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From <>
Subject RE: Removal of old data files
Date Tue, 27 Sep 2011 21:16:34 GMT

Now, we use TTL of 12 hours and GC grace period of 8 hours for encouraging Cassandra to remove
old data/files more aggressively.  

Cassandra do remove fair amount of old data files. 
Cassandra tends to removed 4 out of every 5 files. 
I notice it because data file has a sequence number as a part of name.

I also noticed when Cassandra generated *-Compacted file it generated 4 file at a time. 
They have consecutive numbers as file name, but skip one number from the previous group of
The one missing is the file that is failed to be removed in the end and stays forever. 

I looked at the Keys in an index file that failed to be removed.  If I make query of any of
keys, Cassandra indicates that there is not data, which is correct because these files are
older than 24 hours.  All the data must be obsolete due to TTL.     
I am wondering why Cassandra does not remove all data file whose time stamp is much older
than TTL + grace period. 

Does anybody have similar experience ? 

Yuki Watanabe

-----Original Message-----
From: Watanabe, Hiroyuki: IT (NYK) 
Sent: Friday, September 02, 2011 9:01 AM
Subject: RE: Removal of old data files

I see. Thank you for helpful information 


-----Original Message-----
From: Sylvain Lebresne []
Sent: Friday, September 02, 2011 3:40 AM
Subject: Re: Removal of old data files

On Fri, Sep 2, 2011 at 12:11 AM,  <> wrote:
> Yes, I see files with name like
>     Orders-g-6517-Compacted
> However, all of those file have a size of 0.
> Starting from Monday to Thurseday we have 5642 files for -Data.db, 
> -Filter.db and Statistics.db and only 128 -Compacted files.
> and all of -Compacted file has size of 0.
> Is this normal, or we are doing something wrong?

You are not doing something wrong. The -Compacted files are just marker, to indicate that
the -Data file corresponding (with the same number) are, in fact, compacted and will eventually
be removed. So those files will always have a size of 0.


> yuki
> ________________________________
> From: aaron morton []
> Sent: Thursday, August 25, 2011 6:13 PM
> To:
> Subject: Re: Removal of old data files
> If cassandra does not have enough disk space to create a new file it 
> will provoke a JVM GC which should result in compacted SStables that 
> are no longer needed been deleted. Otherwise they are deleted at some 
> time in the future.
> Compacted SSTables have a file written out with a "compacted" extension.
> Do you see compacted sstables in the data directory?
> Cheers.
> -----------------
> Aaron Morton
> Freelance Cassandra Developer
> @aaronmorton
> On 26/08/2011, at 2:29 AM, yuki watanabe wrote:
> We are using Cassandra 0.8.0 with 8 node ring and only one CF.
> Every column has TTL of 86400 (24 hours). we also set 'GC grace 
> second' to 43200
> (12 hours).  We have to store massive amount of data for one day now 
> and eventually for five days if we get more disk space.
> Even for one day, we do run out disk space in a busy day.
> We run nodetool compact command at night or as necessary then we run 
> GC from jconsole. We observed that  GC did remove files but not 
> necessarily oldest ones.
> Data files from more than 36 hours ago and quite often three days ago 
> are still there.
> Does this behavior expected or we need adjust some other parameters?
> Yuki Watanabe
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