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This patch adds a simple proof-of-concept test framework, and a few tests, for the random query generator, specifically the portion of the random query generator that is responsible for taking a Query object and doing something with it. The two pieces of functionality I chose for exhibition are 1. Writing the query into Impala SQL 2. Reporting characteristics in the SELECT clause (used internally) In the interest of keeping the patch small, I have not added many tests, nor have I chose to focus on more areas for test. On its own this is fairly simple. As I add features to this portion of the query generator, though, it will be more useful to test new functionality and also regression test the framework. Change-Id: I2ed1960430ae0af469986e33f88aecb6fa74e999 Reviewed-on: http://gerrit.cloudera.org:8080/4081 Reviewed-by: Michael Brown <mikeb@cloudera.com> Reviewed-by: Matthew Jacobs <mj@cloudera.com> Tested-by: Internal Jenkins
Purpose:
This package is intended to augment the standard test suite. The standard tests are
more efficient with regards to features tested versus execution time. However their
coverage as a test suite still leaves gaps in query coverage. This package provides a
random query generator to compare the results of a wide range of queries against a
reference database engine. The queries will range from very simple single table selects to
extremely complicated with multiple level of nesting. This method of testing will be
slower but has a larger coverage area.
Requirements:
1) It's assumed that Impala is running locally.
2) Impyla -- an implementation of DB API 2 for Impala.
sudo pip install impyla
3) At least one python driver for a reference database.
sudo apt-get install python-mysqldb
sudo apt-get install python-psycopg2 # Postgresql
Please see the supplemental ORACLE.txt on setting up Oracle as a reference
database.
Usage:
1) Generate test data
./data_generator.py --use-postgresql
This will generate tables and data in Postgresql and Impala
2) Run the comparison
./discrepancy_searcher.py
This will generate queries using the test database and compare the results against
Postgresql (the default).
Things to Know:
1) A good number of queries to run seems to be about 5k. Ideally each test run would
discover the complete list of known issues. From experience a 1k query test run may
complete without finding any issues that were discovered in previous runs. 5k seems
to be about the magic number were most issues will be rediscovered. This can take 1-2
hours. However as of this writing it's rare to run 1k queries without finding at
least one discrepancy.
2) It's possible to provide a randomization seed so that the randomness is actually
reproducible. The data generation currently has a default seed so will always produce
the same tables. This also mean if a new data type is added those generated tables
will change.
3) There is a query log. It's possible that a sequence of queries is required to expose
a bug. If you come across a failure that can't be reproduced by rerunning the failed
query, try running the queries leading up to that query as well.
Miscellaneous:
1) Instead of generating new random queries with each run, it may be better to reuse a
list of queries from a previous run that are known to produce results. As of this
writing only about 50% of queries produce results. So it may be better to trade high
randomness for higher quality queries. For example it would be possible to build up a
library of 100k queries that produce results then randomly select 2.5k of those.
Maybe that would provide testing equivalent to 5k totally random queries in less
time.
This would also be useful in eliminating queries that have known issues above.
Postgresql:
1) Supports basically all Impala language features. Exceptions include:
a) IGNORE NULLS clause for analytic functions
2) Has strange sorting of strings, '-1' > '1'. This may be important if ORDER BY is ever
used. The databases being compared would need to have the same collation, which is
probably configurable.
MySQL:
1) Does not support analytics.
2) Has poor boolean support.
Oracle:
1) No Boolean support.
2) Better analytic function support, e.g. "IGNORE NULLS" is supported.
3) Strange oddities abound, like no LIMIT clause.
Improvements:
1) Add the ability to incrementally increase the complexity of query profiles
automatically during execution. For example, the profile could start with no joins,
then after 100 or so queries, the number of joins could be increased. This would
lead to bugs that are not related to joins being found by much simpler queries.
2) Add support for simplifying buggy queries. When a random query fails the comparison
check it is basically always much too complex for directly posting a bug report. It
is also time consuming to simplify the queries because there is a lot of trial and
error and manually editing queries.
3) Add common built-in functions. Ex: NVL, ...
4) Add support for comparing results with codegen enabled and disabled. Uri recently added
support for query options in Impyla.