http://www.datastax.com/support-forums/topic/cassandra-caching-questions Software, Support, and Training for Apache Cassandra en-US Mon, 20 May 2013 05:33:59 +0000 http://bbpress.org/?v=1.0.3 q http://www.datastax.com/support-forums/search.php http://www.datastax.com/support-forums/topic/cassandra-caching-questions#post-1694 Wed, 18 Apr 2012 19:04:19 +0000 joaquin 1694@http://www.datastax.com/support-forums/ <p>To answer your other questions:<br /> 3. These settings are cluster level and not node level, right?</p> <p>Correct, almost all settings that can be changed via CQL and the cassandra-cli are cluster level.<br /> The cassandra.yaml and cassandra-env.sh file are, for the most part, node level. If set incorrectly according to cluster settings, you will error out and not be able to join the cluster as a safety measure.</p> <p>4. When inserting into the Cassandra cluster, before the MemTable is flushed to the SSTable, if we make a query to data that is currently in the MemTable, will it fetch it directly from memory (MemTable) then? Will the MemTable memory (for inserts) share the same configuration (row/key cache size) and space as the cache memory for reads?</p> <p>Yes, queries will check the MemTables first, then cache, then disk. </p> <p>No, these are two different spaces. Memtables can be configured in the cassandra.yaml, but the default of 1/3 of your total heap space is typically a great setting.</p> <p>Thanks,<br /> Joaquin </p> http://www.datastax.com/support-forums/topic/cassandra-caching-questions#post-1627 Sun, 15 Apr 2012 20:18:04 +0000 khahn 1627@http://www.datastax.com/support-forums/ <p>Another correction: The row_cache_save_period_in_seconds and key_cache_save_period_in_seconds are obsolete. They no longer do anything. Sorry for the confusion. </p> http://www.datastax.com/support-forums/topic/cassandra-caching-questions#post-1624 Sat, 14 Apr 2012 23:24:57 +0000 khahn 1624@http://www.datastax.com/support-forums/ <p>Regarding your question 5, please see <a href="http://www.datastax.com/docs/1.0/operations/tuning" rel="nofollow">http://www.datastax.com/docs/1.0/operations/tuning</a>. </p> http://www.datastax.com/support-forums/topic/cassandra-caching-questions#post-1623 Sat, 14 Apr 2012 22:06:46 +0000 khahn 1623@http://www.datastax.com/support-forums/ <p>Correction: Use CLI. For example, <a href="http://comments.gmane.org/gmane.comp.db.cassandra.user/21967" rel="nofollow">http://comments.gmane.org/gmane.comp.db.cassandra.user/21967</a> </p> http://www.datastax.com/support-forums/topic/cassandra-caching-questions#post-1622 Sat, 14 Apr 2012 19:15:45 +0000 khahn 1622@http://www.datastax.com/support-forums/ <p>To answer your first question, you can use CQLsh 2.0 to set these column family attributes. For example, ALTER TABLE addamsFamily WITH comment = 'A most excellent and useful column family' AND row_cache_save_period_in_seconds = 1;</p> <p>Here is more information from our docs: </p> <p>key_cache_save_period_in_seconds<br /> Sets number of seconds between saving key caches: the key caches can be saved<br /> periodically, and if one exists on startup it will be loaded. This property is called <code></code>key_cache_save_period<code></code> in the <code></code>cassandra-cli<code></code> client.</p> <p>row_cache_save_period_in_seconds<br /> Sets the number of seconds between saving row caches: the row caches can be saved periodically, and if one exists on startup it will be loaded.</p> <p>Sorry, I can only provide a partial response. Hope it helps. </p> http://www.datastax.com/support-forums/topic/cassandra-caching-questions#post-1597 Thu, 12 Apr 2012 01:28:16 +0000 Anonymous 1597@http://www.datastax.com/support-forums/ <p>Hi friends,</p> <p>I am currently doing read performance tuning and had a few questions on Cassandra caching:</p> <p>From describe keyspace, I see these two settings under the ColumnFamily section:<br /> Row cache size / save period in seconds / keys to save : 0.0/0/all<br /> Key cache size / save period in seconds: 200000.0/14400</p> <p>1. I understand the row/key cache sizes can be set, how is the save period in seconds set?<br /> 2. If there is x rows in cache, will these rows get flushed regardless after however many seconds set above in the save period (even if the cache doesn’t fill up)?<br /> 3. These settings are cluster level and not node level, right?<br /> 4. When inserting into the Cassandra cluster, before the MemTable is flushed to the SSTable, if we make a query to data that is currently in the MemTable, will it fetch it directly from memory (MemTable) then? Will the MemTable memory (for inserts) share the same configuration (row/key cache size) and space as the cache memory for reads?<br /> 5. How does the caching mechanism work? Least recently read, first to leave the cache?</p> <p>I know this is quite a few questions, partial responses would be awesome too. Thanks so much in advance!</p> <p>Regards,<br /> Alvin </p>