Alexander V. Klepikov wrote:
>... If connection to DB fails, PQfinish(pg_sock->conn) is called, which frees 
> pg_sock->conn - need to do this is described in libpq docs. So even in case 
> of unsuccessefull connection we have good "database handle" sqlsocket->conn, 
> which should not be NULL.

  If pg_sock->conn is freed, that pointer MUST be set to NULL.

> According to this, I can make a conclusion that when database handle is 
> checked for connectivity (in rlm_sql module), sqlsocket->state should be 
> used.

  No.  sqlsocket->state is redundant.  If the "conn" handle exists, it
MUST be a valid connection handle.  If it's not valid, it's NULL, and
therefore the socket is disconnected.

> In theory, sqlsocket->state can equals to sockconnected when actually 
> it is disconnected.

  That's a bug.  It's wrong and MUST be fixed.

> It seemes to me, actually this can happen very rarely. 
> May be, state of connection should be checked before running every SQL query 
> to minimize risk of operation on disconnected DB, but I believe it's not 
> necessary yet. Besides, it will require to modify all sql drivers.

  Then we modify all of the SQL drivers.

  Alan DeKok.
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