diff --git a/Dockerfile.dev b/Dockerfile.dev
deleted file mode 100644
index 58884e9..0000000
--- a/Dockerfile.dev
+++ /dev/null
@@ -1,12 +0,0 @@
-FROM ubuntu:16.04
-
-RUN apt update && \
-	apt install -y wget vim git gcc httpie dnsutils
-
-RUN wget https://dl.google.com/go/go1.12.4.linux-amd64.tar.gz && \
-	tar -C /usr/local -xzf go1.12.4.linux-amd64.tar.gz && \
-	rm go1.12.4.linux-amd64.tar.gz
-
-ENV PATH $PATH:/usr/local/go/bin
-
-RUN go get github.com/Shopify/sarama
\ No newline at end of file
diff --git a/src/resource_pool.go b/src/resource_pool.go
index dccb8eb..f1181af 100644
--- a/src/resource_pool.go
+++ b/src/resource_pool.go
@@ -15,6 +15,7 @@ type ResourcePool struct {
 func (pool *ResourcePool) start() {
 	go func() {
 		/* waiting for data */
+		pool.history = []PoolStatus{}
 		time.Sleep(time.Second * 30)
 		for {
 			summary := PoolStatus{}
@@ -58,7 +59,7 @@ func (pool *ResourcePool) start() {
 			pool.history = append(pool.history, summary)
 
 			if len(pool.history) > 60 {
-				pool.history = pool.history[0:60]
+				pool.history = pool.history[len(pool.history)-60:]
 			}
 			time.Sleep(time.Second * 60)
 		}