[ovirt-devel] [Devel] [Engine-devel] vds_dynamic refactor
Yaniv Dary
ydary at redhat.com
Thu Apr 10 08:44:32 UTC 2014
----- Original Message -----
> From: "Gilad Chaplik" <gchaplik at redhat.com>
> To: "Liran Zelkha" <liran.zelkha at gmail.com>
> Cc: "Yaniv Dary" <ydary at redhat.com>, "Kobi Ianko" <kobi at redhat.com>, devel at linode01.ovirt.org, "engine-devel"
> <engine-devel at ovirt.org>
> Sent: Thursday, April 10, 2014 11:07:12 AM
> Subject: Re: [Devel] [Engine-devel] vds_dynamic refactor
>
> ----- 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).
The DWH doesn't work like that. We create views over dynamic\statistics and dynamic\static they go the the configuration and stats tables on the history db side.
>From dynamic\statistics we collect every minute no matter what and from dynamic\static we collect only when update_date changes in static.
We can not rely on the dynamic update_date since it changes so much, so from my point of view if we can cause minimal changes in dynamic and move status to statistics it would the best thing.
What we have currently is a task that run once a hour and checks if any change was made in the dynamic table (via very ugly joins and rejects) and sync is there was any change.
It would even be better if you also move swap_size which doesn't change much to dynamic.
>
> >
> > >
> > >
> > > 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
> > >
> > >
> >
>
More information about the Devel
mailing list