Re: Erroneous cost estimation for nested loop join

We guessed the cause of this error would be in the cost model of Postgres, and investigated the source code of optimizer, and we found the cause of this problem. It was in the index cost estimation process. On scanning inner table, if loop count is greater than 1, its I/O cost is counted as random access. In the case of Query2, in one loop (i.e. one inner table scan) , much data is read sequentially with clustered index, so it seems to be wrong that optimizer thinks its I/O workload is random access.