[Dovecot] mdbox compression

Patrick Domack patrickdk at patrickdk.com
Sat Feb 6 05:06:49 EET 2010

It's the real question of where the file is stored. For me, using nfs,  
using compression given me several times the performance of nfs, vs  
not using compression, for html files.

I would imagine the same benifits with email.

I would say something very close to the same with mdbox, if it's going  
over the network to a database server, compression will should clearly  
speed things up.

Now if your storing it on the local machine, then yes, compression  
will do nothing but slow things down, but can give you increased  
storage space.

Quoting Timo Sirainen <tss at iki.fi>:

> On 6.2.2010, at 3.23, Timo Sirainen wrote:
>> I was thinking that the compression would be delayed so that it  
>> would be done only after mdbox already decided that it wouldn't  
>> write any more data to it.
> Oh, and this is actually why I was thinking that maybe it could be a  
> good idea. If it's only done for older mails, they aren't accessed  
> that often. So maybe a hybrid solution would be a good idea for  
> mdbox users with alt storage:
>  * primary storage: SSD disks, mdbox file size = 100k, compress each  
> mail separately
>  * alt storage: spinning disks, mdbox file size = 2 MB, compress the  
> entire file
> Mails would be moved to alt storage after n days, perhaps  
> dynamically depending on available SSD disk space.
> SSDs can read data pretty fast though, so it would be nice to look  
> at some benchmarks that read tons of emails concurrently compressed  
> vs. uncompressed. Is the bottleneck CPU or I/O? Hmm. A quick test  
> with my Intel SSD shows that it can read 243 MB/s from a single  
> large file, while zlib input is only 100 MB/s with Macbook's one CPU  
> core. Faster CPUs and more cores would make zlib faster though.

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