----- Original Message -----
From: "Yaniv Dary" <ydary@redhat.com> To: "Gilad Chaplik" <gchaplik@redhat.com> Cc: "Liran Zelkha" <liran.zelkha@gmail.com>, "Kobi Ianko" <kobi@redhat.com>, devel@linode01.ovirt.org, "engine-devel" <engine-devel@ovirt.org> Sent: Thursday, April 10, 2014 11:44:32 AM Subject: Re: [Devel] [Engine-devel] vds_dynamic refactor
----- Original Message -----
From: "Gilad Chaplik" <gchaplik@redhat.com> To: "Liran Zelkha" <liran.zelkha@gmail.com> Cc: "Yaniv Dary" <ydary@redhat.com>, "Kobi Ianko" <kobi@redhat.com>, devel@linode01.ovirt.org, "engine-devel" <engine-devel@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@gmail.com> To: "Yaniv Dary" <ydary@redhat.com> Cc: "Gilad Chaplik" <gchaplik@redhat.com>, "Kobi Ianko" <kobi@redhat.com>, devel@linode01.ovirt.org, "engine-devel" <engine-devel@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@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.
dynamic\statistics - dynamic\static to fully understand it, we have 2 triggers to collect from dynamic?
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.
oh... I thought that we had a trigger to dynamic (if ^ is correct we have). +1 (out of 1) for you comment :-) and thanks Yaniv the elaborate explanation!
Yaniv
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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: 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@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" > > > > <engine-devel@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@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 > > > > > > > > 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@ovirt.org > > > > http://lists.ovirt.org/mailman/listinfo/devel > > > > > > > > > >
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