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The "FAQ" page has been changed by Alan Malloy. The comment on this change is: Describe how to create a TimeUUID from a java.util.Date. http://wiki.apache.org/cassandra/FAQ?action=diff&rev1=99&rev2=100 -------------------------------------------------- return buffer; } }}} + Further, it is often useful to create a TimeUUID object from some time other than the present: for example, to use as the lower bound in a SlicePredicate to retrieve all columns whose TimeUUID comes after time ''X''. Most libraries don't provide this functionality, probably because this breaks the "Universal" part of UUID: '''this should give you pause'''! Never assume such a UUID is unique: use it only as a marker for a specific time. + + With those disclaimers out of the way, if you feel a need to create a TimeUUID based on a specific date, here is some code that will work: + + {{{ + public static java.util.UUID uuidForDate(Date d) + { + /* + Magic number obtained from #cassandra's thobbs, who + claims to have stolen it from a Python library. + */ + final long NUM_100NS_INTERVALS_SINCE_UUID_EPOCH = 0x01b21dd213814000L; + + long origTime = d.getTime(); + long time = origTime * 10000 + NUM_100NS_INTERVALS_SINCE_UUID_EPOCH; + long timeLow = time & 0xffffffffL; + long timeMid = time & 0xffff00000000L; + long timeHi = time & 0xfff000000000000L; + long upperLong = (timeLow << 32) | (timeMid >> 16) | (1 << 12) | (timeHi >> 48) ; + return new java.util.UUID(upperLong, 0xC000000000000000L); + } + }}} <<Anchor(i_deleted_what_gives)>> == I delete data from Cassandra, but disk usage stays the same. What gives? == @@ -266, +288 @@ == Is there a GUI admin tool for Cassandra? == The closest is [[http://github.com/driftx/chiton|chiton]], a GTK data browser. - Another java UI [[http://code.google.com/p/cassandra-gui]], a Swing data browser. + Another java UI http://code.google.com/p/cassandra-gui, a Swing data browser. <<Anchor(a_long_is_exactly_8_bytes)>> @@ -327, +349 @@ <<Anchor(logging_using_cassandra)>> == Are there ways to do logging directly to Cassandra? == - For information on logging directly to Cassandra, see LoggingToCassandra. <<Anchor(rhel_selinux)>> == On RHEL nodes are unable to join the ring == - Check if selinux is on, if it is turn it OFF <<Anchor(auth)>> == Is there an authentication/authorization mechanism for Cassandra? == - Yes. For details, see ExtensibleAuth. <<Anchor(bulkloading)>> == How do I bulk load data into Cassandra? == - See BulkLoading <<Anchor(unsubscribe)>> == How do I unsubscribe from the email list? == - Send an email to [email protected]
