[kdepim-users] Tbird versus Kmail, performance

[James Cain]

It might be beneficial also to take this conversation to IRC, since that's
where you'll find the most ears for this seemingly important discussion :)

On Sat, Nov 15, 2014 at 5:17 PM, Pablo Sanchez <pablo at blueoakdb.com> wrote:

> [ Comments below, in-line ]
>
> On 11/15/2014 05:05 PM, René J.V. Bertin wrote:
> > On Saturday November 15 2014 16:38:29 Pablo Sanchez wrote:
> >
> > Hi,
>
> Hi Rene,
>
> >> When I engage in performance tuning efforts, unless a previous
> >> version's changes are minimal, I only look at the present.  It's a
> >> bit easier when a problem is glaring.
> >
> > I'm not exactly sure what you're saying here.
>
> Oh, sorry for being unclear.  What I was trying to say is given the
> set of changes from one version to others, it's usually most fruitful
> to look at the current s/w and fix it.
>
> > I know one has to be very careful with subjective impressions like
> > "everything was better before", but in this case I was pretty sure
> > that the real issues started after updating to 4.14
>
> I'm not denying the above.  I suspect your impressions are right.
> Ultimately the goal is to fix the existing s/w so that's why I tend to
> focus on it (when I'm in charge of fixing P&T issues.  :)
>
> > after Daniel's explanations from yesterday which suggest that the
> > database is not the bottleneck.
>
> The data doesn't indicate the above at all.  What I saw is we're
> hitting the database very hard.  Doing some crude sampling against the
> database I showed the queries.  These queries, as I mentioned, are
> nearly unbounded:  no timestamp is used to reduce their database
> bandwidth demand.
>
> I also indicated how it's possible to add a timestamp and set it when
> the row is added to the table.  This timestamp is used to reduce the
> demand against the database to improve scalability.
>
> Let me give you an example.  If you run a query against a table and
> crunch through 100,000 rows (let's just ignore how much space they
> require) and if all the data is in cache, from the O/S perspective,
> the DBMS will appear as it's only consuming CPU.
>
> If you repeatedly run the query many times, the DBMS will be CPU bound
> as it services the query, over and over again.
>
> From what I saw, we have /several/ of these queries running over and
> over again.
>
> Now, if you take the same query but add a timestamp filter to only
> return the rows between the last time it ran and /now/, it may be that
> we only loaded, say, 100 mail messages between queries.  Crunching 100
> rows rather than 100,000 rows ... well .. it's obvious right?  Less
> demand and thus we improve scalability.
>
> I hope the above helps explain it.
>
> Daniel didn't respond to me personally so I assume either a) he's away
> or b) not interested in my help.  :)
>
> > Anyway, I kept akonadi at the latest version (a recent git
> > clone). Talking about database options:  I came across a suggestion
> > on one of the Arch wikipages to unset an innodb setting related to
> > aio_write on ZFS. Not that I ever saw the error in question, but I
> > guess I should figure out what that setting does (I just suspended
> > my Linux rig so I don't have the exact name handy right now).
>
> The database is not I/O bound.  It's CPU bound so unfortunately no
> amount of I/O tuning is going to help.
>
> Cheers,
> --
> Pablo Sanchez - Blueoak Database Engineering, Inc
> Ph:    819.459.1926         Blog:  http://pablo-blog.blueoakdb.com
> iNum:  883.5100.0990.1054
>
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