Question about varnishstat

[Alexandre]

Hello,

I use varnishstat to watch hosts state, and I wonder what is the number 
18446744073709551615 ? Would you have any idea?

example:
---
varnishstat -1
.
.
.
VBE.web01(X.X.X.X,,1234).vcls              1          .   VCL references
VBE.web01_MC(X.X.X.X,,1234).happy  18446744073709551615          . 
Happy health probes
VBE.web02(X.X.X.X,,1234).vcls              1          .   VCL references
VBE.web02(X.X.X.X,,1234).happy  18446744073709551615          .   Happy 
health probes
VBE.web03(X.X.X.X,,1234).vcls              1          .   VCL references
VBE.web03(X.X.X.X,,1234).happy  18446744073709551615          .   Happy 
health probes
VBE.web04(X.X.X.X,,1234).vcls              1          .   VCL references
.
.
.
---


Thank you for your feedback.

Alex.