Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)

On Tue, Mar 21, 2017 at 10:21 AM, Alvaro Herrera
<alvherre@2ndquadrant.com> wrote:
> Robert Haas wrote:
>> On Tue, Mar 21, 2017 at 10:01 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>
>> > Sure, we can try that.  I think we need to try it with
>> > synchronous_commit = off, otherwise, WAL writes completely overshadows
>> > everything.
>>
>> synchronous_commit = off is a much more realistic scenario than fsync = off.
>
> Sure, synchronous_commit=off is a reasonable case.  But I say if we lose
> a few % on the case where you update only the first indexed of a large
> number of very wide columns all indexed, and this is only noticeable if
> you don't write WAL and only if you update all the rows in the table,
> then I don't see much reason for concern.

If the WAL writing hides the loss, then I agree that's not a big
concern.  But if the loss is still visible even when WAL is written,
then I'm not so sure.

-- 
Robert Haas
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