This section describes the types, names, and meanings of ApacheHttpClient connection pool metrics collected by APM.

**Table 1** ApacheHttpClient connection pool metrics
Category	Metric	Name	Description	Unit	Data Type	Default Aggregation Mode
Connection pool (connectionPool: statistics about ApacheHttpclient connections in different states)	poolId	poolId	ApacheHttpclient connection pool ID	-	ENUM	LAST
	available	available	Number of idle connections in the connection pool	-	INT	SUM
	leased	leased	Number of connections occupied	-	INT	SUM
	max	max	Maximum number of connections in the connection pool	-	INT	MAX
	pending	pending	Number of pending connections in the connection pool	-	INT	SUM
Connection pool route (collectionPoolRoute: APM counts connection statistics by pool route.)	poolId	poolId	ApacheHttpClient connection pool ID	-	ENUM	LAST
	route	route	Routing information of the connection pool	-	ENUM	LAST
	available	available	Number of idle connections in the connection pool	-	INT	SUM
	leased	leased	Number of connections occupied	-	INT	SUM
	max	max	Maximum number of connections in the connection pool	-	INT	MAX
	pending	pending	Number of pending connections in the connection pool	-	INT	SUM

ApacheHttpClient Connection Pool