Re: [EXTERNAL] Re: WIP: WAL prefetch (another approach) - Mailing list pgsql-hackers

From Andres Freund
Subject Re: [EXTERNAL] Re: WIP: WAL prefetch (another approach)
Date
Msg-id 6B918AFB-88D6-4687-8B4A-34C472E48BF4@anarazel.de
Whole thread Raw
In response to Re: [EXTERNAL] Re: WIP: WAL prefetch (another approach)  (Stephen Frost <sfrost@snowman.net>)
Responses Re: [EXTERNAL] Re: WIP: WAL prefetch (another approach)  (Stephen Frost <sfrost@snowman.net>)
List pgsql-hackers
Hi,

On August 27, 2020 11:26:42 AM PDT, Stephen Frost <sfrost@snowman.net> wrote:
>Is WAL FPW compression enabled..?  I'm trying to figure out how, given
>what's been shared here, that replaying 25GB of WAL is being helped out
>by 2.5x thanks to prefetch in the SSD case.  That prefetch is hurting
>in
>the HDD case entirely makes sense to me- we're spending time reading
>pages from the HDD, which is entirely pointless work given that we're
>just going to write over those pages entirely with FPWs.

Hm? At least earlier versions didn't do prefetching for records with an fpw, and only for subsequent records affecting
thesame or if not in s_b anymore. 

Andres
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.



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