There may be some problems with MySQL when testing parallel writes in
different non-committing transactions, even in READ COMMITTED mode,
due to InnoDB locking, if the queries use non-unique secondary indexes
for UPDATE or SELECT..FOR UPDATE queries. This is done by the
"with_lockmode('update')" SQLAlchemy phrase, and is used in ~10 places
in Nova. So I would not recommend this approach, even though, in
principle, I agree it would be a much more efficient way of testing
database reads/writes.More details here: http://dev.mysql.com/doc/refman/5.5/en/innodb-locks-set.html and http://dev.mysql.com/doc/refman/5.5/en/innodb-record-level-locks.html On Sun, Jun 8, 2014 at 8:46 AM, Roman Podoliaka <rpodoly...@mirantis.com> wrote: > Hi Mike, > >>>> However, when testing an application that uses a fixed set of tables, as >>>> should be the case for the majority if not all Openstack apps, there’s no >>>> reason that these tables need to be recreated for every test. > > This is a very good point. I tried to use the recipe from SQLAlchemy > docs to run Nova DB API tests (yeah, I know, this might sound > confusing, but these are actually methods that access the database in > Nova) on production backends (MySQL and PostgreSQL). The abandoned > patch is here [1]. Julia Varlamova has been working on rebasing this > on master and should upload a new patch set soon. > > Overall, the approach with executing a test within a transaction and > then emitting ROLLBACK worked quite well. The only problem I ran into > were tests doing ROLLBACK on purpose. But you've updated the recipe > since then and this can probably be solved by using of save points. I > used a separate DB per a test running process to prevent race > conditions, but we should definitely give READ COMMITTED approach a > try. If it works, that will awesome. > > With a few tweaks of PostgreSQL config I was able to run Nova DB API > tests in 13-15 seconds, while SQLite in memory took about 7s. > > Action items for me and Julia probably: [2] needs a spec with [1] > updated accordingly. Using of this 'test in a transaction' approach > seems to be a way to go for running all db related tests except the > ones using DDL statements (as any DDL statement commits the current > transaction implicitly on MySQL and SQLite AFAIK). > > Thanks, > Roman > > [1] https://review.openstack.org/#/c/33236/ > [2] https://blueprints.launchpad.net/nova/+spec/db-api-tests-on-all-backends > > On Sat, Jun 7, 2014 at 10:27 PM, Mike Bayer <mba...@redhat.com> wrote: >> >> On Jun 6, 2014, at 8:12 PM, Devananda van der Veen <devananda....@gmail.com> >> wrote: >> >> I think some things are broken in the oslo-incubator db migration code. >> >> Ironic moved to this when Juno opened and things seemed fine, until recently >> when Lucas tried to add a DB migration and noticed that it didn't run... So >> I looked into it a bit today. Below are my findings. >> >> Firstly, I filed this bug and proposed a fix, because I think that tests >> that don't run any code should not report that they passed -- they should >> report that they were skipped. >> https://bugs.launchpad.net/oslo/+bug/1327397 >> "No notice given when db migrations are not run due to missing engine" >> >> Then, I edited the test_migrations.conf file appropriately for my local >> mysql service, ran the tests again, and verified that migration tests ran -- >> and they passed. Great! >> >> Now, a little background... Ironic's TestMigrations class inherits from >> oslo's BaseMigrationTestCase, then "opportunistically" checks each back-end, >> if it's available. This opportunistic checking was inherited from Nova so >> that tests could pass on developer workstations where not all backends are >> present (eg, I have mysql installed, but not postgres), and still >> transparently run on all backends in the gate. I couldn't find such >> opportunistic testing in the oslo db migration test code, unfortunately - >> but maybe it's well hidden. >> >> Anyhow. When I stopped the local mysql service (leaving the configuration >> unchanged), I expected the tests to be skipped, but instead I got two >> surprise failures: >> - test_mysql_opportunistically() failed because setUp() raises an exception >> before the test code could call calling _have_mysql() >> - test_mysql_connect_fail() actually failed! Again, because setUp() raises >> an exception before running the test itself >> >> Unfortunately, there's one more problem... when I run the tests in parallel, >> they fail randomly because sometimes two test threads run different >> migration tests, and the setUp() for one thread (remember, it calls >> _reset_databases) blows up the other test. >> >> Out of 10 runs, it failed three times, each with different errors: >> NoSuchTableError: `chassis` >> ERROR 1007 (HY000) at line 1: Can't create database 'test_migrations'; >> database exists >> ProgrammingError: (ProgrammingError) (1146, "Table >> 'test_migrations.alembic_version' doesn't exist") >> >> As far as I can tell, this is all coming from: >> >> https://github.com/openstack/oslo-incubator/blob/master/openstack/common/db/sqlalchemy/test_migrations.py#L86;L111 >> >> >> Hello - >> >> Just an introduction, I’m Mike Bayer, the creator of SQLAlchemy and Alembic >> migrations. I’ve just joined on as a full time Openstack contributor, >> and trying to help improve processes such as these is my primary >> responsibility. >> >> I’ve had several conversations already about how migrations are run within >> test suites in various openstack projects. I’m kind of surprised by this >> approach of dropping and recreating the whole database for individual tests. >> Running tests in parallel is obviously made very difficult by this style, >> but even beyond that, a lot of databases don’t respond well to lots of >> dropping/rebuilding of tables and/or databases in any case; while SQLite and >> MySQL are probably the most forgiving of this, a backend like Postgresql is >> going to lock tables from being dropped more aggressively, if any open >> transactions or result cursors against those tables remain, and on a backend >> like Oracle, the speed of schema operations starts to become prohibitively >> slow. Dropping and creating tables is in general not a very speedy task on >> any backend, and on a test suite that runs many tests against a fixed >> schema, I don’t see why a full drop is necessary. >> >> If you look at SQLAlchemy’s own tests, they do in fact create tables on each >> test, or just as often for a specific suite of tests. However, this is due >> to the fact that SQLAlchemy tests are testing SQLAlchemy itself, so the >> database schemas used for these tests are typically built explicitly for >> small groups or individual tests, and there are ultimately thousands of >> small “mini schemas” built up and torn down for these tests. A lot of >> framework code is involved within the test suite to keep more picky >> databases like Postgresql and Oracle happy when building up and dropping >> tables so frequently. >> >> However, when testing an application that uses a fixed set of tables, as >> should be the case for the majority if not all Openstack apps, there’s no >> reason that these tables need to be recreated for every test. Typically, >> the way I recommend is that the test suite includes a “per suite” activity >> which creates the test schema just once (with or without using CREATE >> DATABASE; I’m not a fan of tests running CREATE DATABASE as this is not a >> command so easily available in some environments). The tests themselves >> then run within a transactional container, such that each test performs all >> of its work within a context that doesn’t actually commit any data to the >> database; a test that actually states “session.commit()” runs within a >> container that doesn’t actually emit the COMMIT, and if support is needed >> for tests that also emit “session.rollback()”, the container can be written >> to support this paradigm as well (I helped some Dropbox devs with such an >> approach recently). >> >> In this way, the database migrations are exercised, but only once at the >> beginning in order to build up the schema; the tests can then run with very >> low complexity/performance overhead as far as database-level setup/teardown, >> and parallel testing is also much easier. When the test suite completes is >> when a drop of the entire set of tables can proceed. Because tests are run >> within transactions, assuming READ COMMITTED isolation is established, the >> tests don’t even see the data being incurred by other tests running in >> parallel. >> >> It remains to be seen what aspects of Openstack I’m going to get involved >> with first, though this migration and testing issue seems to be a big one. >> I’d love to get comments from the community here as to how this process >> might be improved and if a rearrangement of the fixture system in the way I >> describe might be helpful and feasible. >> >> - mike >> >> >> >> _______________________________________________ >> OpenStack-dev mailing list >> OpenStack-dev@lists.openstack.org >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev >> > > _______________________________________________ > OpenStack-dev mailing list > OpenStack-dev@lists.openstack.org > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev _______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
