Re: [HACKERS] increasing the default WAL segment size - Mailing list pgsql-hackers

From David Steele
Subject Re: [HACKERS] increasing the default WAL segment size
Date
Msg-id 2044f630-7deb-16b8-423f-cbc8ec37ab60@pgmasters.net
Whole thread Raw
In response to Re: [HACKERS] increasing the default WAL segment size  (Beena Emerson <memissemerson@gmail.com>)
Responses Re: [HACKERS] increasing the default WAL segment size  (Robert Haas <robertmhaas@gmail.com>)
List pgsql-hackers
Hi Beena,

On 3/20/17 2:07 PM, Beena Emerson wrote:
> Added check for the version, the SHOW command will be run only in v10
> and above. Previous versions do not need this.

I've just had the chance to have a look at this patch.  This is not a 
complete review, just a test of something I've been curious about.

With 16MB WAL segments the filename neatly aligns with the LSN.  For 
example:

WAL FILE 0000000100000001000000FE = LSN 1/FE000000

This no longer holds true with this patch.  I created a cluster with 1GB 
segments and the sequence looked like:

000000010000000000000001
000000010000000000000002
000000010000000000000003
000000010000000100000000

Whereas I had expected something like:

000000010000000000000040
000000010000000000000080
0000000100000000000000CO
000000010000000100000000

I scanned the thread but couldn't find any mention of this so I'm 
curious to know if it was considered? Was the prior correspondence 
merely serendipitous?

I'm honestly not sure which way I think is better, but I know either way 
it represents a pretty big behavioral change for any tools looking at 
pg_wal or using the various helper functions.

It's a probably a good thing to do at the same time as the rename, just 
want to make sure we are all aware of the changes.

-- 
-David
david@pgmasters.net



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