On Thu, Feb 6, 2020 at 1:57 AM Mahendra Singh Thalor <mahi6...@gmail.com> wrote: > > On Wed, 5 Feb 2020 at 12:07, Masahiko Sawada <sawada.m...@gmail.com> wrote: > > > > On Mon, Feb 3, 2020 at 8:03 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > > > > > On Tue, Jun 26, 2018 at 12:47 PM Masahiko Sawada <sawada.m...@gmail.com> > > > wrote: > > > > > > > > On Fri, Apr 27, 2018 at 4:25 AM, Robert Haas <robertmh...@gmail.com> > > > > wrote: > > > > > On Thu, Apr 26, 2018 at 3:10 PM, Andres Freund <and...@anarazel.de> > > > > > wrote: > > > > >>> I think the real question is whether the scenario is common enough > > > > >>> to > > > > >>> worry about. In practice, you'd have to be extremely unlucky to be > > > > >>> doing many bulk loads at the same time that all happened to hash to > > > > >>> the same bucket. > > > > >> > > > > >> With a bunch of parallel bulkloads into partitioned tables that > > > > >> really > > > > >> doesn't seem that unlikely? > > > > > > > > > > It increases the likelihood of collisions, but probably decreases the > > > > > number of cases where the contention gets really bad. > > > > > > > > > > For example, suppose each table has 100 partitions and you are > > > > > bulk-loading 10 of them at a time. It's virtually certain that you > > > > > will have some collisions, but the amount of contention within each > > > > > bucket will remain fairly low because each backend spends only 1% of > > > > > its time in the bucket corresponding to any given partition. > > > > > > > > > > > > > I share another result of performance evaluation between current HEAD > > > > and current HEAD with v13 patch(N_RELEXTLOCK_ENTS = 1024). > > > > > > > > Type of table: normal table, unlogged table > > > > Number of child tables : 16, 64 (all tables are located on the same > > > > tablespace) > > > > Number of clients : 32 > > > > Number of trials : 100 > > > > Duration: 180 seconds for each trials > > > > > > > > The hardware spec of server is Intel Xeon 2.4GHz (HT 160cores), 256GB > > > > RAM, NVMe SSD 1.5TB. > > > > Each clients load 10kB random data across all partitioned tables. > > > > > > > > Here is the result. > > > > > > > > childs | type | target | avg_tps | diff with HEAD > > > > --------+----------+---------+------------+------------------ > > > > 16 | normal | HEAD | 1643.833 | > > > > 16 | normal | Patched | 1619.5404 | 0.985222 > > > > 16 | unlogged | HEAD | 9069.3543 | > > > > 16 | unlogged | Patched | 9368.0263 | 1.032932 > > > > 64 | normal | HEAD | 1598.698 | > > > > 64 | normal | Patched | 1587.5906 | 0.993052 > > > > 64 | unlogged | HEAD | 9629.7315 | > > > > 64 | unlogged | Patched | 10208.2196 | 1.060073 > > > > (8 rows) > > > > > > > > For normal tables, loading tps decreased 1% ~ 2% with this patch > > > > whereas it increased 3% ~ 6% for unlogged tables. There were > > > > collisions at 0 ~ 5 relation extension lock slots between 2 relations > > > > in the 64 child tables case but it didn't seem to affect the tps. > > > > > > > > > > AFAIU, this resembles the workload that Andres was worried about. I > > > think we should once run this test in a different environment, but > > > considering this to be correct and repeatable, where do we go with > > > this patch especially when we know it improves many workloads [1] as > > > well. We know that on a pathological case constructed by Mithun [2], > > > this causes regression as well. I am not sure if the test done by > > > Mithun really mimics any real-world workload as he has tested by > > > making N_RELEXTLOCK_ENTS = 1 to hit the worst case. > > > > > > Sawada-San, if you have a script or data for the test done by you, > > > then please share it so that others can also try to reproduce it. > > > > Unfortunately the environment I used for performance verification is > > no longer available. > > > > I agree to run this test in a different environment. I've attached the > > rebased version patch. I'm measuring the performance with/without > > patch, so will share the results. > > > > Thanks Sawada-san for patch. > > From last few days, I was reading this thread and was reviewing v13 patch. > To debug and test, I did re-base of v13 patch. I compared my re-based patch > and v14 patch. I think, ordering of header files is not alphabetically in > v14 patch. (I haven't reviewed v14 patch fully because before review, I > wanted to test false sharing). While debugging, I didn't noticed any hang or > lock related issue. > > I did some testing to test false sharing(bulk insert, COPY data, bulk insert > into partitions tables). Below is the testing summary. > > Test setup(Bulk insert into partition tables): > autovacuum=off > shared_buffers=512MB -c max_wal_size=20GB -c checkpoint_timeout=12min > > Basically, I created a table with 13 partitions. Using pgbench, I inserted > bulk data. I used below pgbench command: > ./pgbench -c $threads -j $threads -T 180 -f insert1.sql@1 -f insert2.sql@1 -f > insert3.sql@1 -f insert4.sql@1 postgres > > I took scripts from previews mails and modified. For reference, I am > attaching test scripts. I tested with default 1024 slots(N_RELEXTLOCK_ENTS = > 1024). > > Clients HEAD (tps) With v14 patch (tps) > %change (time: 180s) > 1 92.979796 100.877446 > +8.49 % > 32 392.881863 388.470622 > -1.12 % > 56 551.753235 528.018852 > -4.30 % > 60 648.273767 653.251507 > +0.76 % > 64 645.975124 671.322140 > +3.92 % > 66 662.728010 673.399762 > +1.61 % > 70 647.103183 660.694914 > +2.10 % > 74 648.824027 676.487622 > +4.26 % > > From above results, we can see that in most cases, TPS is slightly increased > with v14 patch. I am still testing and will post my results. >
The number at 56 and 74 client count seem slightly suspicious. Can you please repeat those tests? Basically, I am not able to come up with a theory why at 56 clients the performance with the patch is a bit lower and then at 74 it is higher. > I want to test extension lock by blocking use of fsm(use_fsm=false in code). > I think, if we block use of fsm, then load will increase into extension lock. > Is this correct way to test? > Hmm, I think instead of directly hacking the code, you might want to use the operation (probably cluster or vacuum full) where we set HEAP_INSERT_SKIP_FSM. I think along with this you can try with unlogged tables because that might stress the extension lock. In the above test, you might want to test with a higher number of partitions (say up to 100) as well. Also, see if you want to use the Copy command. > Please let me know if you have any specific testing scenario. > Can you test the scenario mentioned by Konstantin Knizhnik [1] where this patch has shown significant gain? You might want to use a higher core count machine to test it. One thing we can do is to somehow measure the collisions on each bucket. [1] - https://www.postgresql.org/message-id/ef81da49-d491-db86-3ef6-5138d091fe91%40postgrespro.ru -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
