diff --git a/include/neuron/connection/mqtt_client.h b/include/neuron/connection/mqtt_client.h
index dfa2f1f4..dd55f2c7 100644
--- a/include/neuron/connection/mqtt_client.h
+++ b/include/neuron/connection/mqtt_client.h
@@ -30,6 +30,11 @@ extern "C" {
 
 #include "utils/zlog.h"
 
+// number of messages cached
+#define NEU_METRIC_CACHED_MSGS_NUM "cached_msgs"
+#define NEU_METRIC_CACHED_MSGS_NUM_TYPE NEU_METRIC_TYPE_GAUAGE
+#define NEU_METRIC_CACHED_MSGS_NUM_HELP "Number of messages cached"
+
 typedef enum {
     NEU_MQTT_VERSION_V31  = 3,
     NEU_MQTT_VERSION_V311 = 4,
@@ -58,8 +63,9 @@ neu_mqtt_client_t *neu_mqtt_client_from_addr(const char *host, uint16_t port,
                                              neu_mqtt_version_e version);
 void               neu_mqtt_client_free(neu_mqtt_client_t *client);
 
-bool neu_mqtt_client_is_opened(neu_mqtt_client_t *client);
-bool neu_mqtt_client_is_connected(neu_mqtt_client_t *client);
+bool   neu_mqtt_client_is_opened(neu_mqtt_client_t *client);
+bool   neu_mqtt_client_is_connected(neu_mqtt_client_t *client);
+size_t neu_mqtt_client_get_cached_msgs_num(neu_mqtt_client_t *client);
 
 int neu_mqtt_client_set_addr(neu_mqtt_client_t *client, const char *host,
                              uint16_t port);
diff --git a/src/connection/mqtt_client.c b/src/connection/mqtt_client.c
index 834dd52f..eb4ffe57 100644
--- a/src/connection/mqtt_client.c
+++ b/src/connection/mqtt_client.c
@@ -638,7 +638,7 @@ alloc_sqlite_config(neu_mqtt_client_t *client)
     }
 
     nng_mqtt_set_sqlite_enable(cfg, true);
-    nng_mqtt_set_sqlite_flush_threshold(cfg, 256);
+    nng_mqtt_set_sqlite_flush_threshold(cfg, 1);
     nng_mqtt_set_sqlite_max_rows(cfg, 256);
     nng_mqtt_set_sqlite_db_dir(cfg, "persistence/");
     nng_mqtt_sqlite_db_init(cfg, db, client->version);
@@ -710,6 +710,15 @@ bool neu_mqtt_client_is_connected(neu_mqtt_client_t *client)
     return client->connected;
 }
 
+size_t neu_mqtt_client_get_cached_msgs_num(neu_mqtt_client_t *client)
+{
+    if (NULL == client->sqlite_cfg) {
+        return 0;
+    }
+
+    return nng_mqtt_sqlite_db_get_cached_size(client->sqlite_cfg);
+}
+
 int neu_mqtt_client_set_addr(neu_mqtt_client_t *client, const char *host,
                              uint16_t port)
 {