April 2014 - developers - lists.mariadb.org

[Maria-developers] New MariaDB builds: regular trusty and special kvm-deb-sid-pbuilder-amd and (Re: MariaDB)
by Otto Kekäläinen 01 Sep '14

01 Sep '14

Hello! 2014-02-04 20:41 GMT+02:00 Daniel Bartholomew <dbart(a)mariadb.com>: > On Tue, Feb 4, 2014 at 5:39 AM, Kristian Nielsen > <knielsen(a)knielsen-hq.org> wrote: >>> And while you are at it, please also consider setting up an instance >>> 'kvm-deb-sid-pbuilder-amd64' that provides a Debian unstable >> >> Daniel, can you prepare new sets of VMs for Ubuntu trusty and Debian sid? >> Then I can try to setup Buildbot to do these builds. > > Ok, will do. I should have them up and running before the end of the week. Any updates on this?

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[Maria-developers] [GSoC] Introduction Mail
by Anshu Avinash 04 Aug '14

04 Aug '14

Hi all, I have been accepted for the project "Self-Tuning Optimizer". I will be doing this project under the mentorship of Sergei Golubchik. There is already a task created which will track the progress for this project: https://mariadb.atlassian.net/browse/MDEV-350 . I'll start with getting familiar with the code base, reading some literature on cost estimation in optimizer and interacting with community. About me: I am currently a 4th year student pursuing B.Tech - M.Tech dual degree in Computer Science and Engineering from Indian Institute of Technology (IIT) – Kanpur, India. This would be my first GSoC project. I had done an internship at Facebook last year. I'll also be maintaining a blog at http://igniting.in . I'm really excited to be a part of mariadb and I hope to make a significant contribution to it. Regards Anshu Avinash

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[Maria-developers] TIME/DATETIME/TIMESTAMP data types with fractional precision
by Alexander Barkov 26 Jun '14

26 Jun '14

Hello, I propose to switch to MySQL-5.6 TIME/DATETIME/TIMESTAMP formats by default and deprecate MariaDB native temporal data types, together with pre-5.6 non-fractional types. The problem is that MariaDB native data types (and MySQL-5.5 non-fractional data types) do not work with row based replication in case of: TIME(N) -> TIME(M) There is no metadata telling about the column precision in the binary log file. It can only work when N=M. MySQL-5.6 uses separate type codes for the temporal data types: MYSQL_TYPE_TIME2 MYSQL_TYPE_DATETIME2 MYSQL_TYPE_TIMESTAMP2 and does put precision into metadata in the binary log. So it works for N != M. There is a JIRA task for this: MDEV-5377 Row-based replication of MariaDB temporal data types with FSP>0 into a different column type I'd propose to do it in 10.1.x, as 10.0.x is too late. Greetings.

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[Maria-developers] Extendet FederatedX storage engine to support updating Sphinx RT indexes
by Markus Lidel 12 Jun '14

12 Jun '14

Hello, the Sphinx Search engine has RT indexes, which could be updated with a subset of SQL commands, refered to as SphinxQL: http://sphinxsearch.com/docs/2.1.1/sphinxql-reference.html Because the FederatedX storage engine uses some commands, which Sphinx does not know, here is a patch, wich extends the FederatedX storage engine to support this subset of commands. Now its possible to update Sphinx RT indexes directly from MariaDB. To create a connection to the RT index in the Sphinx default RT-index: index rt { type = rt path = @CONFDIR@/data/rt rt_field = title rt_field = content rt_attr_string = title rt_attr_string = content rt_attr_uint = gid } you just have to call: CREATE TABLE `rt` ( `id` BIGINT UNSIGNED NOT NULL, `title` TEXT, `content` TEXT, `gid` INT UNSIGNED ) ENGINE=FEDERATED CONNECTION='sphinxql://root@localhost:9306/rt'; It would be great, if the attached patch could be integrated into MariaDB. If you have any suggestions, please feel free to contact me. Best regards, Markus Lidel

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Re: [Maria-developers] [GSoC] Accepted student ready to work : )
by Pablo Estrada 10 Jun '14

10 Jun '14

Hello all, I'm still interested on a call, (I would make sure to write down everything as part of an email to keep it clearly organized here), but as Elena suggested, I'll try to look at Sergei's bzr repo first, and all the documentation. In any case, I already have a decent idea of how the data is arranged. I can see how it is difficult to trace test results back to code changes directly, but it might be possible. I still haven't figured out how to recognize what code changes pertain to the same 'history', or 'line' (I think that you were not considering this in your experiments... and it might turn out to not be relevant at all, but I still want to consider it, to try to make a more complete model). So I have just two questions that should be easy to answer by email: 1. In your graphs, exactly, what do you mean by Precision? What about Recall? And cutoff? 2. I looked at your launchpad profile but I can't seem to find the repo with your tests (if you even pushed it to lp at all). Is it available? That's it for today : ) Until next time. Pablo On Thu, Apr 24, 2014 at 12:28 AM, Sergei Golubchik <serg(a)skysql.com> wrote: > On April 23, 2014 10:07:23 AM CEST, Pablo Estrada wrote: > > >If it's not too inconvenient, do you think we could set up a Google > >Hangout > >or a Skype call on Monday to go over a few questions quickly? > > > Definitely. This week I'm on vacations and without a laptop, back home on > Sunday. So, Monday is fine. But please if you have specific questions - ask > them now in emails. I'll prepare answers for Monday, but it'll take time to > remember everything. That is, if you will wait with questions till the > call, I might not be able to remember the answer on the spot. > Regards, > Sergei >

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[Maria-developers] Please review a patch fixing a few MDEV-6001 blockers
by Alexander Barkov 03 Jun '14

03 Jun '14

Hi Sergei, can you please review my patch fixing a few bugs that are blockers for MDEV-6001? - MDEV-4858 Wrong results for a huge unsigned value inserted into a TIME column - MDEV-6097 Inconsistent results for CAST(int,decimal,double AS DATETIME) - MDEV-6099 Bad results for DATE_ADD(.., INTERVAL 2000000000000000000.0 SECOND) - MDEV-6100 No warning on CAST(9000000 AS TIME) - MDEV-6101 Hybrid functions do not add CURRENT_DATE when converting TIME to DATETIME - MDEV-6102 Comparison between TIME and DATETIME does not use CURRENT_DATE Thanks.

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[Maria-developers] connect.alter fails
by Alexander Barkov 07 May '14

07 May '14

Hello Olivier, connect.alter fails when built without XML support complaining about unsupported table type XML. I guess it should be skipped. connect.alter also fails with libxml2 with these symptoms: --- /home/bar/maria-bzr/maria-10.0-connect/storage/connect/mysql-test/connect/r/alter.result 2014-03-23 11:32:34.519624000 +0400 +++ /home/bar/maria-bzr/maria-10.0-connect/storage/connect/mysql-test/connect/r/alter.reject 2014-03-23 11:48:43.251680097 +0400 @@ -1,3 +1,5 @@ +Warnings: +Warning 1105 No file name. Table will use t1.xml Please fix. A remainder: please check every push in BuildBot: http://buildbot.askmonty.org/buildbot/grid?branch=10.0-connect

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[Maria-developers] Analysing degraded performance at high concurrency in sysbench OLTP
by Kristian Nielsen 02 May '14

02 May '14

At the Barcelona meeting in January, I promised to take a look at the high-concurrency sysbench OLTP benchmarks, and now I finally had the time do do this. There was a lot of work on LOCK_open by Svoj and Serg. If I have understood correctly, the basic problem was that at high concurrency (like, 512 threads), the TPS is only a small fraction of the peak throughput at lower concurrency. Basically, the server "falls over" and starts trashing instead of doing real work, due to some kind of inter-processor communication overhead. I started from Axel' OLTP sysbench runs and scripts, using 10.0 from bzr revno:4151 (revid:svoj@mariadb.org-20140415072957-yeir4jvokyilw5hp). I compiled without performance schema and with PGO, and ran sysbench 0.5 OLTP. (I just realised that my runs are with 32 tables, while I think the benchmarks in January focused on single-table runs. Maybe I need to re-do my analysis with the single-table benchmark, or perhaps it is too artificial to matter much?). In the read-only sysbench, the server mostly does not fall over. I guess this is due to the work by Svoj on eliminating LOCK_open? But in read-write, performance drops dramatically at high concurrency. TPS drops to 2600 at 512 threads compared to a peak of around 13000 (numbers here are approximate only, they vary somewhat between different runs). So I analysed the r/w benchmark with the linux `perf` tool. It turns out two-thirds of the time is spent in a single kernel function _raw_spin_lock(): - 66.26% mysqld [kernel.kallsyms] [k] _raw_spin_lock Digging further using --call-graph, this turns out to be mostly futex waits (and futex wakeups) from inside InnoDB locking primitives. Calls like sync_array_get_and_reserve_cell() and sync_array_wait_event() stand out in particular. So this is related to the non-scalable implementation in InnoDB of locking primitives, which is a known problem. I think Mark Callaghan has written about it a couple of times. Last time I looked at the code, every single mutex wait has to take a global mutex protecting some global arrays and stuff. I even remember seeing code that at mutex release would pthread_signal_broadcast() _every_ waiter, all of them waking up, only to all (except one) go do another wait. This is a kiler for scalability. While investigating, I discovered the variable innodb_sync_array_size, which I did not know about. It seems to split the mutex for some of the synchronisation operations. So I tried to re-run the benchmark with innodb_sync_array_size set to 8 and 64. In both cases, I got significant improvement, TPS increase to 5900, twice the value with innodb_sync_array_size set to the default of 1. So it is clear that the main limitation in this benchmark was the non-scalable InnoDB synchronisation implementation. After tuning innodb_sync_array_size, time spent in _raw_spin_lock() is down to half what it was before (33% of total time): + 33.77% mysqld [kernel.kallsyms] [k] _raw_spin_lock Now investigating call-graphs show that the sync_array operations are much less visible. Instead mutex_create_func(), called from dict_mem_table_create(), is the one that turns up prominently in the profile. I am not familiar with what this part of the InnoDB code is doing, but what I saw from a quick look is that it creates a mutex - and there is another global mutex needed for this, which again limits scalability. It is a bit surprising to see mutex creation being the most significant bottleneck in the benchmark. I would have assumed that most mutexes could be created up-front and re-used? It is possible that this is a warm-up thing, maybe the code is filling up the buffer pool or some table-cache like thing inside InnoDB? Because I see TPS being rather low for the first 150 seconds of the run (around 3000), and then increasing suddenly to around 8000-9000 for the rest. This might be worth investigating further. So in summary, my investigations found that the bottleneck in this benchmark, and the likely cause of the fall-over, is a scalability problem with InnoDB locking primitives. The sync_array part seems to be mitigated to some degree by innodb_sync_array_size, the mutex creation part still needs to be investigated. I wonder if the InnoDB team @ Oracle is doing something for this in 5.7? Does anyone know? I vaguely recall reading something about it, but I am not sure. It would seem a waste to duplicate their efforts. In any case, I hope this was useful. As part of this investigation, I installed a new 3.14 kernel on the lizard2 machine and a new `perf` installation, which seems to work well to do more detailed investigations of these kind of issues. So let me know if there are other benchmarks that I should look into. One thing that could be interesting is to look for false sharing; there are some performance counters that Intel manuals describe can be used for this. As an aside: In my tests, once concurrency becomes high enough that the server falls over, the actual TPS number becomes mostly meaningless. Eg. I saw putting dummy pause loops into the code increasing TPS. If TPS stabilises at N% of peak throughput as concurrency goes to infinity, then we can compare N. But if N goes to zero as concurrency goes to infinite, I think it is meaningless to compare actual TPS numbers - we should instead focus on removing the fall-over behaviour. (Maybe this is already obvious to you, I have not followed the previous benchmark efforts that closely). Hope this helps, - Kristian.

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[Maria-developers] Next steps in improving single-threaded performance
by Kristian Nielsen 01 May '14

01 May '14

I have been analysing CPU bottlenecks in single-threaded sysbench read-only load. I found that icache misses is the main bottleneck, and that profile-guided compiler optimisation (PGO) with GCC gives a large speedup, 25% or more. (More details in my blog posts: http://kristiannielsen.livejournal.com/17676.html http://kristiannielsen.livejournal.com/18168.html ) Now I would like to ask for some discussions/help in how to get this implemented in practice. It involves changing the build process for our binaries: First compile with gcc --coverage, then run some profile workload, then recompile with -fprofile-use. I implemented a simple program to generate some profile load: https://github.com/knielsen/gen_profile_load It runs a bunch of simple insert/select/update/delete, with different combinations of storage engine, binlog format, and client API. It is designed to run inside the build tree and handle starting and stopping the server being tested, so it is pretty close to a working setup. These commands work to generate a binary that is faster due to PGO: mkdir bld cd bld cmake -DWITHOUT_PERFSCHEMA_STORAGE_ENGINE=1 -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_C_FLAGS_RELWITHDEBINFO="-Wno-maybe-uninitialized -g -O3 --coverage" -DCMAKE_CXX_FLAGS_RELWITHDEBINFO="-Wno-maybe-uninitialized -g -O3 --coverage" .. make tests/gen_profile_load cmake -DWITHOUT_PERFSCHEMA_STORAGE_ENGINE=1 -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_C_FLAGS_RELWITHDEBINFO="-Wno-maybe-uninitialized -g -O3 -fprofile-use -fprofile-correction" -DCMAKE_CXX_FLAGS_RELWITHDEBINFO="-Wno-maybe-uninitialized -g -O3 -fprofile-use -fprofile-correction" make So all the pieces really are there, it should be possible to implement it. But we need to find a good way to integrate it into our build system. The best would be to integrate it into our cmake files. The gen_profile_load.c could go into tests/, ideally we would build both a static and dynamically linked version (so we get PGO for both libmysqlclient.a and libmysqlclient.so). Anyone can help me get cmake to do that? And it would be cool if we could get the above procedure to work completely within cmake, so that the user could just do: cmake -DWITH_PGO ... ; make and cmake would itself handle first building with --coverage, then running gen_profile_load.static and gen_profile_load.dynamic, then rebuilding with -fprofile-use. Anyone know if this is possible with cmake, and if so could help implement it? But alternatively, we could integrate a double build, like the commands above, into the buildbot scripts (.deb, .rpm, bintar). Any comments? Here are some more points: - I tested that gen_profile_load gives a good speedup of sysbench read-only (around 30%, so still very significant even though it generates a different and more varied load). - As another test, I removed all SELECT from gen_profile_load, and ran the resulting PGO binary with sysbench read-only. This still gave a fair speedup, despite the PGO load being completely different from the benchmark load. This gives me confidence that the PGO should not cause performance regressions in cases not covered well by gen_profile_load - More tests would be nice, of course. Axel, would you be able to build some binaries following above procedure, and test some different random benchmarks? Anything that is easy to run could be interesting, both to test for improvement, and to check against regressions. - We probably need a recent GCC version to get good results. I used GCC version 4.7.2. Maybe we should install this GCC version in all the VMs we use to build binaries? - Should we do this in 5.5? I think we might want to. The speedup is quite significant, and it seems very safe - no code modifications are involved, only different compiler options. Any thoughts? Volunteeres for helping with the cmake or buildbot parts? - Kristian.

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[Maria-developers] valgrind failure in main.statistics
by Sergey Petrunia 29 Apr '14

29 Apr '14

Hello Igor, Valgrind build in buildbot currently fails in main.statistics test: http://buildbot.askmonty.org/buildbot/builders/work-amd64-valgrind/builds/5… I have tracked it down: the failure appeared after this push by you: revno: 4157 [merge] committer: Igor Babaev <igor(a)askmonty.org> branch nick: maria-10.0 timestamp: Tue 2014-04-22 14:43:13 -0700 message: Merge. ------------------------------------------------------------ revno: 4152.1.1 committer: Igor Babaev <igor(a)askmonty.org> branch nick: maria-10.0-bugs timestamp: Tue 2014-04-22 14:39:57 -0700 message: Fixed the problem of mdev-5947. Back-ported from the mysql 5.6 code line the patch with the following comment: Fix for Bug#11757108 CHANGE IN EXECUTION PLAN FOR COUNT_DISTINCT_GROUP_ON_KEY CAUSES PEFORMANCE REGRESSION I suppose it would take you much less time than anybody else to fix this? The failure is not repeatable on every machine: it doesn't repeat on my machines, but it can be repeated on work.askmonty.org. BR Sergei -- Sergei Petrunia, Software Developer MariaDB | Skype: sergefp | Blog: http://s.petrunia.net/blog

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