Re: [HACKERS] PG 10 release notes

On Tue, Apr 25, 2017 at 01:37:13PM -0300, Claudio Freire wrote:
> > I think it has been pretty common to accumulate a lot of such changes
> > into generic entries like, say, "speedups for hash joins".  More detail
> > than that simply isn't useful to end users; and as a rule, our release
> > notes are too long anyway.
> 
> In that spirit, the truncation speedups it seems are missing:
> 
> Might be summarized simply as:
> 
> Vacuum truncation has been sped up for rotating media, sometimes
> considerably (up to five times in certain configurations).
> 
> Full commit, for reference:
> 
> commit 7e26e02eec90370dd222f35f00042f8188488ac4
> Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
> Date:   Mon Jan 23 12:55:18 2017 -0300
> 
>     Prefetch blocks during lazy vacuum's truncation scan
> 
>     Vacuum truncation scan can be sped up on rotating media by prefetching
>     blocks in forward direction.  That makes the blocks already present in
>     memory by the time they are needed, while also letting OS read-ahead
>     kick in.
> 
>     The truncate scan has been measured to be five times faster than without
>     this patch (that was on a slow disk, but it shouldn't hurt on fast
>     disks.)
> 
>     Author: Álvaro Herrera, loosely based on a submission by Claudio Freire
>     Discussion:
> https://postgr.es/m/CAGTBQpa6NFGO_6g_y_7zQx8L9GcHDSQKYdo1tGuh791z6PYgEg@mail.gmail.com

I don't think this warrants inclusion in the release notes for reasons
already discussed.  The vacuum truncation operation is a rare one and
an implementation detail.

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

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