On Tue, May 19, 2009 at 11:41 AM, Mark Martinec
<mark.martinec+ama...@ijs.si> wrote:
> Murilo,
>
>> I'd like to know how mail IDs are created by amavis. I mean I'd like
>> to have two 2 mysql servers replicating as master-master, so the field
>> msgs.mail_id cannot be duplicated.
>
> Entropy is being collected from passing mail and other system sources
> readily available to amavisd, then a mail_id is generated from this
> random source. Next the save_info_preliminary tries to insert
> a record into a table 'msgs' with this generated mail_id:
>
> 'ins_msg' =>
> 'INSERT INTO msgs (partition_tag, mail_id, secret_id, am_id,'.
> ' time_num, time_iso, sid, policy, client_addr, size, host)'.
> ' VALUES (?,?,?,?,?,?,?,?,?,?,?)',
>
> In an unlikely but possible case that the insertion fails, the probable
> cause is there was a clash with an existing mail_id, so another random
> mail_id is generated and the procedure repeats up to five times, which
> ensures that each mail_id in a database is unique within the range of
> records currently kept in a database (within the same partition_tag).
>
> # create unique mail_id and save preliminary info. to SQL (if enabled)
> for (my($attempt)=5;;) { # sanity limit on retries
> my($secret_id);
> ($mail_id,$secret_id) = generate_mail_id();
> $msginfo->secret_id($secret_id); $secret_id = '';
> $msginfo->mail_id($mail_id); # assign a long-term unique id to the msg
> if (!$sql_storage) {
> last; # no need to store and no way to check for uniqueness
> } else {
> # attempt to save a message placeholder to SQL, ensuring it is unique
> $which_section = 'sql-enter';
> $sql_storage->save_info_preliminary($conn,$msginfo) and last;
> if (--$attempt <= 0) {
> do_log(-2,"ERROR sql_storage: too many retries ".
> "on storing preliminary, info not saved");
> last;
> } else {
> snmp_count('GenMailIdRetries');
> do_log(2,"sql_storage: retrying preliminary, %d attempts remain",
> $attempt);
> sleep(int(1+rand(3)));
> add_entropy(Time::HiRes::gettimeofday,$$,$attempt);
> }
> }
> };
Thanks for explanation, Mark.
I think the probability on generating duplicated msgs.mail_id between
the 2 mysql servers (master-master) is amost impossible :-)
Thanks again.
--
Murilo Opsfelder Araújo
mopsfel...@gmail.com
{murilo,pan...@bsd.com.br
Don't learn to hack. Hack to learn.
BSD will never die.
"Tempo difícil esse em que estamos, em que é mais fácil quebrar um
átomo do que um preconceito." - Albert Einstein
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