BIG-IP : under what conditions does LB_SELECTED event fire ?

F5 BIG-IP Virtual Edition v11.4.1 (Build 635.0) LTM on ESXi

Under what conditions does the

LB_SELECTED

event fire ?

If within an iRule's

HTTP_REQUEST

event-processing-block the pool is explicitly set :

when HTTP_REQUEST {
  pool "my-pool-01"
}

it appears this will trigger the

LB_SELECTED

event ( following execution of all

HTTP_REQUEST

event-processing-blocks ).

But what about the case where the pool is not explicitly set within any iRule , but the virtual-server routes traffic to default pool ?

In this scenario , will the

LB_SELECTED

event still fire ?

Also, do

LB_SELECTED

event-processing-blocks fire only after all

HTTP_REQUEST

event-processing-blocks have completed ? So for a stack of 2 iRules, if I have

HTTP_REQUEST

blocks in iRules 1 & 2 , will an

LB_SELECTED

block in iRule 1 begin execution only after the

HTTP_REQUEST

block in iRule 2 has completed execution ?

Another question : my event logs seem to indicate that for a client's initial request upon selecting a pool member the

LB_SELECTED

event will fire, but not re-fire for subsequent requests by same client to the same back-end server. Is this due to keep-alives establishing a session where selected pool node is maintained for session duration ? Or why else would

LB_SELECTED

event no longer fire ?