Db::stat with DB_FAST_STAT seems to be unreliable

Question

I need to obtain record counts for databases within a large physical file and callingDb::stat with DB_FAST_STAT seems to return zero sometimes, while calling Db::stat without DB_FAST_STAT returns the proper value, at the expense of a full table scan, which in my case spans minutes. How can I ensure that Db::stat(DB_FAST_STAT) always returns actual number of records?
Thanks,
Andre

Answer 1

Oh, I know why you are doing this, but it doesn't help database performance when one has to wait for minutes and use up more than a gig of RAM to get a count. To make things more complicated, Db::put does not indicate whether a record was updated or inserted, which would facilitate out-of-database count maintenance. This leaves BDB users with a single option - look up a key first and then insert a record and bump up an app-specific counter. When you consider the expense of doing that and the fact that a fairly complex algorithm is needed to make look-up/insert atomic on a per-key basis, a single mutex lock protecting a single increment/decrement operation doesn't seem that bad, especially when there are few threads accessing the database.
Any chance you could make this option configurable and let users choose whether to take maintain a per-database record count and take a small hit on every lookup/update instead of using an unreliable record count?
Also, if you would consider changing Db::put to return an indicator of whether the record existed or not, that would be awesome.
Andre