On Fri, Apr 13, 2018 at 6:59 AM, Michael Paquier <mich...@paquier.xyz> wrote: > On Thu, Apr 12, 2018 at 02:55:53PM -0400, Robert Haas wrote: >> I think it may actually be confusing. If you run pg_ctl reload and it >> reports that the value has changed, you'll expect it to have taken >> effect. But really, it will take effect at some later time. >
+1. I also think it is confusing and it could be difficult for end users to know when the setting is effective. > It is true that sometimes some people like to temporarily disable > full_page_writes particularly when doing some bulk load of data to > minimize the effort on WAL, and then re-enable it just after doing > the inserting this data. > > Still does it matter when the change is effective? By disabling > full_page_writes even temporarily, you accept the fact that this > instance would not be safe until the next checkpoint completes. The > instance even finishes by writing less unnecessary WAL data if the > change is only effective at the next checkpoint. Well, it is true that > this increases potential torn pages problems but the user is already > accepting that risk if a crash happens until the next checkpoint then it > exposes itself to torn pages anyway as it chose to disable > full_page_writes. > I think this means that is will be difficult for end users to predict unless they track the next checkpoint which isn't too bad, but won't be convenient either. -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
