[firebird-support] Question about few Firebird details

[liviuslivius liviusliv...@poczta.onet.pl [firebird-support]]

Hi,
 
https://ib-aid.com/en/articles/45-ways-to-speed-up-firebird-database/
i have few questions:
44. Use NO_AUTO_UNDO - what happend when i do rollback? I do not understand 
what really do this option..
30. Use derived tables to optimize SELECT with ORDER BY/GROUP BY - 
SELECT T.FIELD_KEY, T.FIELD1, T.FIELD2, ... T.FIELD_N FROM (SELECT FIELD_KEY 
FROM T ORDER BY FIELD2) T2 JOIN T ON T.FIELD_KEY = T2.FIELD_KEY
why this can be faster then?
SELECT FIELD_KEY, FIELD1, FIELD2, ... FIELD_N FROM T ORDER BY FIELD2
Firebird sort whole resultset of "sorted key - Field2" or do different work?
I see in FB3 plan sort width and it looks like not true but?
 
regards,
Karol Bieniaszewski