On Mon, Nov 3, 2014 at 12:39:26PM -0800, Jeff Janes wrote: > It looked to me that the formula, when descending from a previously stressed > state, would be: > > greatest(1 + checkpoint_completion_target) * checkpoint_segments, > wal_keep_segments) + 1 + > 2 * checkpoint_segments + 1
I don't think we can assume checkpoint_completion_target is at all reliable enough to base a maximum calculation on, assuming anything above the maximum is cause of concern and something to inform the admins about.
Assuming checkpoint_completion_target is 1 for maximum purposes, how about:
Seems something I could agree on. At least, it makes sense, and it works for my customers. Although I'm wondering why "+ 2", and not "+ 1". It seems Jeff and you agree on this, so I may have misunderstood something.
From hazy memory, one +1 comes from the currently active WAL file, which exists but is not counted towards either wal_keep_segments nor towards recycled files. And the other +1 comes from the formula for how many recycled files to retain, which explicitly has a +1 in it.