On Sun, Apr 6, 2014 at 11:03 PM, Gilad Chaplik <gchaplik@redhat.com> wrote:
----- Original Message -----
From: "Liran Zelkha" <liran.zelkha@gmail.com> To: "Gilad Chaplik" <gchaplik@redhat.com> Cc: "Kobi Ianko" <kobi@redhat.com>, devel@linode01.ovirt.org, "engine-devel" <engine-devel@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@redhat.com> wrote:
----- Original Message -----
From: "Liran Zelkha" <liran.zelkha@gmail.com> To: "Kobi Ianko" <kobi@redhat.com> Cc: "Gilad Chaplik" <gchaplik@redhat.com>, devel@linode01.ovirt.org, "engine-devel" <engine-devel@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@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@redhat.com> To: "Liran Zelkha" <liran.zelkha@gmail.com> Cc: devel@linode01.ovirt.org, "engine-devel" <
Sent: Sunday, April 6, 2014 3:32:26 PM Subject: Re: [Devel] [Engine-devel] vds_dynamic refactor
----- Original Message ----- > From: "Liran Zelkha" <liran.zelkha@gmail.com> > To: "Gilad Chaplik" <gchaplik@redhat.com> > Cc: "Itamar Heim" <iheim@redhat.com>, devel@linode01.ovirt.org
,
> "engine-devel" <engine-devel@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@redhat.com
wrote:
> > > ----- Original Message ----- > > > From: "Itamar Heim" <iheim@redhat.com> > > > To: "Liran Zelkha" <liran.zelkha@gmail.com> > > > Cc: "Gilad Chaplik" <gchaplik@redhat.com>, devel@linode01.ovirt.org, > > "engine-devel" <engine-devel@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@redhat.com > > > > <mailto:iheim@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
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
engine-devel@ovirt.org think 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.
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