Re: WALWriteLock contention

On Fri, May 15, 2015 at 1:09 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> WALWriteLock contention is measurable on some workloads. In studying
>> the problem briefly, a couple of questions emerged:
>
>> 1. Doesn't it suck to rewrite an entire 8kB block every time, instead
>> of only the new bytes (and maybe a few bytes following that to spoil
>> any old data that might be there)?
>
> It does, but it's not clear how to avoid torn-write conditions without
> that.

Can you elaborate? I don't understand how repeatedly overwriting the
same bytes with themselves accomplishes anything at all.

--
Robert Haas
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