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...)
Fixesscylladb/scylladb#21536
(cherry picked from commit 1fffd976a4)
(cherry picked from commit 6caaead4ac)
Parent PR: scylladb/scylladb#21948Closesscylladb/scylladb#22228
* 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
ef93c3a8d7