diff --git a/core/od_stat.h b/core/od_stat.h
new file mode 100644
index 00000000..5aac5a94
--- /dev/null
+++ b/core/od_stat.h
@@ -0,0 +1,51 @@
+#ifndef OD_STAT_H_
+#define OD_STAT_H_
+
+/*
+ * odissey.
+ *
+ * PostgreSQL connection pooler and request router.
+*/
+
+typedef struct od_stat_t od_stat_t;
+
+#define OD_STAT_MAX 8
+
+struct od_stat_t {
+	int pos;
+	uint32_t stat[OD_STAT_MAX];
+};
+
+static inline void
+od_stat_init(od_stat_t *stat)
+{
+	stat->pos = 0;
+	memset(stat->stat, 0, sizeof(stat->stat));
+}
+
+static inline void
+od_stat_tick(od_stat_t *stat)
+{
+	stat->pos = (stat->pos + 1) % OD_STAT_MAX;
+	stat->stat[stat->pos] = 0;
+}
+
+static inline void
+od_stat_add(od_stat_t *stat, uint32_t value)
+{
+	stat->stat[stat->pos] += value;
+}
+
+static inline float
+od_stat_avg(od_stat_t *stat)
+{
+	float sum = 0;
+	int i = 0;
+	while (i < OD_STAT_MAX) {
+		sum += stat->stat[i];
+		i++;
+	}
+	return sum / (float)OD_STAT_MAX;
+}
+
+#endif