JVM Statistics Monitoring Tool (jstat) Command Usage Guide

JVM Statistics Monitoring Tool (jstat) is a command used to monitor runtime information of a Java virtual machine, displaying data such as class loading, memory usage, garbage collection, and JIT compilation.

Command format

jstat [options] VMID [interval] [count]

Parameters

[options] : operation parameters, commonly -gcutil to view GC status. VMID : local JVM process ID (the Java process number). [interval] : time interval between consecutive outputs, in seconds or milliseconds. [count] : number of consecutive outputs; if omitted, it prints indefinitely.

Option Overview

Option Details

-class (monitor class loading/unloading counts, total space, and time spent)

Loaded: number of loaded classes Bytes: size of loaded class bytes Unloaded: number of unloaded classes Bytes: size of unloaded class bytes Time: loading time

-compiler (output JIT compilation statistics such as number of compiled methods and time spent)

Compiled: number of compiled methods Failed: number of compilation failures Invalid: number of invalid compilations Time: compilation time FailedType: type of failure FailedMethod: fully qualified name of the failed method

-gc (statistics of garbage‑collection heap behavior; commonly used)

C = Capacity (total), U = Used (currently used). The table lists metrics such as S0C, S0U, S1C, S1U, EC, EU, OC, OU, PC, PU, YGC, YGCT, FGC, FGCT, GCT, etc.

Example: jstat -gc 4513 2000 2 prints GC statistics of process 4513 every 2000 ms, two times.

-gccapacity (same as -gc but also shows the maximum and minimum space used by each heap region)

NGCMN/NGCMX: min/max space of young generation OGCMN/OGCMX: min/max space of old generation PGCMN/PGCMX: min/max space of perm generation

-gcutil (same as -gc but shows used space as a percentage of total)

-gccause (GC statistics overview like -gcutil plus reasons for the last two GC events)

LGCC: reason for the most recent GC GCC: reason for the current GC

-gcnew (statistics of young‑generation behavior)

TT: Tenuring threshold MTT: maximum tenuring threshold DSS: size of survivor space (KB)

-gcnewcapacity (statistics of young‑generation memory space)

NGC: current young‑generation capacity (KB) S0CMX: maximum S0 space (KB) S0C: current S0 space (KB) ECMX: maximum Eden space (KB) EC: current Eden space (KB)

-gcold (statistics of old‑generation behavior)

-gcoldcapacity (statistics of old‑generation memory space)

-gcpermcapacity (statistics of permanent generation memory space)

-printcompilation (statistics of HotSpot compiled methods)

Compiled: number of compiled tasks executed Size: byte size of method bytecode Type: compilation type Method: class name (using '/' instead of '.') and method name, consistent with HotSpot -XX:+PrintCompilation output.

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