docs: Add documentation of metrics to README

README.md

@@ -125,6 +125,19 @@ Some of the connection pool configurations can be adjusted dynamically. Each con
 - max_idle_closed - The total number of connections closed due to max_idle.
 - max_lifetime_closed - The total number of connections closed due to max_lifetime.
 
+## Metrics
+
+- Counters
+    - OPENED_TOTAL - Total number of Pool Connections opened
+    - CLOSED_TOTAL - Total number of Pool Connections closed
+- Gauges
+    - OPEN_CONNECTIONS - Number of currently open Pool Connections
+    - ACTIVE_CONNECTIONS - Number of currently busy Pool Connections (executing a database query)"
+    - IDLE_CONNECTIONS - Number of currently unused Pool Connections (waiting for the next pool query to run)
+    - WAIT_COUNT - Number of queries currently waiting for a connection
+- Histograms
+    - WAIT_DURATION - Histogram of the wait time of all queries in ms
+
 ## Compatibility
 
 Because tokio is not compatible with other runtimes, such as async-std. So a database driver written with tokio cannot run in the async-std runtime. For example, you can't use redis-rs in tide because it uses tokio, so the connection pool which bases on redis-res can't be used in tide either.

src/metrics_utils.rs

@@ -1,13 +1,17 @@
 use metrics::{describe_counter, describe_gauge, describe_histogram};
 
+// counters
 pub const OPENED_TOTAL: &str = "mobc_pool_connections_opened_total";
 pub const CLOSED_TOTAL: &str = "mobc_pool_connections_closed_total";
-pub const OPEN_CONNECTIONS: &str = "mobc_pool_connections_open";
 
+// gauges
+pub const OPEN_CONNECTIONS: &str = "mobc_pool_connections_open";
 pub const ACTIVE_CONNECTIONS: &str = "mobc_pool_connections_busy";
 pub const IDLE_CONNECTIONS: &str = "mobc_pool_connections_idle";
-pub const WAIT_COUNT: &str = "mobc_client_queries_wait";
-pub const WAIT_DURATION: &str = "mobc_client_queries_wait_histogram_ms";
+pub const WAIT_COUNT: &str = "mobc_queries_wait";
+
+// histogram
+pub const WAIT_DURATION: &str = "mobc_queries_wait_histogram_ms";
 
 pub fn describe_metrics() {
     describe_counter!(OPENED_TOTAL, "Total number of Pool Connections opened");