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From Terje Marthinussen <tmarthinus...@gmail.com>
Subject Re: Forcing Cassandra to free up some space
Date Thu, 16 Jun 2011 02:17:11 GMT
Watching this on a node here right now and it sort of shows how bad this can
get.
This node still has 109GB free disk by the way...

INFO [CompactionExecutor:5] 2011-06-16 09:11:59,164 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:5] 2011-06-16 09:12:23,929 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:5] 2011-06-16 09:12:46,489 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:17:53,299 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:18:17,782 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:18:42,078 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:19:06,984 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:19:32,079 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:19:57,265 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:20:22,706 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:20:47,331 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:21:13,062 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:21:38,288 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:22:03,500 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:22:29,407 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:22:55,577 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:23:20,951 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:23:46,448 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:3] 2011-06-16 09:24:12,030 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [ScheduledTasks:1] 2011-06-16 09:29:29,494 GCInspector.java (line 128)
GC for ParNew: 392 ms, 398997776 reclaimed leaving 2334786808 used; max is
10844635136
 INFO [ScheduledTasks:1] 2011-06-16 09:29:32,831 GCInspector.java (line 128)
GC for ParNew: 737 ms, 332336832 reclaimed leaving 2473311448 used; max is
10844635136
 INFO [CompactionExecutor:6] 2011-06-16 09:48:00,633 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:6] 2011-06-16 09:48:26,119 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:6] 2011-06-16 09:48:49,002 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:6] 2011-06-16 10:10:20,196 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:6] 2011-06-16 10:10:45,322 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:6] 2011-06-16 10:11:07,619 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:7] 2011-06-16 11:01:45,562 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:7] 2011-06-16 11:02:10,236 StorageService.java
(line 2071) requesting GC to free disk space
 INFO [CompactionExecutor:7] 2011-06-16 11:05:31,297 StorageService.java
(line 2071) requesting GC to free disk space

If I look at the data dir, I see 46 *Compacted files which makes up an
additional 137GB of space.
The oldest of these Compacted files dates back to Jun 16th 01:26.

If these got deleted, there should actually be enough disk for the node to
run a full compaction run if needed.

Either the GC cleanup tactic is seriously flawed or  we have a potential bug
keeping references far longer than needed?

Terje



On Wed, Jun 15, 2011 at 11:50 PM, Shotaro Kamio <kamioshot@gmail.com> wrote:

> We've encountered the situation that compacted sstable files aren't
> deleted after node repair. Even when gc is triggered via jmx, it
> sometimes leaves compacted files. In a case, a lot of files are left.
> Some files stay more than 10 hours already. There is no guarantee that
> gc will cleanup all compacted sstable files.
>
> We have a great interest on the following ticket.
> https://issues.apache.org/jira/browse/CASSANDRA-2521
>
>
> Regards,
> Shotaro
>
>
> On Fri, May 27, 2011 at 11:27 AM, Jeffrey Kesselman <jeffpk@gmail.com>
> wrote:
> > Im also not sure that will guarantee all space is cleaned up.  It
> > really depends on what you are doing inside Cassandra.  If you have
> > your on garbage collect that is just in some way tied to the gc run,
> > then it will run when  it runs.
> >
> > If otoh you are associating records in your storage with specific
> > objects in memory and using one of the post-mortem hooks (finalize or
> > PhantomReference) to tell you to clean up that particular record then
> > its quite possible they wont all get cleaned up.  In general hotspot
> > does not find and clean every candidate object on every GC run.  It
> > starts with the easiest/fastest to find and then sees what more it
> > thinks it needs to do to create enough memory for anticipated near
> > future needs.
> >
> > On Thu, May 26, 2011 at 10:16 PM, Jonathan Ellis <jbellis@gmail.com>
> wrote:
> >> In summary, system.gc works fine unless you've deliberately done
> >> something like setting the -XX:-DisableExplicitGC flag.
> >>
> >> On Thu, May 26, 2011 at 5:58 PM, Konstantin  Naryshkin
> >> <konstantinn@a-bb.net> wrote:
> >>> So, in summary, there is no way to predictably and efficiently tell
> Cassandra to get rid of all of the extra space it is using on disk?
> >>>
> >>> ----- Original Message -----
> >>> From: "Jeffrey Kesselman" <jeffpk@gmail.com>
> >>> To: user@cassandra.apache.org
> >>> Sent: Thursday, May 26, 2011 8:57:49 PM
> >>> Subject: Re: Forcing Cassandra to free up some space
> >>>
> >>> Which JVM?  Which collector?  There have been and continue to be many.
> >>>
> >>> Hotspot itself supports a number of different collectors with
> >>> different behaviors.   Many of them do not collect every candidate on
> >>> every gc, but merely the easiest ones to find.  This is why depending
> >>> on finalizers is a *bad* idea in java code.  They may well never get
> >>> run.  (Finalizer is one of a few features the Sun Java team always
> >>> regretted putting in Java to start with.  It has caused quite a few
> >>> application problems over the years)
> >>>
> >>> The really important thing is that NONE of these behaviors of the
> >>> colelctors are guaranteed by specification not to change from version
> >>> to version.  Basing your code on non-specified behaviors is a good way
> >>> to hit mysterious failures on updates.
> >>>
> >>> For instance, in the mid 90s, IBM had a mode of their Vm called
> >>> "infinite heap."  it *never* garbage collected, even if you called
> >>> System.gc.  Instead it just threw away address space and counted on
> >>> the total memory needs for the life of the program being less then the
> >>> total addressable space of the processor.
> >>>
> >>> It was *very* fast for certain kinds of applications.
> >>>
> >>> Far from being pedantic, not depending on undocumented behavior is
> >>> simply good engineering.
> >>>
> >>>
> >>> On Thu, May 26, 2011 at 4:51 PM, Jonathan Ellis <jbellis@gmail.com>
> wrote:
> >>>> I've read the relevant source. While you're pedantically correct re
> >>>> the spec, you're wrong as to what the JVM actually does.
> >>>>
> >>>> On Thu, May 26, 2011 at 3:14 PM, Jeffrey Kesselman <jeffpk@gmail.com>
> wrote:
> >>>>> Some references...
> >>>>>
> >>>>> "An object enters an unreachable state when no more strong references
> >>>>> to it exist. When an object is unreachable, it is a candidate for
> >>>>> collection. Note the wording: Just because an object is a candidate
> >>>>> for collection doesn't mean it will be immediately collected. The
JVM
> >>>>> is free to delay collection until there is an immediate need for
the
> >>>>> memory being consumed by the object."
> >>>>>
> >>>>>
> http://java.sun.com/docs/books/performance/1st_edition/html/JPAppGC.fm.html#998394
> >>>>>
> >>>>> and "Calling the gc method suggests that the Java Virtual Machine
> >>>>> expend effort toward recycling unused objects"
> >>>>>
> >>>>>
> http://download.oracle.com/javase/6/docs/api/java/lang/System.html#gc()
> >>>>>
> >>>>> It goes on to say that the VM will make a "best effort", but "best
> >>>>> effort" is *deliberately* left up to the definition of the gc
> >>>>> implementor.
> >>>>>
> >>>>> I guess you missed the many lectures I have given on this subject
> over
> >>>>> the years at Java One Conferences....
> >>>>>
> >>>>> On Thu, May 26, 2011 at 3:53 PM, Jonathan Ellis <jbellis@gmail.com>
> wrote:
> >>>>>> It's a common misunderstanding that system.gc is only a suggestion;
> on
> >>>>>> any VM you're likely to run Cassandra on, System.gc will actually
> >>>>>> invoke a full collection.
> >>>>>>
> >>>>>> On Thu, May 26, 2011 at 2:18 PM, Jeffrey Kesselman <
> jeffpk@gmail.com> wrote:
> >>>>>>> Actually this is no gaurantee.   Its a common misunderstanding
that
> >>>>>>> System.gc "forces" gc.  It does not. It is a suggestion
only. The
> vm always
> >>>>>>> has the option as to when and how much it gcs
> >>>>>>>
> >>>>>>> On May 26, 2011 2:51 PM, "Jonathan Ellis" <jbellis@gmail.com>
> wrote:
> >>>>>>>
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> --
> >>>>>> Jonathan Ellis
> >>>>>> Project Chair, Apache Cassandra
> >>>>>> co-founder of DataStax, the source for professional Cassandra
> support
> >>>>>> http://www.datastax.com
> >>>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>> --
> >>>>> It's always darkest just before you are eaten by a grue.
> >>>>>
> >>>>
> >>>>
> >>>>
> >>>> --
> >>>> Jonathan Ellis
> >>>> Project Chair, Apache Cassandra
> >>>> co-founder of DataStax, the source for professional Cassandra support
> >>>> http://www.datastax.com
> >>>>
> >>>
> >>>
> >>>
> >>> --
> >>> It's always darkest just before you are eaten by a grue.
> >>>
> >>
> >>
> >>
> >> --
> >> Jonathan Ellis
> >> Project Chair, Apache Cassandra
> >> co-founder of DataStax, the source for professional Cassandra support
> >> http://www.datastax.com
> >>
> >
> >
> >
> > --
> > It's always darkest just before you are eaten by a grue.
> >
>
>
>
> --
> Shotaro Kamio
>

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