Re: [Dovecot] The docs a re a bit weird on "Directory hashing"
On Fri, Aug 09, 2013 at 12:02:34AM +0300, Eliezer Croitoru wrote: > > > > I use: > > > > mail_home = /srv/mailstore/%256LRHu/%Ld/%Ln > "R" what for?? > I do understand a Lower case on the names and have seen the effect but > how would R be helpful?? > According to http://wiki2.dovecot.org/Variables "%H hash function is a bit bad if all the strings end with the same text, so if you're hashing usernames being in user@domain form, you probably want to reverse the username to get better hash value variety, e.g. %3RHu. " -jf
Re: [Dovecot] The docs a re a bit weird on "Directory hashing"
Hey, On 08/08/2013 10:29 AM, Jan-Frode Myklebust wrote: > On Thu, Aug 08, 2013 at 01:42:43AM +0300, Eliezer Croitoru wrote: >> >> And means a two layers cache of max 16 directories on the first layer >> and 256 directories on the second layer. >> The above allows millions of files storage and can benefit from all ext4 >> lower kernel levels of compatibly rather then do stuff on the user-land.. >> Since I am not 100% sure that the scheme I understood is indeed what I >> think I assume the above will need a small correction. > > I use: > > mail_home = /srv/mailstore/%256LRHu/%Ld/%Ln "R" what for?? I do understand a Lower case on the names and have seen the effect but how would R be helpful?? Eliezer > > which gives me 256 buckets containing domainname/username/, and the > buckets are a hash of Lowercase Reverse usernames. To get the same > layout as squid, I would try: > > mail_home = /srv/mailstore/%16LRHu/%256LRHu/%Lu > > Ref: http://wiki2.dovecot.org/Variables for variables and modifiers. > > BTW: I'm lowercasing everything, because I once got bitten by a variable > not being lowercased in one version, and suddenly this changing in > another version. It's probably redundant here -- but it was painful to > fix when it happened.. > > > -jf >
Re: [Dovecot] The docs a re a bit weird on "Directory hashing"
BTW. If you're using v2.2.3+ %N hash works better than the old %H hash. I updated http://wiki2.dovecot.org/Variables for it also. On 8.8.2013, at 1.42, Eliezer Croitoru wrote: > In squid we use a double layer of hashed directories on the FS to allow > storage of millions of files. > I was reading the "Directory hashing" section but never understood it.. > since it's written.. in a way I could not understand. > I am using this line: > mail_location = maildir:/home/vmail/%d/%n/Maildir/ > > and I want to migrate to a hash based directory scheme. > While trying to understand how that hash will work I stumbled a old > thread at: > http://www.dovecot.org/list/dovecot/2010-June/049695.html > there they used: > mail_location=maildir:/buzones/us.es/%1Hu/%2.1u/%n > > so I assume it should be used like that: > mail_location=maildir:/home/vmail/%H/%2.256Hn/%d_%n/Maildir/ > or: > mail_location=maildir:/home/vmail/%1Mu/%2.1Mu/%d_%n/Maildir/ > > It's a bit hard to think alone so I hope you can assist me. > > let say I want to follow the model of squid cache_dir which has: > cache_dir aufs /usr/local/squid/var/cache/squid 4 16 256 > > And means a two layers cache of max 16 directories on the first layer > and 256 directories on the second layer. > The above allows millions of files storage and can benefit from all ext4 > lower kernel levels of compatibly rather then do stuff on the user-land.. > Since I am not 100% sure that the scheme I understood is indeed what I > think I assume the above will need a small correction. > > Eliezer >
Re: [Dovecot] The docs a re a bit weird on "Directory hashing"
On Thu, Aug 08, 2013 at 01:42:43AM +0300, Eliezer Croitoru wrote: > > And means a two layers cache of max 16 directories on the first layer > and 256 directories on the second layer. > The above allows millions of files storage and can benefit from all ext4 > lower kernel levels of compatibly rather then do stuff on the user-land.. > Since I am not 100% sure that the scheme I understood is indeed what I > think I assume the above will need a small correction. I use: mail_home = /srv/mailstore/%256LRHu/%Ld/%Ln which gives me 256 buckets containing domainname/username/, and the buckets are a hash of Lowercase Reverse usernames. To get the same layout as squid, I would try: mail_home = /srv/mailstore/%16LRHu/%256LRHu/%Lu Ref: http://wiki2.dovecot.org/Variables for variables and modifiers. BTW: I'm lowercasing everything, because I once got bitten by a variable not being lowercased in one version, and suddenly this changing in another version. It's probably redundant here -- but it was painful to fix when it happened.. -jf
