There aren't a general solution. If you realy need the exact count of
tuples than you can play with a TRIGGER and increase/decrease the
tuple-count for this table in an extra table.
Of course, this means accepting the cost of obtaining update locks on the count table.
The original poster should understand that they can either get a fast estimated count, or they can get a slow accurate count (either slow in terms of select using count(*) or slow in terms of updates using triggers and locking).
Other systems have their own issues. An index scan may be faster than a table scan for databases that can accurately determine counts using only the index, but it's still a relatively slow operation, and people don't normally need an accurate count for records in the range of 100,000+? :-)
Cheers,
mark
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Mark Mielke <mark@mielke.cc>