On Jun 9, 2014, at 1:08 PM, Mike Bayer <mba...@redhat.com> wrote:
>
> On Jun 9, 2014, at 12:50 PM, Devananda van der Veen <devananda....@gmail.com>
> wrote:
>
>> 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
>
> OK, but just to clarify my understanding, what is the approach to testing
> writes in parallel right now, are we doing CREATE DATABASE for two entirely
> distinct databases with some kind of generated name for each one? Otherwise,
> if the parallel tests are against the same database, this issue exists
> regardless (unless autocommit mode is used, is FOR UPDATE accepted under
> those conditions?)
Took a look and this seems to be the case, from oslo.db:
def create_database(engine):
"""Provide temporary user and database for each particular test."""
driver = engine.name
auth = {
'database': ''.join(random.choice(string.ascii_lowercase)
for i in moves.range(10)),
# ...
sqls = [
"drop database if exists %(database)s;",
"create database %(database)s;"
]
Just thinking out loud here, I’ll move these ideas to a new wiki page after
this post. My idea now is that OK, we provide ad-hoc databases for tests,
but look into the idea that we create N ad-hoc databases, corresponding to
parallel test runs - e.g. if we are running five tests concurrently, we make
five databases. Tests that use a database will be dished out among this pool
of available schemas. In the *typical* case (which means not the case that
we’re testing actual migrations, that’s a special case) we build up the schema
on each database via migrations or even create_all() just once, run tests
within rolled-back transactions one-per-database, then the DBs are torn down
when the suite is finished.
Sorry for the thread hijack.
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