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

Why not move only status with changes a lot to statistics and leave everything as is?

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