Re: [HACKERS] increasing the default WAL segment size

On Tue, Jan 3, 2017 at 6:41 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> On 2 January 2017 at 21:23, Jim Nasby <Jim.Nasby@bluetreble.com> wrote:
>
>> It's not clear from the thread that there is consensus that this feature is desired. In particular, the performance
aspectsof changing segment size from a C constant to a variable are in question. Someone with access to large hardware
shouldtest that. Andres[1] and Robert[2] did suggest that the option could be changed to a bitshift, which IMHO would
alsosolve some sanity-checking issues. 
>
> Overall, Robert has made a good case. The only discussion now is about
> the knock-on effects it causes.
>
> One concern that has only barely been discussed is the effect of
> zero-ing new WAL files. That is a linear effect and will adversely
> effect performance as WAL segment size increases.
>

Sorry, but I am not able to understand why this is a problem?  The
bigger the size of WAL segment, lesser the number of files.  So IIUC,
then it can only impact if zero-ing two 16MB files is cheaper than
zero-ing one 32MB file.  Is that your theory or you have something
else in mind?


--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com