Carefully removing unwanted indexes
Carefully removing? Do you mean pressing Enter gently after typing DROP INDEX? Err, no!
The reasoning is that it takes a long time to build an index and a short time to drop it.
What we want is a way of removing an index so that if we discover that removing it was a mistake, we can put the index back again quickly.
Getting ready
The following query will list all invalid indexes, if any:
SELECT ir.relname AS indexname , it.relname AS tablename , n.nspname AS schemaname FROM pg_index i JOIN pg_class ir ON ir.oid = i.indexrelid JOIN pg_class it ON it.oid = i.indrelid JOIN pg_namespace n ON n.oid = it.relnamespace WHERE NOT i.indisvalid;
Take note of these indexes so that you can tell whether a given index is invalid later because we marked it as invalid during this recipe, in which case it can safely be marked as valid, or because it was already invalid for other reasons.