delete taking long time

HI,

I have the following table:

Table "public.connection"

Column | Type | Modifiers

-------------------+--------------------------------+-----------

uid | character varying(18) | not null

ts | timestamp(6) without time zone | not null

host_origin | inet | not null

port_origin | integer | not null

host_destination | inet | not null

port_destination | integer | not null

protocol | character varying(12) |

service | character varying(12) |

duration | interval second(6) |

origin_bytes | bigint |

response_bytes | bigint |

connection_state | character varying(8) |

local_origin | boolean |

local_response | boolean |

missed_bytes | bigint |

history | text |

origin_packets | bigint |

origin_ip_bytes | bigint |

response_packets | bigint |

response_ip_bytes | bigint |

Indexes:

"connection_pkey" PRIMARY KEY, btree (uid)

Foreign-key constraints:

"connection_protocol_fkey" FOREIGN KEY (protocol) REFERENCES
protocol(name)

"connection_service_fkey" FOREIGN KEY (service) REFERENCES service(name)

Referenced by:

TABLE "dns" CONSTRAINT "dns_uid_fkey" FOREIGN KEY (uid) REFERENCES
connection(uid)

TABLE "files" CONSTRAINT "files_uid_fkey" FOREIGN KEY (uid) REFERENCES
connection(uid)

TABLE "http" CONSTRAINT "http_uid_fkey" FOREIGN KEY (uid) REFERENCES
connection(uid)

TABLE "notice" CONSTRAINT "notice_uid_fkey" FOREIGN KEY (uid)
REFERENCES connection(uid)

TABLE "snmp" CONSTRAINT "snmp_uid_fkey" FOREIGN KEY (uid) REFERENCES
connection(uid)

TABLE "ssl" CONSTRAINT "ssl_uid_fkey" FOREIGN KEY (uid) REFERENCES
connection(uid)

TABLE "weird" CONSTRAINT "weird_uid_fkey" FOREIGN KEY (uid) REFERENCES
connection(uid)

I am trying to delete the connections with date 2016-03-10 by using the
following:

delete from connection where uid in (select uid from connection where ts >
'2016-03-10 00:30:00');

There are around 800.000 records matching this rule, and seems to be taking
an awful lot of time - 4 hours and counting. What could be the reason for
such a performance hit and how could I optimise this for future cases?

Regards.