How to Read a Varnish Histogram

graphvarnish

How is a varnishhist histogram/graph read? I understand that the x-axis is a log scale.

Specifically:

  • I see 9 "|"s or cache hits occur around y=1e-4, what does each "|" refer to? Page? File?

  • I see fewer hits to the left of these 9 "|"s and some to the right. What are those? Did they take longer (right) and shorter (left) time … ?

  • In the top, left what are 1:2? and n = 134

  • Also, I've noticed that the cache hits are always to the left of the cache misses, i.e., they are on the 1e-x side of things, while cache misses are under + exponent. What is the significance of that? Is that time, if so, time of what … ?

Many Thanks!

x-axis

1:2, n = 134                                                              hostname








                            #
                            #
                            #
                            #
                            #
                   |        #
                   |        #
                   |        #
                   |        #
                   |       ###
                   |       ###
                  ||       ###                              ##
                  |||      ###         ## #   #             ##
                  ||||     ####      #### ## ##  #          ###
+---------+---------+---------+---------+---------+---------+---------+---------+---------
|1e-6     |1e-5     |1e-4     |1e-3     |1e-2     |1e-1     |1e0      |1e1  |1e2

Best Answer

So the x-axis is the time it takes for the request to come into varnish and get sent back to the client. The |'s are the cache hits and the #'s are the misses. So you should see all the |'s on the left since that is a faster time.

So the left most numbers are faster.. the right most are slower..

now the 1:2 n= number.. Its numbers for the vertical scale and sample size. I wouldn't worry much about those.

But from that output.. you have a pretty fast cache going on.

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