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From Anishek Agarwal <anis...@gmail.com>
Subject Heap memory usage while writing
Date Thu, 09 Apr 2015 06:30:58 GMT
Hello,

We have only on CF as

CREATE TABLE t1(id bigint, ts timestamp, definition text, primary key (id,
ts))
with clustering order by (ts desc) and gc_grace_seconds=0
and compaction = {'class': 'DateTieredCompactionStrategy',
'timestamp_resolution':'SECONDS', 'base_time_seconds':'20',
'max_sstable_age_days':'30'}
and compression={'sstable_compression' : ''};

on a single Node using the following in

cassandra.yaml:::::
memtable_total_space_in_mb: 2048
commitlog_total_space_in_mb: 4096
memtable_flush_writers: 2
memtable_flush_queue_size: 1

cassandra-env.sh ::::
MAX_HEAP_SIZE="8G"
HEAP_NEWSIZE="5120M"
JVM_OPTS="$JVM_OPTS -XX:+UseParNewGC"
JVM_OPTS="$JVM_OPTS -XX:+UseConcMarkSweepGC"
JVM_OPTS="$JVM_OPTS -XX:+CMSParallelRemarkEnabled"
JVM_OPTS="$JVM_OPTS -XX:SurvivorRatio=6"
JVM_OPTS="$JVM_OPTS -XX:MaxTenuringThreshold=1"
JVM_OPTS="$JVM_OPTS -XX:CMSInitiatingOccupancyFraction=70"
JVM_OPTS="$JVM_OPTS -XX:+UseCMSInitiatingOccupancyOnly"
JVM_OPTS="$JVM_OPTS -XX:+UseTLAB"
JVM_OPTS="$JVM_OPTS -XX:MaxPermSize=256m"
JVM_OPTS="$JVM_OPTS -XX:+AggressiveOpts"
JVM_OPTS="$JVM_OPTS -XX:+UseCompressedOops"
JVM_OPTS="$JVM_OPTS -XX:+CMSIncrementalMode"
JVM_OPTS="$JVM_OPTS -XX:+CMSIncrementalPacing"
JVM_OPTS="$JVM_OPTS -XX:+PrintGCDetails"
JVM_OPTS="$JVM_OPTS -XX:+PrintGCTimeStamps -verbose:gc"
JVM_OPTS="$JVM_OPTS
-Xloggc:/home/anishek/apache-cassandra-2.0.13/logs/gc.log"
JVM_OPTS="$JVM_OPTS -XX:+PrintHeapAtGC"
JVM_OPTS="$JVM_OPTS -XX:+PrintTenuringDistribution"


I am writing via 20 threads continuously to this table above.
I see that some data keeps moving from the young generation to the older
generation continuously.

I am wondering why this is happening. Given i am writing constantly and my
young generation is more than twice the max mem table space used i would
think only the young generation space would be used and nothing would ever
go old generation.

** System.log show no compactions happening.
** There are no read operations.
** Cassandra version 2.0.13 on centos with 16 cores and 16 GB Ram

Thanks
Anishek

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