Re: Redesigning checkpoint_segments

On 01/03/2015 12:28 AM, Josh Berkus wrote:
> On 01/02/2015 01:57 AM, Heikki Linnakangas wrote:
>> wal_keep_segments does not affect the calculation of CheckPointSegments.
>> If you set wal_keep_segments high enough, checkpoint_wal_size will be
>> exceeded. The other alternative would be to force a checkpoint earlier,
>> i.e. lower CheckPointSegments, so that checkpoint_wal_size would be
>> honored. However, if you set wal_keep_segments high enough, higher than
>> checkpoint_wal_size, it's impossible to honor checkpoint_wal_size no
>> matter how frequently you checkpoint.
>
> So you're saying that wal_keep_segments is part of the max_wal_size
> total, NOT in addition to it?

Not sure what you mean. wal_keep_segments is an extra control that can 
prevent WAL segments from being recycled. It has the same effect as 
archive_command failing for N most recent segments, if that helps.

> Just asking for clarification, here.  I think that's a fine idea, I just
> want to make sure I understood you.  The importance of wal_keep_segments
> will be fading as more people use replication slots.

Yeah.

- Heikki