MySQL Bugs: #41232: Graphs incorrect for data that doesn't change (acts like *no* data)

Bug #41232	Graphs incorrect for data that doesn't change (acts like no data)
Submitted:	4 Dec 2008 15:25	Modified:	2 Mar 2009 17:06
Reporter:	Mark Leith	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Enterprise Monitor: Server	Severity:	S3 (Non-critical)
Version:	2.0.0.7105	OS:	Any
Assigned to:	Darren Oldag	CPU Architecture:	Any
Tags:	Graphs

Description:
The Hit Ratios graphs shows gaps in it, when there has not been any activity on the things that are being monitored. For instance if you do not use MyISAM tables, then no Key Cache hit ratio series is plotted, even though the variables are still being collected. 

How to repeat:
o Set up an idle instance
o Do not connect to it, or issue queries against the caches for a period of time
o Maybe then issue one query that hits the innodb buffer pool/key cache
o And another that hits the query cache
o Run nothing again for a period of time
o Note that you get disjoined plots, even though data is still being collected

Suggested fix:
Not sure! Would be nice to distinguish between "no change" on the graphs and "no data was collected".

pushed into trunk, awaiting 2.1 build and test.

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when the fix for "don't draw lines when there is no data" was put in,
a regression was introduced that drew gaps when there WAS data... but it
was not renderable.  specifically, the 0/0 ratios case (no activity).

we want a continuous line there, but ignore that specifc time data point.
but we still want to draw gaps when there really is NO data.

the data model previously only sent up to the renderer the 'valid' points,
so there was not enough info to draw it correctly.  this was changed
so that, even if it is bad data, the time entries are now sent up.

this makes it fully the 'rendering' phase's responsibility to handle
the rendering (go figure).  it can see that the times are consecutive,
and keep the line going.  and it can really see when there was no
data collected, and leave gaps there.

i feel this is a better separation of concerns, and is more consistent
with the 'data report model' vs the chart rendering.

Verified fixed in build 2.1.0.1007.

An entry was added to the 2.1.0 changelog:

Graphs were incorrect for data that did not change. The graphs appeared as if no data had been gathered.

The Hit Ratios graph had gaps in it where there had not been any activity on the parameters being monitored. For instance, if MyISAM tables were not used, then no Key Cache hit ratio series was plotted, even though the variables were still being collected.