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.
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. -- Michael
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