Full table scan on insert/update

[bjne]

I am seeing a full table scan on insert/update. Strange thing this does not happen on the first few
commands after connection.. Is this known? What is causing the cursor-dance?

[RhodiumToad]

This is caused by ktGetForeignPaths returning the same cost for the path regardless of whether there is a usable key qual or not. Thus, the plan cache can't tell that the generic (key = Param) qual is far more expensive than the (key = Const) qual that results from a custom plan. The plan cache in 9.2+ always uses custom plans for the first few calls, to get a cost baseline, then compares the generic plan cost to the average custom plan cost.

To fix: ktGetForeignPaths should compute a lower cost if a usable key qual is present.