Why is "MC" greater than "MU" when I use the jstat command?

Question

Why is MC greater than mu when I use the jstat command?, eg.

$./jstat -gc 2820
 S0C    S1C    S0U    S1U      EC       EU        OC         OU       MC     MU    CCSC   CCSU   YGC     YGCT    FGC    FGCT     GCT
174720.0 174720.0  0.0   64633.5 1747712.0 1449365.0 2097152.0   263408.2  304768.0 299380.5 37760.0 36489.7     13    1.766   0      0.000    1.766

It says that MC is 304768.0 while MU is 299380.5.

Answer 1

The documentation says that

• MC: Metaspace capacity (kB).
• MU: Metacspace utilization (kB).

So MC is the total capacity and MU is how much of MC you are currently using. Hence it only makes sense that MC is greater (equals) MU.

The opposite would be weird, but not MC > MU.

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In your case you have a metaspace capacity of around 304 MB and currently use 299 MB of that.

Answer 2

1. MC is Metaspace size
2. MU is Metaspace used size