[ovirt-devel] [Devel] [Engine-devel] vds_dynamic refactor
Gilad Chaplik
gchaplik at redhat.com
Thu Apr 10 08:07:12 UTC 2014
----- Original Message -----
> From: "Liran Zelkha" <liran.zelkha at gmail.com>
> To: "Yaniv Dary" <ydary at redhat.com>
> Cc: "Gilad Chaplik" <gchaplik at redhat.com>, "Kobi Ianko" <kobi at redhat.com>, devel at linode01.ovirt.org, "engine-devel"
> <engine-devel at ovirt.org>
> Sent: Wednesday, April 9, 2014 4:22:39 PM
> Subject: Re: [Devel] [Engine-devel] vds_dynamic refactor
>
> On Wed, Apr 9, 2014 at 3:34 PM, Yaniv Dary <ydary at redhat.com> wrote:
> >
> > Why not move only status with changes a lot to statistics and leave
> > everything as is?
> >
> >
> Exactly. No need for a new table. Use the existing ones.
Why should the dwh read entire dynamic record for each status change/available resources change? (for VMs as well).
>
> >
> >
> > Yaniv
> >
> > ________________________________
> >
> > From: "Liran Zelkha" <liran.zelkha at gmail.com>
> > To: "Gilad Chaplik" <gchaplik at redhat.com>
> > Cc: "Kobi Ianko" <kobi at redhat.com>, devel at linode01.ovirt.org,
> > "engine-devel" <engine-devel at ovirt.org>
> > Sent: Monday, April 7, 2014 8:51:00 AM
> >
> > Subject: Re: [Devel] [Engine-devel] vds_dynamic refactor
> >
> >
> >
> >
> > On Sun, Apr 6, 2014 at 11:03 PM, Gilad Chaplik <gchaplik at redhat.com> wrote:
> >>
> >> ----- Original Message -----
> >> > From: "Liran Zelkha" <liran.zelkha at gmail.com>
> >> > To: "Gilad Chaplik" <gchaplik at redhat.com>
> >> > Cc: "Kobi Ianko" <kobi at redhat.com>, devel at linode01.ovirt.org,
> >> > "engine-devel" <engine-devel at ovirt.org>
> >> > Sent: Sunday, April 6, 2014 8:51:02 PM
> >> > Subject: Re: [Devel] [Engine-devel] vds_dynamic refactor
> >> >
> >> > On Sun, Apr 6, 2014 at 6:32 PM, Gilad Chaplik <gchaplik at redhat.com>
> >> > wrote:
> >> >
> >> > > ----- Original Message -----
> >> > > > From: "Liran Zelkha" <liran.zelkha at gmail.com>
> >> > > > To: "Kobi Ianko" <kobi at redhat.com>
> >> > > > Cc: "Gilad Chaplik" <gchaplik at redhat.com>, devel at linode01.ovirt.org,
> >> > > "engine-devel" <engine-devel at ovirt.org>
> >> > > > Sent: Sunday, April 6, 2014 3:40:13 PM
> >> > > > Subject: Re: [Devel] [Engine-devel] vds_dynamic refactor
> >> > > >
> >> > > > On Sun, Apr 6, 2014 at 3:37 PM, Kobi Ianko <kobi at redhat.com> wrote:
> >> > > >
> >> > > > > Joining in...
> >> > > > > From my point of view, in real life a user should have that many
> >> > > > > VDSs
> >> > > on
> >> > > > > one Engine (from a DB point of view).
> >> > > > > Modern DB system handles tables with millions of records and many
> >> > > > > relations, Do we really have a performance issue here?
> >> > > > > We could prefer a more easy to maintain implantation in this case
> >> > > > > over
> >> > > DB
> >> > > > > performance
> >> > > > >
> >> > > > > Yes we do. We make many queries on the VDS view, which is a VERY
> >> > > complex
> >> > > > view.
> >> > > >
> >> > >
> >> > > Actually I quite agree with Kobi, what is the plan for VMs? why do we
> >> > > start with VDS...
> >> > > what is the biggest deploy do you know of?
> >> > >
> >> > We start with VDS because in an idle system, with 200 hosts and several
> >> > thousands VMs, this is what you get as the top queries against the
> >> > database. Look at how many times getvds is called.
> >> > [image: Inline image 1]
> >> > BTW - the second query is an example of abusing the dynamic query
> >> > mechanism. The 4th query (an update command) is a set of useless
> >> > update_vds_dynamic commands.
> >> >
> >> > For reference, the explain plan of get VDS is something like this:
> >> >
> >> > QUERY PLAN
> >> >
> >> > -----------------------------------------------------------------------------------------------------------------------------------------------------------
> >> > Nested Loop (cost=9.30..46.75 rows=6 width=9060) (actual
> >> > time=0.063..0.068 rows=1 loops=1)
> >> > Join Filter: (vds_static.vds_id = vds_statistics.vds_id)
> >> > -> Seq Scan on vds_statistics (cost=0.00..1.01 rows=1 width=109)
> >> > (actual time=0.008..0.008 rows=1 loops=1)
> >> > -> Nested Loop (cost=9.30..45.64 rows=6 width=8983) (actual
> >> > time=0.048..0.052 rows=1 loops=1)
> >> > Join Filter: (vds_groups.vds_group_id =
> >> > vds_static.vds_group_id)
> >> > -> Nested Loop Left Join (cost=0.00..9.29 rows=1 width=1389)
> >> > (actual time=0.013..0.013 rows=1 loops=1)
> >> > -> Seq Scan on vds_groups (cost=0.00..1.01 rows=1
> >> > width=1271) (actual time=0.003..0.003 rows=1 loops=1)
> >> > -> Index Scan using pk_storage_pool on storage_pool
> >> > (cost=0.00..8.27 rows=1 width=134) (actual time=0.008..0.008 rows=1
> >> > loops=1)
> >> > Index Cond: (vds_groups.storage_pool_id = id)
> >> > -> Hash Right Join (cost=9.30..36.28 rows=6 width=7610)
> >> > (actual
> >> > time=0.033..0.037 rows=1 loops=1)
> >> > Hash Cond: (vds_spm_id_map.vds_id = vds_static.vds_id)
> >> > -> Seq Scan on vds_spm_id_map (cost=0.00..22.30
> >> > rows=1230
> >> > width=20) (actual time=0.003..0.003 rows=1 loops=1)
> >> > -> Hash (cost=9.29..9.29 rows=1 width=7606) (actual
> >> > time=0.019..0.019 rows=1 loops=1)
> >> > Buckets: 1024 Batches: 1 Memory Usage: 2kB
> >> > -> Nested Loop (cost=0.00..9.29 rows=1
> >> > width=7606)
> >> > (actual time=0.012..0.013 rows=1 loops=1)
> >> > -> Seq Scan on vds_dynamic (cost=0.00..1.01
> >> > rows=1 width=1895) (actual time=0.006..0.006 rows=1 loops=1)
> >> > -> Index Scan using pk_vds_static on
> >> > vds_static
> >> > (cost=0.00..8.27 rows=1 width=5711) (actual time=0.005..0.006 rows=1
> >> > loops=1)
> >> > Index Cond: (vds_id =
> >> > vds_dynamic.vds_id)
> >> > Total runtime: 0.299 ms
> >> > (19 rows)
> >> >
> >> > It's terrible. Adding any additional join will make this worse. Please
> >> > don't add any more tables...
> >>
> >> Thank you for the detailed explanation, my comments:
> >>
> >> * a very long time isn't an argument for not adding another table (should
> >> be neglectable);
> >> currently we have an unrelated problem, we need to solve it.
> >
> > Of course it is. A very long time for a query that you execute many times
> > is THE factor. Who said the join has no performance effect? Have you
> > tested it? Under load? Under many writes/updates?
> >>
> >>
> >> * > We start with VDS because in an idle system, with 200 hosts and
> >> several
> >> > thousands VMs, this is what you get as the top queries against the
> >> > database.
> >>
> >> so, if fetching VMs takes 10 minutes? and its get called a single time?
> >
> > Where do you see 10 minutes? If you are looking at the red bar it's the
> > inherent time - total query time * number of queries.
> >>
> >>
> >> * you didn't reply on my of my suggestion of constructing the VDS records
> >> in the DB without using joins.
> >
> > If you mean materialized views - we don't have it in Postgres just yet...
> > And even if we do, since we do many updates to vds_statistics and
> > vds_dynamic - I'm not sure it will have positive impact on our
> > performance. If you mean joins in the database - everything that is based
> > on VDS is done in the database. Part of the problem, since we can cache
> > some information and only query the dynamic/statistics part of VDS, but
> > that's another matter.
> >>
> >>
> >>
> >> >
> >> > >
> >> > > > >
> >> > > > > ----- Original Message -----
> >> > > > > > From: "Gilad Chaplik" <gchaplik at redhat.com>
> >> > > > > > To: "Liran Zelkha" <liran.zelkha at gmail.com>
> >> > > > > > Cc: devel at linode01.ovirt.org, "engine-devel"
> >> > > > > > <engine-devel at ovirt.org
> >> > > >
> >> > > > > > Sent: Sunday, April 6, 2014 3:32:26 PM
> >> > > > > > Subject: Re: [Devel] [Engine-devel] vds_dynamic refactor
> >> > > > > >
> >> > > > > > ----- Original Message -----
> >> > > > > > > From: "Liran Zelkha" <liran.zelkha at gmail.com>
> >> > > > > > > To: "Gilad Chaplik" <gchaplik at redhat.com>
> >> > > > > > > Cc: "Itamar Heim" <iheim at redhat.com>,
> >> > > > > > > devel at linode01.ovirt.org,
> >> > > > > > > "engine-devel" <engine-devel at ovirt.org>
> >> > > > > > > Sent: Sunday, April 6, 2014 3:26:24 PM
> >> > > > > > > Subject: Re: [Engine-devel] vds_dynamic refactor
> >> > > > > > >
> >> > > > > > > On Sun, Apr 6, 2014 at 3:18 PM, Gilad Chaplik
> >> > > > > > > <gchaplik at redhat.com
> >> > > >
> >> > > > > wrote:
> >> > > > > > >
> >> > > > > > > > ----- Original Message -----
> >> > > > > > > > > From: "Itamar Heim" <iheim at redhat.com>
> >> > > > > > > > > To: "Liran Zelkha" <liran.zelkha at gmail.com>
> >> > > > > > > > > Cc: "Gilad Chaplik" <gchaplik at redhat.com>,
> >> > > > > devel at linode01.ovirt.org,
> >> > > > > > > > "engine-devel" <engine-devel at ovirt.org>
> >> > > > > > > > > Sent: Sunday, April 6, 2014 11:33:12 AM
> >> > > > > > > > > Subject: Re: [Engine-devel] vds_dynamic refactor
> >> > > > > > > > >
> >> > > > > > > > > On 04/06/2014 11:32 AM, Liran Zelkha wrote:
> >> > > > > > > > > >
> >> > > > > > > > > >
> >> > > > > > > > > >
> >> > > > > > > > > > On Sun, Apr 6, 2014 at 11:22 AM, Itamar Heim <
> >> > > iheim at redhat.com
> >> > > > > > > > > > <mailto:iheim at redhat.com>> wrote:
> >> > > > > > > > > >
> >> > > > > > > > > > On 04/03/2014 07:51 PM, Liran Zelkha wrote:
> >> > > > > > > > > >
> >> > > > > > > > > > The problem is with both updates and selects.
> >> > > > > > > > > > For selects - to get all the information for the
> >> > > > > > > > > > VDS
> >> > > we
> >> > > > > have
> >> > > > > > > > > > multiple
> >> > > > > > > > > > joins. Adding another one will hurt performance
> >> > > > > > > > > > even
> >> > > > > more.
> >> > > > > > > > > > For updates - we have vds_static thats hardly
> >> > > changed.
> >> > > > > > > > > > vds_statistics
> >> > > > > > > > > > that changes all the time. vds_dynamic is not
> >> > > > > > > > > > changed
> >> > > > > allot -
> >> > > > > > > > but
> >> > > > > > > > > > is
> >> > > > > > > > > > updated all the time because of the status. I
> >> > > > > > > > > > think
> >> > > it's
> >> > > > > best
> >> > > > > > > > to
> >> > > > > > > > > > split
> >> > > > > > > > > > it to the two existing tables (BTW - relevant
> >> > > > > > > > > > for VM
> >> > > as
> >> > > > > well)
> >> > > > > > > > > >
> >> > > > > > > > > >
> >> > > > > > > > > > but we don't update it unless the status has
> >> > > > > > > > > > changed,
> >> > > which
> >> > > > > is a
> >> > > > > > > > > > rare occurance?
> >> > > > > > > > > >
> >> > > > > > > > > > Actually - no. We can definitely see times we are
> >> > > > > > > > > > updating
> >> > > > > > > > > > vds_dynamic
> >> > > > > > > > > > with no reason at all. I tried to create patches for
> >> > > > > > > > > > that -
> >> > > but
> >> > > > > it
> >> > > > > > > > > > happens from many different places in the code.
> >> > > > > > > > >
> >> > > > > > > > > what would be updated vds_dyanmic for status not
> >> > > > > > > > > originating in
> >> > > > > update
> >> > > > > > > > > run time info?
> >> > > > > > > >
> >> > > > > > > > We have separate DB flows for that (updateStatus and
> >> > > > > > > > updatePartialVdsDynamicCalc and more in
> >> > > VdsDynamicDAODbFacadeImpl).
> >> > > > > > > > A question: do you know if we update status in
> >> > > > > > > > updateVdsDynamic?
> >> > > :-)
> >> > > > > not
> >> > > > > > > > sure but I found a possible race for pending resources (cpu,
> >> > > mem),
> >> > > > > LOL
> >> > > > > > > > :-)
> >> > > > > > > >
> >> > > > > > > > I think we do but not sure. Will check.
> >> > > > > >
> >> > > > > > Of course it is, that was a rhetorical question :-) (a lot of
> >> > > emoticons
> >> > > > > and
> >> > > > > > LOLs ;-))
> >> > > > > >
> >> > > > > > >
> >> > > > > > >
> >> > > > > > > > Still holds my original thought for having vds_on_boot.
> >> > > > > > > >
> >> > > > > > > >
> >> > > > > > > >
> >> > > > > > > Let's talk f2f on Tuesday?
> >> > > > > >
> >> > > > > > I'd prefer to reach conclusions here, I'd like everyone to be
> >> > > involved
> >> > > > > in a
> >> > > > > > root issue like this one.
> >> > > > >
> >> > > >
> >> > > > What is the update frequency of this field?
> >> > > >
> >> > >
> >> > > which field?
> >> > > status? pending resources? on boot fields?
> >> > > iinm, status is updated mostly by user actions, at least in positive
> >> > > scenarios, and not that often.
> >> > >
> >> > >
> >> > > > > >
> >> > > > > > >
> >> > > > > > _______________________________________________
> >> > > > > > Devel mailing list
> >> > > > > > Devel at ovirt.org
> >> > > > > > http://lists.ovirt.org/mailman/listinfo/devel
> >> > > > > >
> >> > > > >
> >> > > >
> >> > >
> >> >
> >
> >
> >
> > _______________________________________________
> > Devel mailing list
> > Devel at ovirt.org
> > http://lists.ovirt.org/mailman/listinfo/devel
> >
> >
>
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