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PMTA knowledge base›Metric§ 5.3

Connections

Current, peak and ceiling — three numbers at once

The number of simultaneous connections: now, the maximum and the allowed limit, in both directions.

What matters is not each value on its own but the distance between the current value and the ceiling. A node that hits the ceiling behaves differently from a node that does not reach it — and is treated differently.

🔴 The outgoing connection ceiling is cut by the license: on the standard one it is always two hundred, no matter what is written in the configuration.

The main trap is taking a snapshot for a history. The metric describes the moment of polling. Everything that happened between two measurements and managed to end will not get into either of them. For events there is accounting, for state — these numbers.
What the Hub does. It collects it partially: the poll puts only the current number of outgoing connections into the time series, while incoming connections, the ceiling and the peak value are shown live by the node monitor, without history.

🔴 The ceiling on outgoing connections is cut by the license: on the standard one it is always two hundred, whatever the configuration says.

Recommended values

What to compare with:

Value Compared with
current value the usual one for this node, not the neighboring one
peak the ceiling, if there is one
growth the growth rate, not the absolute number

Fleet nodes are not directly comparable: they have different hardware, different addresses and a different mix of receivers. It makes sense to compare a node with itself over time.

The comparison advice is ours. From the manual here come the metric’s composition and its units of measurement.
Example configuration
# the metric comes in the status snapshot
curl -s "http://127.0.0.1:8080/status?format=json"pmta show status
The highlighted line returns the snapshot as a structure — that is how the Hub’s polling reads it. The line below prints the same thing in the console.
yellow — — directive names, blue — blocks. They are highlighted the same way in the text of the card.
Compatibility
PowerMTA 6.0
described in the manual of this version · platform: any
The vendor does not state the first version for every directive — there is no note here. The name also appears in the 5.0 edition of the manual.
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Related entries

3 relations

Depends on

total-max-smtp-outGlobalOne of the configured limits reflected in this number. § 5.3The activation key is a prerequisite for installation, not a step after itThe license key also takes part in the ceiling — so the number is limited not only by the configuration. § 5.3

Works together with

Queue depthQueue depth without connections is the sign of a node that is not sending, rather than busy. inference

Referenced from

Throughput peaksConnections have their own maximum mark — together they show how close the node is to the ceiling. § 5.3The whole node state in one documentOne of the numbers in the response: how many connections are open at this moment. § 5.3The receiver went silent mid-conversationEach stalled attempt holds a place in this number for ten minutes. inferenceChange a sending address when messages are already queuedThe overlap lasts exactly as long as the connections opened before the reload live. inference

How to check on the node
The metric is viewed together with the neighboring ones — on its own any number means little:
pmta show status
pmta show queues --sort=rcpt --maxitems=20
The first prints all node metrics at once. The second breaks down by queue what the first gives as one number — and that is usually where you can see which queue made it up.
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What else to read

3 articles

◇What makes a virtual machine riskyRunning on a virtual machine is possible, but the manual does not recommend it without sufficient hardware and properly tuned hypervisor settings: under load the node may stop responding.◇A queue is a receiving server together with a sending addressThe engine groups messages by the “recipient domain plus sending address” pair: one domain from two addresses is two independent queues with their own counters, connections and mode.◇Recipients deferred after a temporary refusalA recipient to whom the receiver responded with 4xx moves into a separate waiting area with a per-receiver interval; two commands can release it early.

In the Hub
Cost of a mistake
safe: a wrong value breaks nothing
Scenarios
Capacity planning · Tune the pace for a provider · Untangle a stuck queue