Query Execution Speed - Sesame Native Store

Hello, all!
I have some questions regarding 3 aspects of Sesame influencing Query
Execution Speed.

1) Indexes

I am using Sesame 2.7 Native Store with the indexes
spoc,sopc,psoc,posc,opsc,ospc.
I am not using Contexts so I just used all combinations of indexes for
(s,p,o) because, according to Sesame User
Guide<http://www.openrdf.org/doc/sesame2/users/ch07.html#section-native-store-config>,
the more indexes the faster the query execution will be. I care much more
about query speed than loading time and space on disk.

Question: Is my approach right? Using all those indexes together will
really speed up my queries? Or may it somehow slow down depending on
something that I am not taking into consideration?

2) Contexts, named graphs.

As I understood, contexts within my Sesame RDF repository work more as an
"identifier" of a subset of the dataset.  I am not using contexts at all so
I just ignore the "c" part of the quads and I only include triples.

Should I also think about modeling my problem considering contexts? Hence,
include more indexes, maybe all combinations of the four letters (s,p,o,c)?
Will it speed up my queries if I include contexts in my statements?

3) Loading interruption

While loading data, my application may be interrupted (because of power
outage or connection loss, for example). May that cause any serious damage
to the repository, corrupting the indexes hence slowing down my queries?


PS: I have around 1M triples. I just dropped my whole database and started
building a new one all over to discard any problems related to database
corruptions and size. (Before dropping I had over 70M triples and the
queries were as slow as now with 1M triples).


Please, let me know if you have any clue regarding any of those questions.

Thank you very much.
Renan

-- 
Renan