[ovs-dev] [PATCH 2/3] Save performance stats to database.

[Ben Pfaff]

On Mon, Dec 18, 2017 at 04:51:38PM -0600, Mark Michelson wrote:
> This commit builds on the performance library by storing compiled
> statistics in the OVS vswitchd database.
> 
> This can make it more useful for administrators to keep tabs on
> performance in real time and make adjustments if necessary.
> 
> Signed-off-by: Mark Michelson <mmichels at redhat.com>

It seems somewhat odd to put this table in the OVS database, when the
(initial) intent is for the performance measurements to come from OVN
instead.

performance_destroy() needs to be called within a database transaction.

Database transactions don't always succeed; sometimes they fail and need
to be retried.  I think that this will happen naturally with
performance_run(), but I think that the deletion from
performance_destroy() will not be retried if it fails (because the
internal object has been destroyed).  This is not ideal.

One way to fix that might be to make performance_run() something that
runs once, in the daemon's main loop, instead of once per performance
object.  Then, performance_run() could compare the database table to
'performances', adding missing rows, updating existing rows, and
deleting rows that should be abandoned.

The database schema seems pretty rough to me.  It is going to be hard to
modify and extend.  I can think of a few ways to make it more flexible.
One would be to have columns (name, age, samples, average, min, max,
percentiles), where percentiles would be a map from a real (a
percentile) to its score, and each performance object would have three
rows, with ages 1, 5, and 10, (You might consider using columns of type
'real'.)  Another would be to have (name, samples, average, min, max,
p95), where average, min, max, and p95 were maps from an age to the
value for that age.  There are other possibilities too.

Thanks,

Ben.