James,
> if I had three tables for a many to many relationship say A, B, AND C
> B being the lookup. B being a huge 50k rows plus column and made just two
forigen keys(b.a_id,b.c_id).
> is it best to create two non-unique indexes or one unique index on both
fields?
That depends on whether all three tables are usually queried toghether. If
yes, then a 2-column index is probably better. If not, use single-column
indexes. If you want more specific advice, post your table structures.
> I also attempted creating an index on a table i have called person on
person_id and
> ran
> Explain
> select person_id from person where person_id < n
>
> but saw no results of my created index being used - am i doing something
incorrectly
Not a surprise. If your the planner expects person_id < n to return a
significant portion of the table, a table scan is faster than an index scan.
> Pps
> When indexing if searching tables is more important than concurrency - which
type of index is best?
You want to use a B-tree index for anything other than statistical and/or
geometic data. You are unlikely to need any other kind of index.
--
-Josh Berkus
Aglio Database Solutions
San Francisco
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