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From "Uwe Schindler" <>
Subject RE: Proposal about Version API "relaxation"
Date Tue, 13 Apr 2010 16:41:58 GMT
Hi Shai,


one of the problem I have is: That is a static default! We want to get rid of them (and did
it mostly, only some relicts remain), so there are no plans to reimplement such a thing again.
The badest one is BooleanQuery.maxClauseCount. The same applies to all types of sysprops.
As Lucene and solr is mostly running in servlet containers, this type of thing  makes web
applications no longer isolated. This is also a general contract for libraries: never ever
rely on sysprops or statics.





Uwe Schindler

H.-H.-Meier-Allee 63, D-28213 Bremen




From: Shai Erera [] 
Sent: Tuesday, April 13, 2010 5:27 PM
Subject: Proposal about Version API "relaxation"



I'd like to propose a relaxation on the Version API. Uwe, please read the entire email before
you reply :).

I was thinking, following a question on the user list, that the Version-based API may not
be very intuitive to users, especially those who don't care about versioning, as well as very
inconvenient. So there are two issues here:
1) How should one use Version smartly so that he keeps backwards compatibility. I think we
all know the answer, but a Wiki page with some "best practices" tips would really help users
use it.
2) How can one write sane code, which doesn't pass versions all over the place if: (1) he
doesn't care about versions, or (2) he cares, and sets the Version to the same value in his
app, in all places.

Also, I think that today we offer a flexibility to users, to set different Versions on different
objects in the life span of their application - which is a good flexibility but can also lead
people to shoot themselves in the legs if they're not careful -- e.g. upgrading Version across
their app, but failing to do so for one or two places ...

So the change I'd like to propose is to mostly alleviate (2) and better protect users - I

I was thinking that we can add on Version a DEFAULT version, which the caller can set. So
Version.setDefault and Version.getDefault will be added, as static members (more on the static-ness
of it later). We then change the API which requires Version to also expose an API which doesn't
require it, and that API will call Version.getDefault(). People can use it if they want to

Few points:
1) As a default DEFAULT Version is controversial, I don't want to propose it, even though
I think Lucene can define the DEFAULT to be the latest. Instead, I propose that Version.getDefault
throw a DefaultVersionNotSetException if it wasn't set, while an API which relies on the default
Version is called (I don't want to return null, not sure how safe it is).
2) That DEFAULT Version is static, which means it will affect all indexing code running inside
the JVM. Which is fine:
2.1) Perhaps all the indexing code should use the same Version
2.2) If you know that's not the case, then pass Version to the API which requires it - you
cannot use the 'default Version' API -- nothing changes for you.
One case is missing -- you might not know if your code is the only indexing code which runs
in the JVM ... I don't have a solution to that, but I think it'll be revealed pretty quickly,
and you can change your code then ...

So to summarize - the current Version API will remain and people can still use it. The DEFAULT
Version API is meant for convenience for those who don't want to pass Version everywhere,
for the reasons I outlined above. This will also clean our test code significantly, as the
tests will set the DEFAULT version to TEST_VERSION_CURRENT at start ...

The changes to the Version class will be very simple.

If people think that's acceptable, I can open an issue and work on it.


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