[Dovecot] pop3_lock_session and NFS
Hello,
I need an advice about POP3 and NFS with Dovecot 1.0 (as 1.1 is still tagged beta) .
I currently have all messages and indexes under a NFS partition . I thus turned cache off using actimeo=0 . Of course, my current architecture does not allow me to keep the same user on the same dovecot server.
Now, I have some NFS issues with high percentages of getattr() . If I understood well, the cache must be disabled, because of the case of 2 differents computers could log on the same time and mess up the index file .
If I use the directive pop3_lock_session and enable it, that should block conccurent pop3 access using a lock file . Can I consider it safe enough to turn on the NFS cache (ie removing actimeo=0) ?
Thanks in advance
Salim
Ps: For you info, we use dovecot here for a big cable broadband ISP, with 2,000,000 mailboxes using 30 dovecot POP3 servers,10 dovecot proxy servers and we are really happy with your nice software, we expect a lot from 1.1 .
On Wed, 2007-11-21 at 22:08 +0100, salimlist@sdv.fr wrote:
If I use the directive pop3_lock_session and enable it, that should block conccurent pop3 access using a lock file . Can I consider it safe enough to turn on the NFS cache (ie removing actimeo=0) ?
What OS do you use? I guess with pop3_lock_session=yes you should be somewhat safe with Linux/Solaris, but not entirely. If you use BSDs then locking doesn't work correctly.
I've been trying hard to figure out how NFS caches for for the last week and I think today's the first day I've finally understood it all correctly. :) I've been writing about those issues to http://iki.fi/tss/nfs-coding-howto.html
With my newly found understanding even actimeo=0 isn't enough with v1.0, at least if your NFS server doesn't support nano/microsecond resolution for timestamps. And I should still do a few changes to v1.1's NFS cache flushing..
At 22/11/2007 04:19, Timo Sirainen wrote:
On Wed, 2007-11-21 at 22:08 +0100, salimlist@sdv.fr wrote:
If I use the directive pop3_lock_session and enable it, that should block conccurent pop3 access using a lock file . Can I consider it safe enough to turn on the NFS cache (ie removing actimeo=0) ?
What OS do you use? I guess with pop3_lock_session=yes you should be somewhat safe with Linux/Solaris, but not entirely. If you use BSDs then locking doesn't work correctly.
I use Linux kernel 2.6.16.20 .
I've been trying hard to figure out how NFS caches for for the last week and I think today's the first day I've finally understood it all correctly. :) I've been writing about those issues to http://iki.fi/tss/nfs-coding-howto.html
That a very useful document, I tryed on my side too to understand the linux cache, thanks !
With my newly found understanding even actimeo=0 isn't enough with v1.0, at least if your NFS server doesn't support nano/microsecond resolution for timestamps. And I should still do a few changes to v1.1's NFS cache flushing..
I think I will turn pop3_lock_session to on and enable the NFS cache to see the real benefits in term of NFS performance. If you are interested with results, let me know .
I will also count the # of occurences of bad index files found in the log to see how safe that configuration is.
Thanks a lot for your help .
Salim
participants (2)
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salimlist＠sdv.fr
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Timo Sirainen