diff --git a/src/query/inc/tdigest.h b/src/query/inc/tdigest.h
index 81bbdb0226ca437d45a50d38250543d4e7a9d5c4..758eba486496930bb6d6a967186a45e638900fea 100644
--- a/src/query/inc/tdigest.h
+++ b/src/query/inc/tdigest.h
@@ -26,11 +26,11 @@
 #define M_PI        3.14159265358979323846264338327950288   /* pi             */
 #endif
 
-#define ADDITION_CENTROID_NUM 100
+#define ADDITION_CENTROID_NUM 2
 #define COMPRESSION 400
 #define GET_CENTROID(compression)  (ceil(compression * M_PI / 2) + 1 + ADDITION_CENTROID_NUM)
 #define GET_THRESHOLD(compression) (7.5 + 0.37 * compression - 2e-4 * pow(compression, 2))
-#define TDIGEST_SIZE(compression)  (sizeof(TDigest) + sizeof(SPt)*GET_THRESHOLD(compression))
+#define TDIGEST_SIZE(compression)  (sizeof(TDigest) + sizeof(SCentroid)*GET_CENTROID(compression) + sizeof(SPt)*GET_THRESHOLD(compression))
 
 typedef struct SCentroid {
     double mean;
diff --git a/src/query/src/tdigest.c b/src/query/src/tdigest.c
index 3028b8daa9a48046dd2abd7704aa87c592ac1241..eb78e8aceebb13b83dd7fe60c9a704f418860797 100644
--- a/src/query/src/tdigest.c
+++ b/src/query/src/tdigest.c
@@ -29,7 +29,7 @@
 #include "tdigest.h"
 
 #define INTERPOLATE(x, x0, x1) (((x) - (x0)) / ((x1) - (x0)))
-#define INTEGRATED_LOCATION(compression, q) ((compression) * (asin(2 * (q) - 1) + M_PI / 2) / M_PI)
+#define INTEGRATED_LOCATION(compression, q) ((compression) * (asin(2 * (double)(q) - 1)/M_PI + (double)1/2))
 #define FLOAT_EQ(f1, f2) (fabs((f1) - (f2)) <= FLT_EPSILON)
 
 typedef struct SMergeArgs {
@@ -78,26 +78,28 @@ static void mergeCentroid(SMergeArgs *args, SCentroid *merge) {
     SCentroid *c = &args->centroids[args->idx];
 
     args->weight_so_far += merge->weight;
-    k2 = INTEGRATED_LOCATION(args->t->compression,
-            args->weight_so_far / args->t->total_weight);
-
-    if (k2 - args->k1 > 1 && c->weight > 0) {
-        if(args->idx + 1 < args->t->size) { // check avoid overflow
-            args->idx++; 
-        } else {
-          assert(0);
+    k2 = INTEGRATED_LOCATION(args->t->size,
+            args->weight_so_far / (args->t->total_weight + merge->weight));
+    //idx++
+    if(k2 - args->k1 > 1 && c->weight > 0) {
+        if(args->idx + 1 < args->t->size
+         && merge->mean != args->centroids[args->idx].mean) {
+             args->idx++;     
         }
-        args->k1 = INTEGRATED_LOCATION(args->t->compression,
-                (args->weight_so_far - merge->weight) / args->t->total_weight);
+        args->k1 = k2;
     }
 
     c = &args->centroids[args->idx];
-    c->weight += merge->weight;
-    c->mean += (merge->mean - c->mean) * merge->weight / c->weight;
-
-    if (merge->weight > 0) {
-        args->min = MIN(merge->mean, args->min);
-        args->max = MAX(merge->mean, args->max);
+    if(c->mean == merge->mean) {
+        c->weight += merge->weight;
+    } else {
+        c->weight += merge->weight;
+        c->mean += (merge->mean - c->mean) * merge->weight / c->weight;
+
+        if (merge->weight > 0) {
+            args->min = MIN(merge->mean, args->min);
+            args->max = MAX(merge->mean, args->max);
+        }
     }
 }
 
@@ -163,10 +165,13 @@ void tdigestAdd(TDigest* t, double x, int64_t w) {
         return;
 
     int32_t i = t->num_buffered_pts;
-    t->buffered_pts[i].value  = x;
-    t->buffered_pts[i].weight = w;
-    t->num_buffered_pts++;
-    t->total_weight += w;
+    if(i > 0 && t->buffered_pts[i-1].value == x ) {
+        t->buffered_pts[i].weight = w;
+    } else {
+        t->buffered_pts[i].value  = x;
+        t->buffered_pts[i].weight = w;
+        t->num_buffered_pts++;        
+    }
 
     if (t->num_buffered_pts >= t->threshold)
         tdigestCompress(t);