Demo
Demo

Knowledge base

PMTA knowledge base›Metric§ 5.3

Name cache

Domain Names
How many names are remembered and how many queries are pending

The number of names in the cache and the number of queries awaiting an answer; separately — active queries.

A growing number of hanging queries is the earliest sign that the resolver is not coping. Earlier than delivery failures appear: those will come when queries start to time out.

⚠️ We have no threshold for it: the number is visible, but nobody looks at it. And this is the only metric that warns about resolver failures in advance.

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 shows it live: the node monitor displays the number of cached names and queries in progress, but the poll does not put them into the time series.

⚠️ We have no threshold for it: the number is visible, but nobody looks at it. And this is the only metric that warns about resolver failures in advance.

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.
⇄

Related entries

2 relations

Works together with

The name lookup did not complete — and no conclusion is drawnPending queries that never got a response are exactly what becomes this failure. § 5.8

Where you can see it

The node needs a resolver that does all the work itselfThe numeric sign of the qualitative requirement written in the node preparation. § 4.2.3

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.
◇

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.◇The node needs a resolver that does all the work itselfThe engine requires recursive name resolution; a resolver that answers with a referral to another server forces the query to be repeated and triggers a log warning.◇The activation key is a prerequisite for installation, not a step after itWithout an activation key from SparkPost support the engine neither installs nor runs, and the license tier sets the outbound connection ceiling: on Standard everything above 200 is ignored.

In the Hub
Cost of a mistake
safe: a wrong value breaks nothing
Scenarios
Prepare a node for sending · Untangle a stuck queue