Re: wal_sync_method as enum

Attached patch implements wal_sync_method as an enum. I'd like someone
to look it over before I apply it - I don't have the machines to test
all codepaths (and some of it is hard to test - better to read it and
make sure it's right).

In order to implement the enum guc, I had to break out a new
SYNC_METHOD_OPEN_DSYNC out of SYNC_METHOD_OPEN where it was previously
overloaded. This is one of the parts where I'm slightly worried I have
made a mistake.

//Magnus

Magnus Hagander wrote:
> Attached patch implements wal_sync_method as an enum. I'd like someone
> to look it over before I apply it - I don't have the machines to test
> all codepaths (and some of it is hard to test - better to read it and
> make sure it's right).
>
> In order to implement the enum guc, I had to break out a new
> SYNC_METHOD_OPEN_DSYNC out of SYNC_METHOD_OPEN where it was previously
> overloaded. This is one of the parts where I'm slightly worried I have
> made a mistake.

I took a look at this and I like it -- it seems correct as far as I can
tell, and it has the nice property that we can display the list of
values that the current platform actually support.

This thing looked a bit dubious to me at first:

> ! switch (new_sync_method)
> {
> ! case SYNC_METHOD_FSYNC:
> ! case SYNC_METHOD_FSYNC_WRITETHROUGH:
> ! case SYNC_METHOD_FDATASYNC:

because at least some of the values are only present on some platforms.
However, I think realized that the actual values are present on all
platforms, independent of whether they represent a supported fsync
method, so this is OK. Perhaps it would be good to add a comment on top
of the switch statement explaining this. Otherwise looks fine.

Well, and the ereport("FIXME") needs to be improved :-)

--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

Alvaro Herrera wrote:
> Magnus Hagander wrote:
> > Attached patch implements wal_sync_method as an enum. I'd like
> > someone to look it over before I apply it - I don't have the
> > machines to test all codepaths (and some of it is hard to test -
> > better to read it and make sure it's right).
> >
> > In order to implement the enum guc, I had to break out a new
> > SYNC_METHOD_OPEN_DSYNC out of SYNC_METHOD_OPEN where it was
> > previously overloaded. This is one of the parts where I'm slightly
> > worried I have made a mistake.
>
> I took a look at this and I like it -- it seems correct as far as I
> can tell, and it has the nice property that we can display the list of
> values that the current platform actually support.

Yeah, this was one of the "most helpful ones" I thought of when I
started working on the enum stuff. It just also happened to be the one
that required the most changes :-S It'll be very good for tools like
[php]pgadmin to be able to show which values are actually supported.

> This thing looked a bit dubious to me at first:
>
> > ! switch (new_sync_method)
> > {
> > ! case SYNC_METHOD_FSYNC:
> > ! case SYNC_METHOD_FSYNC_WRITETHROUGH:
> > ! case SYNC_METHOD_FDATASYNC:
>
> because at least some of the values are only present on some
> platforms. However, I think realized that the actual values are
> present on all platforms, independent of whether they represent a
> supported fsync method, so this is OK. Perhaps it would be good to
> add a comment on top of the switch statement explaining this.
> Otherwise looks fine.

Will add comment. I used to have #ifdefs there from the old code, but
it's a lot more readable this way... Even more readable with the
comment, of course.

> Well, and the ereport("FIXME") needs to be improved :-)

Pah, details, details :-) It was just a copy/paste after all...

//Magnus