Jul 29, 2011

Do not use Java 7 yet

The 7th release of Java today seems that introduced some nasty bugs caused by hotspot compiler optimizations miscompiling some loops. Code containing loops will propably be affected by this bug.


If you use Java 7 use this switch when starting the JVM:
-XX:-UseLoopPredicate

Uwe Schindler an Apache Lucene PMC Member tweeted a warning earlier today as the bug affected Apache Lucene and Solr project causing wrong compilation of some loops.

The warning mail and the full story from LucidImagination:

From: Uwe Schindler
Date: Thu, 28 Jul 2011 23:13:36 +0200
Subject: [WARNING] Index corruption and crashes in Apache Lucene Core / Apache Solr with Java 7

Hello Apache Lucene & Apache Solr users,
Hello users of other Java-based Apache projects,

Oracle released Java 7 today. Unfortunately it contains hotspot compiler
optimizations, which miscompile some loops. This can affect code of several
Apache projects. Sometimes JVMs only crash, but in several cases, results
calculated can be incorrect, leading to bugs in applications (see Hotspot
bugs 7070134 [1], 7044738 [2], 7068051 [3]).

Apache Lucene Core and Apache Solr are two Apache projects, which are
affected by these bugs, namely all versions released until today. Solr users
with the default configuration will have Java crashing with SIGSEGV as soon
as they start to index documents, as one affected part is the well-known
Porter stemmer (see LUCENE-3335 [4]). Other loops in Lucene may be
miscompiled, too, leading to index corruption (especially on Lucene trunk
with pulsing codec; other loops may be affected, too - LUCENE-3346 [5]).

These problems were detected only 5 days before the official Java 7 release,
so Oracle had no time to fix those bugs, affecting also many more
applications. In response to our questions, they proposed to include the
fixes into service release u2 (eventually into service release u1, see [6]).
This means you cannot use Apache Lucene/Solr with Java 7 releases before
Update 2! If you do, please don't open bug reports, it is not the
committers' fault! At least disable loop optimizations using the
-XX:-UseLoopPredicate JVM option to not risk index corruptions.

Please note: Also Java 6 users are affected, if they use one of those JVM
options, which are not enabled by default: -XX:+OptimizeStringConcat or
-XX:+AggressiveOpts

It is strongly recommended not to use any hotspot optimization switches in
any Java version without extensive testing!

In case you upgrade to Java 7, remember that you may have to reindex, as the
unicode version shipped with Java 7 changed and tokenization behaves
differently (e.g. lowercasing). For more information, read
JRE_VERSION_MIGRATION.txt in your distribution package!

On behalf of the Lucene project,
Uwe

[1] http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7070134
[2] http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7044738
[3] http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7068051
[4] https://issues.apache.org/jira/browse/LUCENE-3335
[5] https://issues.apache.org/jira/browse/LUCENE-3346
[6] http://s.apache.org/StQ

Better play safe and expect an update form Oracle i guess...
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