[tz] [PATCH 2/3] Replace some zones with links when that doesn't lose non-LMT info.

Paul Eggert eggert at cs.ucla.edu
Wed Sep 4 14:32:56 UTC 2013

Stephen Colebourne wrote:

> ubiquity is a key value of the data. The same data is used
> everywhere from Unix to Java to mobile phones.

No, it's pretty routinely filtered before it hits many
platforms.  One example: QNX has unsigned time_t, which by
design filters out all data before 1970.

Furthermore, there is an inevitable delay in propagating
changes to the field.  Even if we're talking a single host
with 64-bit signed time_t (so that it matches Java's
'long'), I've seen situations where Java's copy of the data
disagree with the POSIX copy.  And certainly a distributed
application cannot assume ubiquity, as the client and server
may be updated at different times.  So, for various reasons
unrelated to the proposed changes, it's already the case
that applications cannot assume that the data are ubiquitous
and that the same data are used everywhere.

That's not to say that we should introduce changes merely
for the sake of changes; far from it.  I agree with you that
stability is a good property.  But we shouldn't be inhibited
from change because of the goal of having the data be the
same everywhere.  That goal is unattainable, and always has

> I'm not speaking on behalf of myself, but on behalf of Java
> development generally.

These comments would have more weight if they pointed to
user problems that occurred when we made similar changes in
the past.  Based on my experience I'm skeptical that there
were significant user problems.  I've asked the list for
reports of problems but nobody else has reported problems
either.  This suggests that the concerns are misplaced.

On this list I have also noted that the changes promise to
make life easier for users in some cases, by omitting
irrelevant choices.  This is a real advantage that should
trump stability concerns.

> the leading supporters of Paul's approach are
> from an academic background (Paul, Guy, yourself)

This appears to be based on a misconception.  I won't speak
for Guy and Russ, but my career has been spent more in
industry than in academia.  I developed most of the tz
database while in industry: I worked on enterprise software,
and built several distributed applications involving many
clients and using the tz database.  I am attempting to use
the tz maintenance practices that I used while in industry.

> the recent batch of changes are far in
> excess of what has happened over previous years.

Sometimes I get up the energy to fix things.  Often I don't.
(Let's not be looking at gift horses in the mouth. :-)

> zone ID merging that loses the start date of offsets or abbreviations,
> even if those are guesswork/invented (because the replacement is not
> an enhancement, its worse).

I've had quite a bit of experience in dealing with the
Shanks data.  From my experience the proposed change is a
fairer representation of what we know than the previous
version was.  You're right that we don't know that the new
version is correct and the old is wrong (both are guesses),
but it's not right to say that the new version is worse.

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