My experience (running C* 1.2.2): 1. I also observe that this occurs during compaction. 2. I have never yet seen a node recover from this state. Once it starts complaining about heap, it starts a death spiral, i.e., futile attempts to fix the situation. Eventually the node starts running GC for so long that it looks down to the other nodes. 3. Do you observe a lot of pending MemtablePostFlusher tasks in the log? I believe this is another symptom.
Like you, I would love to get advice on what causes this and how to avoid it. -----Original Message----- From: Michael Theroux [mailto:mthero...@yahoo.com] Sent: Friday, April 19, 2013 6:00 PM To: user@cassandra.apache.org Subject: Advice on memory warning Hello, We've recently upgraded from m1.large to m1.xlarge instances on AWS to handle additional load, but to also relieve memory pressure. It appears to have accomplished both, however, we are still getting a warning, 0-3 times a day, on our database nodes: WARN [ScheduledTasks:1] 2013-04-19 14:17:46,532 GCInspector.java (line 145) Heap is 0.7529240824406468 full. You may need to reduce memtable and/or cache sizes. Cassandra will now flush up to the two largest memtables to free up memory. Adjust flush_largest_memtables_at threshold in cassandra.yaml if you don't want Cassandra to do this automatically This is happening much less frequently than before the upgrade, but after essentially doubling the amount of available memory, I'm curious on what I can do to determine what is happening during this time. I am collecting all the JMX statistics. Memtable space is elevated but not extraordinarily high. No GC messages are being output to the log. These warnings do seem to be occurring doing compactions of column families using LCS with wide rows, but I'm not sure there is a direct correlation. We are running Cassandra 1.1.9, with a maximum heap of 8G. Any advice? Thanks, -Mike _______________________________________________ This message may contain information that is confidential or privileged. If you are not an intended recipient of this message, please delete it and any attachments, and notify the sender that you have received it in error. Unless specifically stated in the message or otherwise indicated, you may not duplicate, redistribute or forward this message or any portion thereof, including any attachments, by any means to any other person, including any retail investor or customer. This message is not a recommendation, advice, offer or solicitation, to buy/sell any product or service, and is not an official confirmation of any transaction. Any opinions presented are solely those of the author and do not necessarily represent those of Barclays. This message is subject to terms available at: www.barclays.com/emaildisclaimer and, if received from Barclays' Sales or Trading desk, the terms available at: www.barclays.com/salesandtradingdisclaimer/. By messaging with Barclays you consent to the foregoing. Barclays Bank PLC is a company registered in England (number 1026167) with its registered office at 1 Churchill Place, London, E14 5HP. This email may relate to or be sent from other members of the Barclays group. _______________________________________________
