Hstore is a part of PostgreSQL distribution since 8.2 version !
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Changes: functions ''isexists'' and ''isdefined'' were renamed to 
''exist'' and ''defined''. 
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Users of old versions encouraged to upgrade.
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<a href="http://www.sai.msu.su/~megera/wiki/Hstore">Online documentation</a>
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Old (unsupported) version: <a href="hstore.tar.gz">hstore.tar.gz</a>