please unsubscribe

[Vivek Mishra <vi...@impetus.co.in>]

From: Sam Overton [mailto:soverton@acunu.com]
Sent: Friday, September 23, 2011 3:09 PM
To: user@cassandra.apache.org
Subject: Re: LevelDB type compaction


On 17 September 2011 00:58, mcasandra <mo...@gmail.com>> wrote:
>
>> and updates could be scattered all over
>> before compaction?
>
> No, updates to a given row will be still be in a single sstable.
Can you please explain little more? You mean that if Level 1 file contains
range from 1-100 all the updates would still go in that file?

No, sstables are never written to. All updates go to a memtable, which is then flushed to a Level0 sstable. Compaction then causes promotion of updates to gradually higher levels.

The link on leveldb says:

> The compaction picks a file from level L and all overlapping files from
> the next level L+1

If all updates go in the same sstables then how do overlapping files get
generated. By overlapping I am assuming it means new or updated value for a
given key exists in multiple files?

Overlapping refers to the range of keys. The key ranges contained within the files in any given level represent a set of disjoint intervals (when level >=1). For Level0, the files may contain overlapping ranges.

Thanks for the explanation

Disclaimer: I haven't read the code, this is just my understanding from reading the docs.


Sam Overton
Acunu | http://www.acunu.com<http://www.acunu.com/> | @acunu

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Re: please unsubscribe

[Jeremy Hanna <je...@gmail.com>]

Vivek - to unsubscribe, look at this link: http://wiki.apache.org/cassandra/FAQ#unsubscribe
On Sep 23, 2011, at 4:40 AM, Vivek Mishra wrote:

>  
>  
> From: Sam Overton [mailto:soverton@acunu.com] 
> Sent: Friday, September 23, 2011 3:09 PM
> To: user@cassandra.apache.org
> Subject: Re: LevelDB type compaction
>  
>  
> On 17 September 2011 00:58, mcasandra <mo...@gmail.com> wrote:
> >
> >> and updates could be scattered all over
> >> before compaction?
> >
> > No, updates to a given row will be still be in a single sstable.
> 
> Can you please explain little more? You mean that if Level 1 file contains
> range from 1-100 all the updates would still go in that file?
>  
> No, sstables are never written to. All updates go to a memtable, which is then flushed to a Level0 sstable. Compaction then causes promotion of updates to gradually higher levels.
>  
> The link on leveldb says:
> 
> > The compaction picks a file from level L and all overlapping files from
> > the next level L+1
> 
> If all updates go in the same sstables then how do overlapping files get
> generated. By overlapping I am assuming it means new or updated value for a
> given key exists in multiple files?
>  
> Overlapping refers to the range of keys. The key ranges contained within the files in any given level represent a set of disjoint intervals (when level >=1). For Level0, the files may contain overlapping ranges.
>  
> Thanks for the explanation
>  
> Disclaimer: I haven't read the code, this is just my understanding from reading the docs.
>  
>  
> Sam Overton
> Acunu | http://www.acunu.com | @acunu
> 
> 
> Hear Impetus’ expert talk about Next Gen Big Data Architectures at Strata Conference, NYC on Sept 22-23. http://t.co/GD2L0N8g. Listen to recording of Impetus Webinar ‘Utilizing Cloud- based Services for Enterprise Mobility’ at http://bit.ly/pqV4vj. 
> 
> Click http://www.impetus.com to know more. Follow us on www.twitter.com/impetuscalling 
> 
> 
> NOTE: This message may contain information that is confidential, proprietary, privileged or otherwise protected by law. The message is intended solely for the named addressee. If received in error, please destroy and notify the sender. Any use of this email is prohibited when received in error. Impetus does not represent, warrant and/or guarantee, that the integrity of this communication has been maintained nor that the communication is free of errors, virus, interception or interference.