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Diffstat (limited to 'doc/doc-docbook/spec.xfpt')
| -rw-r--r-- | doc/doc-docbook/spec.xfpt | 39 |
1 files changed, 38 insertions, 1 deletions
diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index ed3533a0c..f9a8efa98 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -1575,7 +1575,7 @@ If a host is unreachable for a period of time, a number of messages may be waiting for it by the time it recovers, and sending them in a single SMTP connection is clearly beneficial. Whenever a delivery to a remote host is deferred, -.cindex "hints database" +.cindex "hints database" "deferred deliveries" Exim makes a note in its hints database, and whenever a successful SMTP delivery has happened, it looks to see if any other messages are waiting for the same host. If any are found, they are sent over the same SMTP @@ -20539,6 +20539,32 @@ transport, the &[initgroups()]& function is called when running the transport to ensure that any additional groups associated with the uid are set up. +.new +.option max_parallel transports integer&!! unset +.cindex limit "transport parallelism" +.cindex transport "parallel processes" +.cindex transport "concurrency limit" +.cindex "delivery" "parallelism for transport" +If this option is set and expands to an integer greater than zero +it limits the number of concurrent runs of the transport. +The control does not apply to shadow transports. + +.cindex "hints database" "transport concurrency control" +Exim implements this control by means of a hints database in which a record is +incremented whenever a transport process is beaing created. The record +is decremented and possibly removed when the process terminates. +Obviously there is scope for +records to get left lying around if there is a system or program crash. To +guard against this, Exim ignores any records that are more than six hours old. + +If you use this option, you should also arrange to delete the +relevant hints database whenever your system reboots. The names of the files +start with &_misc_& and they are kept in the &_spool/db_& directory. There +may be one or two files, depending on the type of DBM in use. The same files +are used for ETRN and smtp transport serialization. +.wen + + .option message_size_limit transports string&!! 0 .cindex "limit" "message size per transport" .cindex "size" "of message, limit" @@ -22436,6 +22462,10 @@ If two messages arrive at almost the same time, and both are routed to a pipe delivery, the two pipe transports may be run concurrently. You must ensure that any pipe commands you set up are robust against this happening. If the commands write to a file, the &%exim_lock%& utility might be of use. +.new +Alternatively the &%max_parallel%& option could be used with a value +of "1" to enforce serialization. +.wen @@ -23618,6 +23648,10 @@ start with &_misc_& and they are kept in the &_spool/db_& directory. There may be one or two files, depending on the type of DBM in use. The same files are used for ETRN serialization. +.new +See also the &%max_parallel%& generic transport option. +.wen + .option size_addition smtp integer 1024 .cindex "SMTP" "SIZE" @@ -36265,6 +36299,9 @@ Serializing ETRN runs (when &%smtp_etrn_serialize%& is set) .next Serializing delivery to a specific host (when &%serialize_hosts%& is set in an &(smtp)& transport) +.next +Limiting the concurrency of specific transports (when &%max_parallel%& is set +in a transport) .endlist |