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= HBase Versions =

There are currently two active branches of HBase:
 * '''0.20''' - the current stable release series, being maintained with 
patches for bug fixes only. This release series does '''not''' support HDFS 
durability - edits may be lost in the case of node failure.
 * '''0.89''' - a development release series with active feature and stability 
development, not currently recommended for production use. This release 
'''does''' support HDFS durability - cases in which edits are lost are 
considered serious bugs.

== 0.20 Series ==

The 0.20 series was first released in fall of 2009. It is in use in production 
in a number of deployments. Development of new features and improvements is 
largely halted on this release series, though it will continue to have bug 
fixes applied, so long as the bug fixes do not have high risk of regressions.

== 0.89 "Development" Series ==

The 0.89 series is a departure from the previous sequential (0.18, 0.19, 0.20) 
versioning. Here is a short FAQ describing the version numbering and purpose of 
this series:

=== Why skip from 0.20 to 0.89? ===

The last few releases of HBase have been in lockstep with Hadoop releases (eg 
hbase 0.X.* would work with Hadoop 0.X.*). However, Hadoop's release process 
has slowed down, and we have the desire to release HBase on a different 
timeline from Hadoop, with each HBase release potentially being compatible with 
multiple versions of Hadoop. To signify this departure from lockstep releases, 
and since we intend for the next release of HBase to continue to support Hadoop 
0.20, we don't want to call the next release 0.21.

There's also a general sentiment that, feature-wise, HBase is nearing a 1.0 
level. The project has implemented the majority of the features described in 
the Bigtable paper plus many more. It's also starting to take a more central 
role in the production infrastructures of many companies. So, we'd really like 
to do a 1.0 release some time in the coming year (no dates, but maybe early 
2011?) However, we're not at 1.0 yet. There are still stability bugs to iron 
out, and some features in progress that we'd like to have done for 1.0.

So, given that, the next stable release will be called HBase 0.90. This 
indicates (a) a big step up from 0.20, (b) we are nearing 1.0, and (c) we are 
not tied to Hadoop version numbering.

We're not ready to release 0.90 yet - there are a lot of blockers still open 
affecting reliability and stability, and we haven't done extensive testing of 
trunk under production workloads. But, the development community feels there's 
a lot of stuff in trunk that's worth showing to the user community. To that 
end, we are releasing a series of development builds cut from trunk leading up 
to the 0.90 release. This release series is going to be called 0.89.

Users familiar with Linux kernel development from several years back will 
recall that Linux 2.3.* was a development series leading up to Linux 2.4, and 
Linux 2.5 led up to Linux 2.6. We have not decided to go with a strict odd/even 
for HBase for all future releases, but this particular release is similar to 
that process.

=== What will version numbers look like in the 0.89 series? ===

This development series will have version numbers 0.89.YYYYMMDD, the last 
segment of the version number indicating the date on which the release was 
branched from trunk. These releases won't have followup patch releases, and 
will only go through basic cluster testing, but provide usable snapshots of 
trunk development so that the community can begin to work with the new code and 
provide early feedback based on their use cases and testing. We're confident 
this will help make 0.90 the most stable release yet.

If there is a bug found in a release 0.89.YYYYMMDD, we will '''not''' release 
0.89.YYYYMMDD.1. All releases in this series will be new branches from trunk. 
This is to ensure that we are making forward progress towards our larger goals 
for 0.90, and to reduce maintenance burden on the development team.

=== What releases have been made on the 0.89 series? ===

The first release in the 0.89 series will be 0.89.20100621, due to be released 
the week of 6/21/2010.

=== Are the 0.89 releases official releases? ===

Yes, these releases have been voted on by the HBase development team, and 
considered official releases with regard to license policies, etc. The two main 
differences between this release series and a stable series are (a) no followup 
bugfix releases to any individual release, and (b) a lower bar for spit and 
polish, testing, etc.

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