Re: Redesigning checkpoint_segments

On 02/02/2015 03:36 PM, Robert Haas wrote:
> Second, I*think* that these settings are symmetric and, if that's
> right, then I suggest that they ought to be named symmetrically.
> Basically, I think you've got min_checkpoint_segments (the number of
> recycled segments we keep around always) and max_checkpoint_segments
> (the maximum number of segments we can have between checkpoints),
> essentially splitting the current role of checkpoint_segments in half.
> I'd go so far as to suggest we use exactly that naming. It would be
> reasonable to allow the value to be specified in MB rather than in
> 16MB units, and to specify it that way by default, but maybe a
> unit-less value should have the old interpretation since everybody's
> used to it. That would require adding GUC_UNIT_XSEG or similar, but
> that seems OK.

Works for me. However, note that "max_checkpoint_segments = 10" doesn't
mean the same as current "checkpoint_segments = 10". With
checkpoint_segments = 10 you end up with about 2x-3x as much WAL as with
max_checkpoint_segments = 10. So the "everybody's used to it" argument
doesn't hold much water.

- Heikki