How to get heap usage using jstat?

Question

I\'m running jstat -gc (from OpenJDK):

# jstat -gc 1
 S0C    S1C    S0U    S1U      EC       EU        OC         OU       MC     MU    CCSC   CC         


        

Answer 1

See https://docs.oracle.com/javase/8/docs/technotes/tools/unix/jstat.html for general reference.

Current heap size would be the sum of all the fields that end with "C" - S0C, S1C, EC, OC (except for Metaspace which is the fields that start with "M")

Used heap would be the sum of all the fields that end with "U" - S0U, S1U, EU, OU (again, except metaspace).

Note that the "C" values (current) are greater than or equal to "U" values (actually used).

To get maximum values run jstat with the -gccapacity flag and add up all the fields that end with "MX" (NGCMX, OGCMX, ... except for MCMX which is metaspace).