Re: [ovirt-devel] [Devel] [Engine-devel] vds_dynamic refactor

From: "Liran Zelkha" <liran.zelkha(a)gmail.com&gt; To: "Yaniv Dary" <ydary(a)redhat.com&gt; Cc: "Gilad Chaplik" <gchaplik(a)redhat.com&gt;, "Kobi Ianko" <kobi(a)redhat.com&gt;, devel(a)linode01.ovirt.org, "engine-devel" <engine-devel(a)ovirt.org&gt; 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(a)redhat.com&gt; 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.

> > > Yaniv > > ________________________________ > > From: "Liran Zelkha" <liran.zelkha(a)gmail.com&gt; > To: "Gilad Chaplik" <gchaplik(a)redhat.com&gt; > Cc: "Kobi Ianko" <kobi(a)redhat.com&gt;, devel(a)linode01.ovirt.org, > "engine-devel" <engine-devel(a)ovirt.org&gt; > 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(a)redhat.com&gt; wrote: >> >> ----- Original Message ----- >> > From: "Liran Zelkha" <liran.zelkha(a)gmail.com&gt; >> > To: "Gilad Chaplik" <gchaplik(a)redhat.com&gt; >> > Cc: "Kobi Ianko" <kobi(a)redhat.com&gt;, devel(a)linode01.ovirt.org, >> > "engine-devel" <engine-devel(a)ovirt.org&gt; >> > 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(a)redhat.com&gt; >> > wrote: >> > >> > > ----- Original Message ----- >> > > > From: "Liran Zelkha" <liran.zelkha(a)gmail.com&gt; >> > > > To: "Kobi Ianko" <kobi(a)redhat.com&gt; >> > > > Cc: "Gilad Chaplik" <gchaplik(a)redhat.com&gt;, devel(a)linode01.ovirt.org, >> > > "engine-devel" <engine-devel(a)ovirt.org&gt; >> > > > 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(a)redhat.com&gt; 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(a)redhat.com&gt; >> > > > > > To: "Liran Zelkha" <liran.zelkha(a)gmail.com&gt; >> > > > > > Cc: devel(a)linode01.ovirt.org, "engine-devel" >> > > > > > <engine-devel(a)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(a)gmail.com&gt; >> > > > > > > To: "Gilad Chaplik" <gchaplik(a)redhat.com&gt; >> > > > > > > Cc: "Itamar Heim" <iheim(a)redhat.com&gt;, >> > > > > > > devel(a)linode01.ovirt.org, >> > > > > > > "engine-devel" <engine-devel(a)ovirt.org&gt; >> > > > > > > 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(a)redhat.com >> > > > >> > > > > wrote: >> > > > > > > >> > > > > > > > ----- Original Message ----- >> > > > > > > > > From: "Itamar Heim" <iheim(a)redhat.com&gt; >> > > > > > > > > To: "Liran Zelkha" <liran.zelkha(a)gmail.com&gt; >> > > > > > > > > Cc: "Gilad Chaplik" <gchaplik(a)redhat.com&gt;, >> > > > > devel(a)linode01.ovirt.org, >> > > > > > > > "engine-devel" <engine-devel(a)ovirt.org&gt; >> > > > > > > > > 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(a)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(a)ovirt.org >> > > > > > http://lists.ovirt.org/mailman/listinfo/devel >> > > > > > >> > > > > >> > > > >> > > >> > > > > > _______________________________________________ > Devel mailing list > Devel(a)ovirt.org > http://lists.ovirt.org/mailman/listinfo/devel > >