Large Periodic Plots

George Snyder  –  January 12, 2007
Plotting a large data set in a compact format can reveal trends visually which might be hard to detect algorithmically.  The examples here show ping response time from several servers over a period of approximately two years.  Each pixel represents one minute, so each plot displays about a million data points.  A number of trends are readily apparent, and subtler ones can be detected.  They are described in annotations on the plots.

Response times are classified as follows:

Fast Color
Fast 0 - 10 ms

Good color

Good 10 - 60 ms

Fair color

Fair 60 - 90 ms

Slow color

Slow Over 90 ms

No Response color

No Response The host was down or not responding to pings, or the network was down

Off-line color

No Response The measuring host (laptop) was off the network (very dark gray)

No Data color

No Data The measuring host was down or was not taking data (black)

Recommendations for Viewing

The plots are wide; scroll them horizontally.  Use View > Full Screen (commonly [F11]) in your browser to maximize viewing area.  See the bottom of each page for annotation and zooming options.  Zoom out (Fit All) to compare long term trends on all servers over the full two years.  Zoom in (100%) to see shorter term trends and to read the annotations.

Plots by Day      

These plots emphasize trends which occur at consistent times of the day.  Each plot is one day across, approximately two years high.  Each row of pixels is one day (1440 minutes).  Each hour of the day is a column 60 pixels wide, and is marked with grid points.  Each month is a row 31 pixels high, also marked with grid points.

Plots by Week   

These plots emphasize trends which occur on consistent days of the week.  They show the same data, but grouped into blocks of one day each.  Each day has one row of pixels per hour.  The days are in columns of one week. 

Machine Descriptions

Measuring Host (Badger)
Littleton, MA; later Andover, MA
A desktop PC running Windows 2000.  "No Data" (black) areas are due to the measuring host being down, in all known cases.
Mail Server
Littleton, MA
Generally fast response, with long-term degradations and improvements.
SMB Authorization Server
Fort Collins, CO
Generally fair response, with a period of slow response.
Roseville Server
Roseville, CA
Generally slow response, with occasional improvements.
Web Proxy Server
Atlanta, GA
Consistently good response, with short scattered degradations.
The desktop PC listed above, as measured from a laptop PC running Windows XP Pro.  In this plot, "No Response" is shown as dark gray rather than red, because it usually means the laptop was disconnected from the network.

Plot Generation

The data was gathered by a continuously running Perl script for each server.  The plots were produced using Perl and Java.  The viewing pages use JavaScript.