On 3/21/17 9:04 AM, Stephen Frost wrote:
Robert,
* Robert Haas (robertmh...@gmail.com) wrote:
On Mon, Mar 20, 2017 at 7:23 PM, David Steele <da...@pgmasters.net> wrote:
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.
It is already possible to change the WAL segment size using the
configure option --with-wal-segsize, and I think the patch should be
consistent with whatever that existing option does.
Considering how little usage that option has likely seen (I can't say
I've ever run into usage of it so far...), I'm not really sure that it
makes sense to treat it as final when we're talking about changing the
default here.
+1. A seldom-used compile-time option does not necessarily provide a
good model for a user-facing feature.
In short, I'm also concerned about this change to make WAL file names no
longer match up with LSNs and also about the odd stepping that you get
as a result of this change when it comes to WAL file names.
I can't decide which way I like best. I like the filenames
corresponding to LSNs as they do now, but it seems like a straight
sequence might be easier to understand. Either way you need to know
that different segment sizes mean different numbers of segments per
lsn.xlogid.
Even now the correspondence is a bit tenuous. I've always thought:
00000001000000010000000F
Should be:
00000001000000010F000000
I'm really excited to (hopefully) have this feature in v10. I just want
to be sure we discuss this as it will be a big change for tool authors
and just about anybody who looks at WAL.
Thanks,
--
-David
da...@pgmasters.net
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