These measurements tell you the amount of user data stored in the memtables, not the amount of heap used to store it, so the same applies.
On 4 June 2014 11:04, Idrén, Johan <johan.id...@dice.se> wrote: > I'm not measuring memtable size by looking at the sstables on disk, no. > I'm looking through the JMX data. So I would believe (or hope) that I'm > getting relevant data. > > > If I have a heap of 10GB and set the memtable usage to 20GB, I would > expect to hit other problems, but I'm not seeing memory usage over 10GB for > the heap, and the machine (which has ~30gb of memory) is showing ~10GB > free, with ~12GB used by cassandra, the rest in caches. > > > Reading 8k rows/s, writing 2k rows/s on a 3 node cluster. So it's not > idling. > > > BR > > Johan > > > ------------------------------ > *From:* Benedict Elliott Smith <belliottsm...@datastax.com> > *Sent:* Wednesday, June 4, 2014 11:56 AM > *To:* user@cassandra.apache.org > *Subject:* Re: memtable mem usage off by 10? > > If you are storing small values in your columns, the object overhead is > very substantial. So what is 400Mb on disk may well be 4Gb in memtables, so > if you are measuring the memtable size by the resulting sstable size, you > are not getting an accurate picture. This overhead has been reduced by > about 90% in the upcoming 2.1 release, through tickets 6271 > <https://issues.apache.org/jira/browse/CASSANDRA-6271>, 6689 > <https://issues.apache.org/jira/browse/CASSANDRA-6689> and 6694 > <https://issues.apache.org/jira/browse/CASSANDRA-6694>. > > > On 4 June 2014 10:49, Idrén, Johan <johan.id...@dice.se> wrote: > >> Hi, >> >> >> I'm seeing some strange behavior of the memtables, both in 1.2.13 and >> 2.0.7, basically it looks like it's using 10x less memory than it should >> based on the documentation and options. >> >> >> 10GB heap for both clusters. >> >> 1.2.x should use 1/3 of the heap for memtables, but it uses max ~300mb >> before flushing >> >> >> 2.0.7, same but 1/4 and ~250mb >> >> >> In the 2.0.7 cluster I set the memtable_total_space_in_mb to 4096, >> which then allowed cassandra to use up to ~400mb for memtables... >> >> >> I'm now running with 20480 for memtable_total_space_in_mb and cassandra >> is using ~2GB for memtables. >> >> >> Soo, off by 10 somewhere? Has anyone else seen this? Can't find a JIRA >> for any bug connected to this. >> >> java 1.7.0_55, JNA 4.1.0 (for the 2.0 cluster) >> >> >> BR >> >> Johan >> > >
