01cdba9a98
This series attempts to get read of flakiness in `cache_algorithm_test` by solving two problems. Problem 1: The test needs to create some arbitrary partition keys of a given size. It intends to create keys of the form: 0x0000000000000000000000000000000000000000... 0x0100000000000000000000000000000000000000... 0x0200000000000000000000000000000000000000... But instead, unintentionally, it creates partially initialized keys of the form: 0x0000000000000000garbagegarbagegarbagegar... 0x0100000000000000garbagegarbagegarbagegar... 0x0200000000000000garbagegarbagegarbagegar... Each of these keys is created several times and -- for the test to pass -- the result must be the same each time. By coincidence, this is usually the case, since the same allocator slots are used. But if some background task happens to overwrite the allocator slot during a preemption, the keys used during "SELECT" will be different than the keys used during "INSERT", and the test will fail due to extra cache misses. Problem 2: Cache stats are global, so there's no good way to reliably verify that e.g. a given read causes 0 cache misses, because something done by Scylla in a background can trigger a cache miss. This can cause the test to fail spuriously. With how the test framework and the cache are designed, there's probably no good way to test this properly. It would require ensuring that cache stats are per-read, or at least per-table, and that Scylla's background activity doesn't cause enough memory pressure to evict the tested rows. This patch tries to deal with the flakiness without deleting the test altogether by letting it retry after a failure if it notices that it can be explained by a read which wasn't done by the test. (Though, if the test can't be written well, maybe it just shouldn't be written...) Fixes #21536 Should be backported to prevent flaky failures in older branches. Closes scylladb/scylladb#21948 * github.com:scylladb/scylladb: cache_algorithm_test: harden against stats being confused by background activity cache_algorithm_test: fix a use of an uninitialized variable
Scylla unit tests using C++ and the Boost test framework
The source files in this directory are Scylla unit tests written in C++ using the Boost.Test framework. These unit tests come in three flavors:
-
Some simple tests that check stand-alone C++ functions or classes use Boost's
BOOST_AUTO_TEST_CASE. -
Some tests require Seastar features, and need to be declared with Seastar's extensions to Boost.Test, namely
SEASTAR_TEST_CASE. -
Even more elaborate tests require not just a functioning Seastar environment but also a complete (or partial) Scylla environment. Those tests use the
do_with_cql_env()ordo_with_cql_env_thread()function to set up a mostly-functioning environment behaving like a single-node Scylla, in which the test can run.
While we have many tests of the third flavor, writing new tests of this type should be reserved to white box tests - tests where it is necessary to inspect or control Scylla internals that do not have user-facing APIs such as CQL. In contrast, black-box tests - tests that can be written only using user-facing APIs, should be written in one of newer test frameworks that we offer - such as test/cqlpy or test/alternator (in Python, using the CQL or DynamoDB APIs respectively) or test/cql (using textual CQL commands), or - if more than one Scylla node is needed for a test - using the test/topology* framework.
Running tests
Because these are C++ tests, they need to be compiled before running.
To compile a single test executable row_cache_test, use a command like
ninja build/dev/test/boost/row_cache_test
You can also use ninja dev-test to build all C++ tests, or use
ninja deb-build to build the C++ tests and also the full Scylla executable
(however, note that full Scylla executable isn't needed to run Boost tests).
Replace "dev" by "debug" or "release" in the examples above and below to use the "debug" build mode (which, importantly, compiles the test with ASAN and UBSAN enabling on and helps catch difficult-to-catch use-after-free bugs) or the "release" build mode (optimized for run speed).
To run an entire test file row_cache_test, including all its test
functions, use a command like:
build/dev/test/boost/row_cache_test -- -c1 -m1G
to run a single test function test_reproduce_18045() from the longer test
file, use a command like:
build/dev/test/boost/row_cache_test -t test_reproduce_18045 -- -c1 -m1G
In these command lines, the parameters before the -- are passed to
Boost.Test, while the parameters after the -- are passed to the test code,
and in particular to Seastar. In this example Seastar is asked to run on one
CPU (-c1) and use 1G of memory (-m1G) instead of hogging the entire
machine. The Boost.Test option -t test_reproduce_18045 asks it to run just
this one test function instead of all the test functions in the executable.
Unfortunately, interrupting a running test with control-C while doesn't
work. This is a known bug (#5696). Kill a test with SIGKILL (-9) if you
need to kill it while it's running.
Boost tests can also be run using test.py - which is a script that provides a uniform way to run all tests in scylladb.git - C++ tests, Python tests, etc.
Writing tests
Because of the large build time and build size of each separate test executable, it is recommended to put test functions into relatively large source files. But not too large - to keep compilation time of a single source file (during development) at reasonable levels.
When adding new source files in test/boost, don't forget to list the new source file in configure.py and also in CMakeLists.txt. The former is needed by our CI, but the latter is preferred by some developers.