectInfo baseObject;
                JsonbValue      obj;
-               JsonbInState ps;
+               JsonbInState ps = {0};
                Jsonb      *jsonb;

                if (tok != WJB_KEY)
@@ -2886,7 +2886,7 @@ executeKeyValueMethod(JsonPathExecContext *cxt, JsonPathItem *jsp,
                tok = JsonbIteratorNext(&it, &val, true);
                Assert(tok == WJB_VALUE);

-               memset(&ps, 0, sizeof(ps));
+               //memset(&ps, 0, sizeof(ps));

                pushJsonbValue(&ps, WJB_BEGIN_OBJECT, NULL);

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/



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