On Tue, Dec 30, 2014 at 12:35 AM, Guillaume Lelarge <guilla...@lelarge.info> wrote:
> Sorry for my very late answer. It's been a tough month. > > 2014-11-27 0:00 GMT+01:00 Bruce Momjian <br...@momjian.us>: > >> 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: >> >> max(2 * checkpoint_segments, wal_keep_segments) + 2 * >> checkpoint_segments + 2 >> >> > 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. Cheers, Jeff
