pg_stat_activity各字段的含义如下：
datid: Database OID
datname: Database name
procpid:Process ID
usesysid: OID of the database user
usename:the username that associates to the usesysid above
current_query: The actual query that this connection is currently running
waiting: The actual status of the query if it is waiting or not. Typically you will see f or t in this field.
xact_start:The time at which the transaction started to run which could
be different than the query_start but should always have occurred before
the query_start time.
query_start: The time at which the query started to run. This can be
useful to determine if a query has been running for a long time.
backend_start:The time at which the database was accessed by the client.
If using persistent connections the backend_start time could be hours,
days, etc. older than the xact_start and query_start times.
client_addr:The IP address of the connection which typically will be
localhost or 127.0.0.1 unless you have a remote user or application
connecting directly to the database server. With a lot of web
applications the application and database are on the same server so even
though the user connecting to the web application is remote the
connection here will show local because the application is accessing the
database not the user directly.
client_port: The port the client user or application is using to connect
to the database. Again this is typically going to be a local port since
the actual user might be accessing a web application which is then
accessing the database.