Re: Spread checkpoint sync

Greg Smith wrote:
> One of the components to the write queue is some notion that writes that 
> have been waiting longest should eventually be flushed out.  Linux has 
> this number called dirty_expire_centiseconds which suggests it enforces 
> just that, set to a default of 30 seconds.  This is why some 5-minute 
> interval checkpoints with default parameters, effectively spreading the 
> checkpoint over 2.5 minutes, can work under the current design.  
> Anything you wrote at T+0 to T+2:00 *should* have been written out 
> already when you reach T+2:30 and sync.  Unfortunately, when the system 
> gets busy, there is this "congestion control" logic that basically 
> throws out any guarantee of writes starting shortly after the expiration 
> time.

Should we be writing until 2:30 then sleep 30 seconds and fsync at 3:00?

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
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