[Pgsql-ayuda] Monitoreo con pg_stat_activity

Hola a todos.
Necesito monitorear las conexiones existentes en determinado servidor. Por
lo que estuve leyendo en esta lista, estoy utilizando lo siguiente:

dbtest=> select * from pg_stat_activity order by procpid;

datid | datname | procpid | usesysid | usename | current_query
-----------+------------------+---------+----------+---------+--------------
536047581 | test_database1 | 332 | 100 | pictage |
520023417 | test_database2 | 335 | 100 | pictage |
520023417 | test_database2 | 338 | 100 | pictage |
553919440 | test_database3 | 428 | 100 | pictage |
520023417 | test_database2 | 431 | 100 | pictage |
536047781 | test_database4 | 478 | 100 | pictage |
536047581 | test_database1 | 481 | 100 | pictage |
536047581 | test_database1 | 616 | 100 | pictage |
536047581 | test_database1 | 751 | 100 | pictage |
536047581 | test_database1 | 771 | 100 | pictage |
536047781 | test_database4 | 805 | 100 | pictage |
536047781 | test_database4 | 818 | 100 | pictage |
553919404 | test_database5 | 828 | 100 | pictage |
520023417 | test_database2 | 835 | 100 | pictage |
520023417 | test_database2 | 908 | 100 | pictage |
553919433 | stage_database6 | 910 | 100 | pictage |
520023417 | test_database2 | 951 | 100 | pictage |
553919440 | test_database3 | 954 | 100 | pictage |
553919440 | test_database3 | 955 | 100 | pictage |
536047781 | test_database4 | 961 | 100 | pictage |
536047581 | test_database1 | 966 | 100 | pictage |
520023417 | test_database2 | 972 | 100 | pictage |
553919440 | test_database3 | 973 | 100 | pictage |
553919404 | test_database5 | 981 | 100 | pictage |
553919440 | test_database3 | 1015 | 100 | pictage |
553919440 | test_database3 | 1182 | 100 | pictage |
553919440 | test_database3 | 1183 | 100 | pictage |
536047581 | test_database1 | 1195 | 100 | pictage |
553919440 | test_database3 | 1196 | 100 | pictage |
536047781 | test_database4 | 1206 | 100 | pictage |
520023417 | test_database2 | 1207 | 100 | pictage |
536047581 | test_database1 | 1208 | 100 | pictage |
520023417 | test_database2 | 1224 | 100 | pictage |
520023417 | test_database2 | 1225 | 100 | pictage |
670615972 | test_database7 | 31872 | 100 | pictage |
536047781 | test_database4 | 32183 | 100 | pictage |
536047781 | test_database4 | 32491 | 100 | pictage |

Preguntas: por qu obtengo el mismo datid para distintas conexiones? Hay
alguna documentacin buena acerca de esta tabla para entender claramente
cada columna?

Gracias.

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