Metrics in detail

This page describes the process characteristics and metrics that the N|Solid Runtime collects, and the few values that the N|Solid Console adds. Use it as a reference when you read nsolid.info() and nsolid.metrics() output, the nsolid-cli info and metrics commands, or data exported to OTLP and StatsD.

Process characteristics

The two primary data sets, info and metrics, contain values recorded live by the N|Solid Agent. They include data about the system hosting the process, the process as a whole, and each thread in the process.

Property	Description
app	The application name, from NSOLID_APP (or its alias NSOLID_APPNAME), the nsolid.app or name property in package.json, or nsolid.start(). Defaults to untitled application.
appVersion	The application version, from the version property in package.json or appVersion in nsolid.start().
execPath	The absolute path of the N|Solid executable running the application.
id	The unique N|Solid agent ID. Unique per N|Solid process.
main	The absolute path to the root module in the process's module tree.
iisNodeMain	(iisnode only, when iisNode is enabled) The absolute path to the real main script.
nodeEnv	The value of NODE_ENV, otherwise the env property in the nsolid section of package.json. Defaults to prod.
pid	The host system's process ID for the process. Unique per host.
processStart	The time the process started, in milliseconds since the epoch.
tags	The tags set with NSOLID_TAGS, the tags property in the nsolid section of package.json, or nsolid.start(). Up to 20 tags, each 2 to 140 bytes.
vulns	The number of known vulnerabilities found in the modules of the process. This value is added by the N|Solid Console.

Core library versions

The versions object in the info data lists the libraries built into Node.js core and added by N|Solid, with their versions. For example, from N|Solid 6.2.4 on Node.js 24:

versions: {
  acorn: '8.16.0',
  ada: '3.4.4',
  amaro: '1.1.8',
  ares: '1.34.6',
  brotli: '1.2.0',
  cldr: '48.0',
  curl: '8.18.0',
  grpc: '1.76.0',
  icu: '78.2',
  llhttp: '9.3.1',
  merve: '1.2.2',
  modules: '137',
  napi: '10',
  nbytes: '0.1.3',
  ncrypto: '0.0.1',
  nghttp2: '1.68.0',
  nlohmann: '3.12.0',
  node: '24.15.0',
  nsolid: '6.2.4',
  openssl: '3.5.5',
  opentelemetry: '1.23.0',
  protobuf: '6.33.2',
  simdjson: '4.5.0',
  simdutf: '6.4.0',
  sodium: '1.0.21',
  sqlite: '3.51.3',
  tz: '2026a',
  undici: '7.24.4',
  unicode: '17.0',
  uv: '1.51.0',
  uvwasi: '0.0.23',
  v8: '13.6.233.17-node.48',
  zlib: '1.3.1-e00f703',
  zmq: '4.3.5',
  zstd: '1.5.7'
}

The exact set of keys depends on the Node.js and N|Solid versions and the build.

System information

note

The host system may be physical hardware, a virtual machine, or a container.

Property	Description
arch	The host system's CPU architecture.
cpuCores	The host system's number of CPU cores (or hyperthreaded cores), as reported by the OS.
cpuModel	The host system's CPU model.
hostname	The host system's configured hostname, unless overridden with NSOLID_HOSTNAME or the hostname property in the nsolid section of package.json.
kernelVersion	The Linux kernel version encoded as a number. 0 on other platforms.
platform	The host system's operating system platform.
totalMem	The host system's total memory, in bytes. This is the host's memory, not a container memory limit. Reported in the info data and, starting with N|Solid 6.3.0, also in the metrics.

System data

Property	Description
freeMem	The host system's amount of free (unused) memory, in bytes.
load1m	The average number of processes on the host that were running or waiting for CPU time over the past minute.
load5m	... over the past 5 minutes.
load15m	... over the past 15 minutes.
systemUptime	The host system's uptime, in seconds.

note

These numbers aren't correlated with the core that the process or its threads run on.

General process stats and information

Property	Description
timestamp	When the metrics were collected, in milliseconds since the epoch.
blockInputOpCount	The number of file system input operations performed by the process.
blockOutputOpCount	The number of file system output operations performed by the process.
cpuSystemPercent	The percentage of CPU the process used in system calls, for example 4.1.
cpuUserPercent	The percentage of CPU the process used in user code, for example 7.4.
cpuPercent	The percentage of CPU used by the process, for example 11.5. Equal to user plus system. It's measured against a single core, so values above 100 are possible for multi-threaded workloads.
cpu	Legacy alias of cpuPercent.
ctxSwitchInvoluntaryCount	The number of involuntary context switches away from the process, for example because a higher-priority process needed time or the process used up its time slice.
ctxSwitchVoluntaryCount	The number of voluntary context switches away from the process, where the process yielded before its time slice ended, usually to wait for an I/O resource.
pageFaultHardCount	The number of hard page faults triggered by the process: the process tried to read from memory, but the page had been moved to disk. These can be costly for performance.
pageFaultSoftCount	The number of soft page faults (page reclaims) triggered by the process: the page was still in memory but had to be remapped. Not a great cause for concern.
title	The current system title of the process.
uptime	The process uptime, in seconds.
user	The system user currently running the process. Reflects changes made at runtime.
rss	The resident set size (RSS): the total memory used by the process. All other active memory sections are subsets of RSS. If this value grows continually and never stabilizes, you likely have a memory leak.

Legacy POSIX process statistics

These POSIX values are considered legacy but are kept for potential future use.

Property	Description
ipcReceivedCount	The number of IPC messages received by the process. Not used on modern platforms.
ipcSentCount	The number of IPC messages sent by the process. Not used on modern platforms.
signalCount	The number of signals received by the process. Not used on modern platforms.
swapCount	The number of times the process was swapped out of memory. Not used on modern platforms.

Per-thread metrics

To support Node.js worker threads, the metrics that relate to a specific thread are reported separately for the main thread and for each worker thread.

Property	Description
threadName	The name of the thread, if set with nsolid.setThreadName().
threadId	The thread's ID. The main thread is 0.

JavaScript memory stats

rss isn't specific to a thread, so it's listed with the process stats. Each thread's heapTotal and externalMem are subsets of the process's rss.

Property	Description
totalAvailableSize	The remaining amount of memory the thread's heap can allocate before reaching the maximum heap size, in bytes.
totalHeapSizeExecutable	The total amount of executable memory (containing code instructions) allocated in the thread's heap, in bytes.
totalPhysicalSize	The amount of physical memory currently committed for the thread's heap, in bytes.
heapSizeLimit	The maximum size of the thread's JavaScript heap, in bytes. If the allocator requests memory beyond this limit, V8 terminates the process with an allocation failure.
heapTotal	The thread's total allocated JavaScript heap size, in bytes. Includes the used portion (heapUsed) and spare memory. When heapUsed gets close to heapTotal, V8 allocates more memory; as the garbage collector frees objects, it can shrink.
heapUsed	The thread's used JavaScript heap size, in bytes: the memory storing all JavaScript objects and values. A key value to watch for memory leaks.
externalMem	The thread's memory allocated by Node.js outside of V8's heap but referenced from the heap, in bytes. This is where Buffers and native addon memory live. It may exceed RSS if large Buffers are allocated but not yet backed by physical memory.
numberOfNativeContexts	The number of attached contexts, typically created with the vm module to create additional V8 memory sandboxes.
numberOfDetachedContexts	The number of detached contexts that still hold memory and aren't being garbage collected.
mallocedMemory	The amount of memory currently allocated with malloc by V8, in bytes.
peakMallocedMemory	The largest amount of memory allocated with malloc by V8 over the life of the thread, in bytes.

Node.js event loop stats

tip

To learn more about event loop utilization, read the event loop utilization blog post.

Property	Description
loopAvgTasks	Legacy metric kept for backward compatibility. Don't rely on it.
loopEstimatedLag	The estimated time an I/O response may have to wait on the thread's event loop, in milliseconds.
loopIdlePercent	The percentage of time the event loop is waiting (idle) for I/O or timers.
loopTotalCount	The cumulative count of all event loop iterations. Legacy name for loopIterations.
loopIterations	The total number of event loop iterations since the thread started.
loopIterWithEvents	The total number of event loop iterations since the thread started that had events to handle.
loopIdleTime	The total time the event loop has spent idle since the thread started, in nanoseconds.
loopUtilization	The ratio of time the event loop spends processing events rather than being idle. When this number grows, you may start to see latency spikes.
eventsProcessed	The total number of events processed by the event loop since the thread started.
eventsWaiting	The cumulative number of events that were already waiting in the queue when the event provider was polled. A growing rate indicates event loop lag.
providerDelay	The cumulative estimated time events spent waiting in the event queue before being received by the event loop, in nanoseconds.
processingDelay	The cumulative estimated time events waited, after being received by the event loop, before being processed, in nanoseconds.
res5s	A moving average of the event loop's "responsiveness" over the past 5 seconds: the ratio of estimated event delay to processing time.
res1m	... over the past minute.
res5m	... over the past 5 minutes.
res15m	... over the past 15 minutes.

JavaScript garbage collection stats

Property	Description
gcCount	The total number of garbage collections of any type done by the thread.
gcDurUs99Ptile	The 99th percentile duration of the thread's garbage collections, in microseconds. This is the cutoff for the slowest 1% of GC events.
gcDurUsMedian	The median duration of the thread's garbage collections, in microseconds.
gcForcedCount	The number of externally forced garbage collections on the thread, for example triggered by taking a heap snapshot.
gcFullCount	The number of garbage collections on the thread that collected all available garbage. Usually only seen when heapTotal is approaching heapSizeLimit.
gcMajorCount	The number of major garbage collections on the thread, such as a mark-sweep.

HTTP and DNS stats

Property	Description
dnsCount	The total number of DNS lookups performed since the thread started.
dnsMedian	The median duration of DNS lookups, in milliseconds.
dns99Ptile	The 99th percentile duration of DNS lookups, in milliseconds.
httpClientCount	The total number of outgoing HTTP(S) client requests performed.
httpClientAbortCount	The total number of outgoing HTTP(S) client requests canceled due to inactivity or by calling abort().
httpClientMedian	The median duration of completed outgoing HTTP(S) client requests, in milliseconds.
httpClient99Ptile	The 99th percentile duration of completed outgoing HTTP(S) client requests, in milliseconds.
httpServerCount	The total number of incoming HTTP(S) requests served.
httpServerAbortCount	The total number of incoming HTTP(S) requests that were aborted.
httpServerMedian	The median duration of completed incoming HTTP(S) requests, in milliseconds.
httpServer99Ptile	The 99th percentile duration of completed incoming HTTP(S) requests, in milliseconds. These are the slowest 1% of requests handled by your HTTP server.

I/O primitives

As your application creates and uses I/O primitives, these metrics track the cumulative numbers over the life of the thread. They're good indicators of activity and can reveal memory leaks caused by I/O resources that aren't closed.

Property	Description
activeHandles	The number of active libuv handles: long-lived asynchronous resources such as open sockets, servers, timers, and child processes.
activeRequests	The number of active libuv requests: short-lived operations such as file system calls, DNS lookups, and socket writes.
pipeServerCreatedCount	The total number of server objects created using named pipes.
pipeServerDestroyedCount	The total number of pipe server objects torn down.
pipeSocketCreatedCount	The total number of pipe socket objects created.
pipeSocketDestroyedCount	The total number of pipe socket objects torn down.
tcpServerCreatedCount	The total number of TCP server objects created.
tcpServerDestroyedCount	The total number of TCP server objects torn down.
tcpSocketCreatedCount	The total number of TCP socket objects created.
tcpSocketDestroyedCount	The total number of TCP socket objects torn down.
udpSocketCreatedCount	The total number of UDP socket objects created.
udpSocketDestroyedCount	The total number of UDP socket objects torn down.
promiseCreatedCount	The total number of promises created. Requires promise tracking (see the note below).
promiseResolvedCount	The total number of promises resolved. Requires promise tracking.
fsHandlesOpenedCount	The total number of file system handles opened.
fsHandlesClosedCount	The total number of file system handles closed.

note

The N|Solid Runtime doesn't track promises by default. To enable it, set NSOLID_PROMISE_TRACKING=1 or set promiseTracking to true in your N|Solid configuration. You can also enable it from the N|Solid Console.