Hi Menashè,

1. In which cases the "applying index" phrase should I see in the query plan?

There is no simple answer to that question. The query optimizer tries to select a query plan that is evaluated faster than others. The following query may illustrate this:

for $p in db:open('db')//person where $p/country = 'Italy' and $p/sex = 'female' return $p

There are at least three ways how this query could e.g. be rewritten:

db:text('db', 'Italy')/parent::country/ parent:person/person[sex = 'female']

db:text('db', 'female')/parent:sex/ parent::person[city = 'Catania']

(db:text('db', 'Italy')/parent::country, db:text('db', 'female')/parent::sex)/parent::country

In most cases, only one index access will be created will be created for queries of that pattern. The optimizer also checks the number of index entries given for a particular keyword. In the given case, the query would most probably rewritten to the first query plan.

If you have a query with just six conditions, there are more than 50 different ways how your final query plan could look like.

2. Only once a value which is mentioned in the query is found in the index, in

case of "=" condition?

In most cases, exact queries are preferred, because they are usually more selective than other queries.

3. Always, in case of "<" or "<" condition, assuming the specific

text/attribute has been indexed?

Because none of our index structures is particularly suited for range queries, such index-driven requests may be slower than sequential scans. Maybe you remember my last mail: Have you already tried to store latitudes and longitudes in a fixed-size string representation?

4. Everything I see as a reply to index:facets is indexed, right?

I'm not sure what you mean by that?