Re: increasing the default WAL segment size

* Peter Eisentraut (peter(dot)eisentraut(at)2ndquadrant(dot)com) wrote:
> The question is, which property is more useful to preserve: matching
> LSN, or having a mostly consecutive numbering.
>
> Actually, I would really really like to have both, but if I had to pick
> one, I'd lean 55% toward consecutive numbering.

> For the issue at hand, I think it's fine to proceed with the naming
> schema that the existing compile-time option gives you.

What I don't particularly like about that is that it's *not* actually
consecutive, you end up with this:

000000010000000000000001
000000010000000000000002
000000010000000000000003
000000010000000100000000

Which is part of what I don't particularly like about this approach.

> In fact, that would flush out some of the tools that look directly at
> the file names and interpret them, thus preserving the option to move to
> a more radically different format.

This doesn't make a lot of sense to me. If we get people to change to
using larger WAL segments and the tools are modified to understand the
pseudo-consecutive format, and then you want to change it on them again
in another release or two? I'm generally a fan of not feeling too bad
breaking backwards compatibility, but it seems pretty rough even to me
to do so immediately.

This is exactly why I think it'd be better to work out a good naming
scheme now that actually makes sense and that we'll be able to stick
with for a while instead of rushing to get this ability in now, when
we'll have people actually starting to use it and then try to change it.

> If changing WAL sizes catches on, I do think we should keep thinking
> about a new format for a future release, because debugging will
> otherwise become a bit wild. I'm thinking something like
>
> {integer timeline}_{integer seq number}_{hex lsn}
>
> might address various interests.

Right, I'd rather not have debugging WAL files become a bit wild.

If we can't work out a sensible approach to naming that we expect to
last us for at least a couple of releases for different sizes of WAL
files, then I don't think we should rush to encourage users to use
different sizes of WAL files.

Thanks!

Stephen