[Devel] [Engine-devel] vds_dynamic refactor
Gilad Chaplik
gchaplik at redhat.com
Sun Apr 6 20:03:47 UTC 2014
----- 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.
* > 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?
* you didn't reply on my of my suggestion of constructing the VDS records in the DB without using joins.
>
> >
> > > >
> > > > ----- 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
> > > > >
> > > >
> > >
> >
>
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