http://www.datastax.com/support-forums/topic/ttl-usage Software, Support, and Training for Apache Cassandra en-US Wed, 22 May 2013 22:13:02 +0000 http://bbpress.org/?v=1.0.3 q http://www.datastax.com/support-forums/search.php http://www.datastax.com/support-forums/topic/ttl-usage#post-1193 Tue, 21 Feb 2012 19:13:04 +0000 nickmbailey 1193@http://www.datastax.com/support-forums/ <p>Timezones should not matter to cassandra, provided you have them configured correctly. What is important is that the system clocks on the nodes are synchronized using NTP.</p> <p>Cassandra will use unix timestamps (<a href="http://en.wikipedia.org/wiki/Unix_time" rel="nofollow">http://en.wikipedia.org/wiki/Unix_time</a>) for calculating the ttl expiration. Unix timestamps are timezone agnostic. You can see what I mean pretty easily using the date command in a unix environment:</p> <p>$ date<br /> Tue Feb 21 13:11:31 CST 2012<br /> $ TZ=America/Los_Angeles date<br /> Tue Feb 21 11:11:36 PST 2012<br /> $ date +%s<br /> 1329851504<br /> $ TZ=America/Los_Angeles date +%s<br /> 1329851508 </p> http://www.datastax.com/support-forums/topic/ttl-usage#post-1187 Tue, 21 Feb 2012 08:22:12 +0000 Anonymous 1187@http://www.datastax.com/support-forums/ <p>Aside from the system clocks requirement (which kinda make the problem go away), the answer is not definitive to me; the calculated expire time, does it contain a timezone? </p> <p>So in my example, given that I insert a column on 2012-02-21T00:00:00+00:00 with a TTL of 25 hours, the expire time becomes 2012-02-22T01:00:00+00:00, or 2012-02-22 01:00 zulu. </p> <p>When synced with a node in GMT+1, where we will assume that the system clock also is on GTM+1, if the expire time holds the timezone, it can easily be converted to the system clock, so on this server the expire time is 2012-02-22 02:00 zulu. Does Cassandra work like this? Or is having the system clock of all nodes at GMT a must? </p> http://www.datastax.com/support-forums/topic/ttl-usage#post-1176 Sat, 18 Feb 2012 00:59:35 +0000 rbranson 1176@http://www.datastax.com/support-forums/ <p>When an expiring column is inserted into Cassandra, the coordinator node actually transforms the TTL value provided into a timestamp based on that node's local clock (current time + TTL). The column is expired once the local clock on the queried node rolls past this expiration time.</p> <p>It's important (and a best practice) for the system clocks on all of your nodes (including the app tier) to be on UTC/GMT and regularly synchronized using NTP to avoid any issues like this.</p> <p>More information about expiring columns can be found here:</p> <p><a href="http://www.datastax.com/dev/blog/whats-new-cassandra-07-expiring-columns" rel="nofollow">http://www.datastax.com/dev/blog/whats-new-cassandra-07-expiring-columns</a> </p> http://www.datastax.com/support-forums/topic/ttl-usage#post-1170 Fri, 17 Feb 2012 08:32:59 +0000 Anonymous 1170@http://www.datastax.com/support-forums/ <p>I'm using Cassandra to store piece of information that have a natural expiration date and time. When inserting them, I calculate the TTL based on the expiration date. This should mean that when the data expires it should automatically be removed from Cassandra (given resources are available and all).</p> <p>If this column-with-TTL is sync with another Cassandra node, possibly in another timezone, will the actual time on which the TTL should delete the column change or not? </p> <p>For example, suppose I put in a column in Cassandra at 00:00 in the GMT timezone with an expire time of 25 hours. This means it will be deleted the next day at 01:00. This column is synced to a server in Germany (GMT+1). Will that copy of the column also expire at 01:00 GMT, or 02:00 local time? </p>