PostgreSQL 8.2beta2 Documentation | ||||
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GIN doesn't support full index scans due to their extremely inefficiency: because there are often many keys per value, each heap pointer will returned several times.
When extractQuery returns zero keys, GIN will emit a error: for different opclasses and strategies the semantic meaning of a void query may be different (for example, any array contains the void array, but they don't overlap the void array), and GIN can't suggest reasonable answer.
GIN searches keys only by equality matching. This may be improved in future.