fix the calculation of incremental-sum (#15468)

* fix the calculation of incremental-sum

* for query planning use at least 400 points

2 files changed, 20 insertions, 13 deletions

diff --git a/web/api/queries/incremental_sum/incremental_sum.h b/web/api/queries/incremental_sum/incremental_sum.h
index dd6483b2ca..f110c58611 100644
--- a/web/api/queries/incremental_sum/incremental_sum.h
+++ b/web/api/queries/incremental_sum/incremental_sum.h
@@ -12,19 +12,20 @@ struct tg_incremental_sum {
     size_t count;
 };
 
-static inline void tg_incremental_sum_create(RRDR *r, const char *options __maybe_unused) {
-    r->time_grouping.data = onewayalloc_callocz(r->internal.owa, 1, sizeof(struct tg_incremental_sum));
-}
-
 // resets when switches dimensions
 // so, clear everything to restart
 static inline void tg_incremental_sum_reset(RRDR *r) {
     struct tg_incremental_sum *g = (struct tg_incremental_sum *)r->time_grouping.data;
-    g->first = 0;
-    g->last = 0;
+    g->first = NAN;
+    g->last = NAN;
     g->count = 0;
 }
 
+static inline void tg_incremental_sum_create(RRDR *r, const char *options __maybe_unused) {
+    r->time_grouping.data = onewayalloc_mallocz(r->internal.owa, sizeof(struct tg_incremental_sum));
+    tg_incremental_sum_reset(r);
+}
+
 static inline void tg_incremental_sum_free(RRDR *r) {
     onewayalloc_freez(r->internal.owa, r->time_grouping.data);
     r->time_grouping.data = NULL;
@@ -34,7 +35,11 @@ static inline void tg_incremental_sum_add(RRDR *r, NETDATA_DOUBLE value) {
     struct tg_incremental_sum *g = (struct tg_incremental_sum *)r->time_grouping.data;
 
     if(unlikely(!g->count)) {
-        g->first = value;
+        if(isnan(g->first))
+            g->first = value;
+        else
+            g->last = value;
+
         g->count++;
     }
     else {
@@ -48,19 +53,16 @@ static inline NETDATA_DOUBLE tg_incremental_sum_flush(RRDR *r, RRDR_VALUE_FLAGS
 
     NETDATA_DOUBLE value;
 
-    if(unlikely(!g->count)) {
+    if(unlikely(!g->count || isnan(g->first) || isnan(g->last))) {
         value = 0.0;
         *rrdr_value_options_ptr |= RRDR_VALUE_EMPTY;
     }
-    else if(unlikely(g->count == 1)) {
-        value = 0.0;
-    }
     else {
         value = g->last - g->first;
     }
 
-    g->first = 0.0;
-    g->last = 0.0;
+    g->first = g->last;
+    g->last = NAN;
     g->count = 0;
 
     return value;
diff --git a/web/api/queries/query.c b/web/api/queries/query.c
index 74a925bc3d..ef8ee7e623 100644
--- a/web/api/queries/query.c
+++ b/web/api/queries/query.c
@@ -17,6 +17,7 @@
 #include "percentile/percentile.h"
 #include "trimmed_mean/trimmed_mean.h"
 
+#define QUERY_PLAN_MIN_POINTS 400
 #define POINTS_TO_EXPAND_QUERY 5
 
 // ----------------------------------------------------------------------------
@@ -996,6 +997,10 @@ static size_t query_metric_best_tier_for_timeframe(QUERY_METRIC *qm, time_t afte
     if(unlikely(after_wanted == before_wanted || points_wanted <= 0))
         return query_metric_first_working_tier(qm);
 
+    if(points_wanted < QUERY_PLAN_MIN_POINTS)
+        // when selecting tiers, aim for a resolution of at least QUERY_PLAN_MIN_POINTS points
+        points_wanted = (before_wanted - after_wanted) > QUERY_PLAN_MIN_POINTS ? QUERY_PLAN_MIN_POINTS : before_wanted - after_wanted;
+
     time_t min_first_time_s = 0;
     time_t max_last_time_s = 0;