On Fri, Jul 6, 2018 at 8:57 PM, Andres Freund <andres@anarazel.de> wrote:
On 2018-07-06 14:49:53 -0400, Robert Haas wrote: > I think we also have to ask ourselves in general whether snapshots of > this data are worth what they cost. I don't think anyone would doubt > that a consistent snapshot of the data is better than an inconsistent > view of the data if the costs were equal. However, if we can avoid a > huge amount of memory usage and complexity on large systems with > hundreds of backends by ditching the snapshot requirement, then we > should ask ourselves how important we think the snapshot behavior > really is.
Indeed. I don't think it's worthwhile major additional memory or code complexity in this situation. The likelihood of benefitting from more / better stats seems far higher than a more accurate view of the stats - which aren't particularly accurate themselves. They don't even survive crashes right now, so I don't think the current accuracy is very high.
Definitely agreed.
*If* we can provide the snapshots view of them without too much overhead I think it's worth looking into that while *also* proviiding a lower overhead interface for those that don't care about it.
If it ends up that keeping the snapshots become too much overhead in either in performance or code-maintenance, then I agree can probably drop that. But we should at least properly investigate the cost.