On 2012-10-26 00:15, Ben Morrow wrote:
At 10AM +0300 on 25/10/12 you (Robert JR) wrote:
Stan, sorry but you didnot understand my question at all, dovecot in
this case is reading the mailbox file while user downloading the
mail
and not WRITING. only postfix write when a mail arrives and DOVECOT
only read the mail. And even if both write to the file, I have
already
set the locking option of both to FCNTL so no problem should happen.
My
question is postfix locking option is = FCNTL, DOTLOCK , and dovecot
=
FCNTL, if postfix find a file already FCNTL, why it dotlock the file
5
secs then remove the dotlock and say resource unaviable?
As Stan said earlier, this is a Postfix question. The rule for
dotlocking is that you must create the .lock *before* opening the
file,
in case whoever has it locked will be replacing the file altogether;
but
with fcntl locking you must acquire the lock *after* opening the
file,
since that's the way the syscall works. This means that if Postfix is
going to use both forms of lock, it has to acquire a dotlock before
it
can look for a fcntl lock.
In other words: the methods in mailbox_delivery_lock are *not* tried
in
order, because they can't be. Dotlock is always tried first.
You should have compatible locking settings for all your programs
accessing your mboxes. If Postfix is using dotlock, Dovecot should be
using dotlock as well. If you don't have any local programs (mail
clients, for instance) which require dotlocks, you should probably
change Postfix to just use fcntl locks.
Ben
Thanks Ben for your valuable support and detailed explanation .. but
according to your explanation dovecot documentation contains wrong
explanation to the dotlock and that's why i was confused.
it is written as follow
**
If multiple lock methods are used, which is usually the case since
dotlocks aren't typically used for read locking, the order in which the
locking is done is important. Consider if two programs were running at
the same time, both use dotlock and fcntl locking but in different
order:
Program A: fcntl locks the mbox
Program B at the same time: dotlocks the mbox
Program A continues: tries to dotlock the mbox, but since it's already
dotlocked by B, it starts waiting
Program B continues: tries to fcntl lock the mbox, but since it's
already fcntl locked by A, it starts waiting
Now both of them are waiting for each others locks. Finally after a
couple of minutes they time out and fail the operation.
**
So this means that the documentation as mentioned above is wrong and
dotlock is always first even if the order is different ..
Anyway i have sent this question to postfix maillist and i will wait
their reply .
Thanks again
Robert.
