That does not sound right. 

If you have the time can you create a jira ticket describing the problem, please include:

* the GC logs gathered by enabling them here https://github.com/apache/cassandra/blob/trunk/conf/cassandra-env.sh#L165 (It would be good to see the node get into trouble if possible).
* OS, JVM and cassandra versions
* information on the schema and workload
* anything else you think is important. 


Aaron Morton
Freelance Developer

On 6/06/2012, at 7:24 AM, Mina Naguib wrote:

Hi Wade

I don't know if your scenario matches mine, but I've been struggling with memory pressure in 1.x as well.  I made the jump from 0.7.9 to 1.1.0, along with enabling compression and levelled compactions, so I don't know which specifically is the main culprit.

Specifically, all my nodes seem to "lose" heap memory.  As parnew and CMS do their job, over any reasonable period of time, the "floor" of memory after a GC keeps rising.  This is quite visible if you leave jconsole connected for a day or so, and manifests itself as a funny-looking cone like so: http://mina.naguib.ca/images/cassandra_jconsole.png

Once memory pressure reaches a point where the heap can't be maintained reliably below 75%, cassandra goes into survival mode - via a bunch of tunables in cassandra.conf it'll do things like flush memtables, drop caches, etc - all of which, in my experience, especially with the recent off-heap data structures, exasperate the problem.

I've been meaning, of course, to collect enough technical data to file a bug report, but haven't had the time.  I have not yet tested 1.1.1 to see if it improves the situation.

What I have found however, is a band-aid which you see at the rightmost section of the graph in the screenshot I posted.  That is simply to hit "Perform GC" button in jconsole.  It seems that a full System.gc() *DOES* reclaim heap memory that parnew and CMS fail to reclaim.

On my production cluster I have a full-GC via JMX scheduled in a rolling fashion every 4 hours.  It's extremely expensive (20-40 seconds of unresponsiveness) but is a necessary evil in my situation.  Without it, my nodes enter a nasty spiral of constant flushing, constant compactions, high heap usage, instability and high latency.

On 2012-06-05, at 2:56 PM, Poziombka, Wade L wrote:

Alas, upgrading to 1.1.1 did not solve my issue.

-----Original Message-----
From: Brandon Williams [mailto:driftx@gmail.com]
Sent: Monday, June 04, 2012 11:24 PM
To: user@cassandra.apache.org
Subject: Re: memory issue on 1.1.0

Perhaps the deletes: https://issues.apache.org/jira/browse/CASSANDRA-3741


On Sun, Jun 3, 2012 at 6:12 PM, Poziombka, Wade L <wade.l.poziombka@intel.com> wrote:
Running a very write intensive (new column, delete old column etc.) process and failing on memory.  Log file attached.

Curiously when I add new data I have never seen this have in past sent
hundreds of millions "new" transactions.  It seems to be when I
modify.  my process is as follows

key slice to get columns to modify in batches of 100, in separate threads modify those columns.  I advance the slice with the start key each with last key in previous batch.  Mutations done are update a column value in one column family(token), delete column and add new column in another (pan).

Runs well until after about 5 million rows then it seems to run out of memory.  Note that these column families are quite small.

WARN [ScheduledTasks:1] 2012-06-03 17:49:01,558 GCInspector.java (line
145) Heap is 0.7967470834946492 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
INFO [ScheduledTasks:1] 2012-06-03 17:49:01,559 StorageService.java
(line 2772) Unable to reduce heap usage since there are no dirty
column families
INFO [GossipStage:1] 2012-06-03 17:49:01,999 Gossiper.java (line 797)
InetAddress / is now UP
INFO [ScheduledTasks:1] 2012-06-03 17:49:10,048 GCInspector.java
(line 122) GC for ParNew: 206 ms for 1 collections, 7345969520 used;
max is 8506048512
INFO [ScheduledTasks:1] 2012-06-03 17:49:53,187 GCInspector.java
(line 122) GC for ConcurrentMarkSweep: 12770 ms for 1 collections,
5714800208 used; max is 8506048512

Keyspace: keyspace
      Read Count: 50042632
      Read Latency: 0.23157864418482224 ms.
      Write Count: 44948323
      Write Latency: 0.019460829472992797 ms.
      Pending Tasks: 0
              Column Family: pan
              SSTable count: 5
              Space used (live): 1977467326
              Space used (total): 1977467326
              Number of Keys (estimate): 16334848
              Memtable Columns Count: 0
              Memtable Data Size: 0
              Memtable Switch Count: 74
              Read Count: 14985122
              Read Latency: 0.408 ms.
              Write Count: 19972441
              Write Latency: 0.022 ms.
              Pending Tasks: 0
              Bloom Filter False Postives: 829
              Bloom Filter False Ratio: 0.00073
              Bloom Filter Space Used: 37048400
              Compacted row minimum size: 125
              Compacted row maximum size: 149
              Compacted row mean size: 149

              Column Family: token
              SSTable count: 4
              Space used (live): 1250973873
              Space used (total): 1250973873
              Number of Keys (estimate): 14217216
              Memtable Columns Count: 0
              Memtable Data Size: 0
              Memtable Switch Count: 49
              Read Count: 30059563
              Read Latency: 0.167 ms.
              Write Count: 14985488
              Write Latency: 0.014 ms.
              Pending Tasks: 0
              Bloom Filter False Postives: 13642
              Bloom Filter False Ratio: 0.00322
              Bloom Filter Space Used: 28002984
              Compacted row minimum size: 150
              Compacted row maximum size: 258
              Compacted row mean size: 224

              Column Family: counters
              SSTable count: 2
              Space used (live): 561549994
              Space used (total): 561549994
              Number of Keys (estimate): 9985024
              Memtable Columns Count: 0
              Memtable Data Size: 0
              Memtable Switch Count: 38
              Read Count: 4997947
              Read Latency: 0.092 ms.
              Write Count: 9990394
              Write Latency: 0.023 ms.
              Pending Tasks: 0
              Bloom Filter False Postives: 191
              Bloom Filter False Ratio: 0.37525
              Bloom Filter Space Used: 18741152
              Compacted row minimum size: 125
              Compacted row maximum size: 179
              Compacted row mean size: 150