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This is a step towards more flexibility in managing tablets. A prerequisite before we can split individual tablets, isolating hot partitions, and evening-out tablet sizes by shifting boundaries. After this patch, the system can handle tables with arbitrary tablet count. Tablet allocator is still rounding up desired tablet count to the nearest power of two when allocating tablets for a new table, so unless the tablet map is allocated in some other way, the counts will be still a power of two. We plan to utilize arbitrary count when migrating from vnodes to tablets, by creating a tablet map which matches vnode boundaries. One of the reasons we don't give up on power-of-two by default yet is that it creates an issue with merges. If tablet count is odd, one of the tablets doesn't have a sibling and will not be merged. That can obviously cause imbalance of token space and tablet sizes between tablets. To limit the impact, this patch dynamically chooses which tablet to isolate when initiating a merge. The largest tablet is chosen, as that will minimize imbalance. Otherwise, if we always chose the last tablet to isolate, its size would remain the same while other tablets double in size with each odd-count merge, leading to imbalance. The imbalance will still be there, but the difference in tablet sizes is limited to 2x. Example (3 tablets): [0] owns 1/3 of tokens [1] owns 1/3 of tokens [2] owns 1/3 of tokens After merge: [0] owns 2/3 of tokens [1] owns 1/3 of tokens What we would like instead: Step 1 (split [1]): [0] owns 1/3 of tokens [1] old 1.left, owns 1/6 of tokens [2] old 1.right, owns 1/6 of tokens [3] owns 1/3 of tokens Step 2 (merge): [0] owns 1/2 of tokens [1] owns 1/2 of tokens To do that, we need to be able to split individual tablets, but we're not there yet.
Scylla in-source tests.
For details on how to run the tests, see docs/dev/testing.md
Shared C++ utils, libraries are in lib/, for Python - pylib/
alternator - Python tests which connect to a single server and use the DynamoDB API unit, boost, raft - unit tests in C++ cqlpy - Python tests which connect to a single server and use CQL topology* - tests that set up clusters and add/remove nodes cql - approval tests that use CQL and pre-recorded output rest_api - tests for Scylla REST API Port 9000 scylla-gdb - tests for scylla-gdb.py helper script nodetool - tests for C++ implementation of nodetool
If you can use an existing folder, consider adding your test to it. New folders should be used for new large categories/subsystems, or when the test environment is significantly different from some existing suite, e.g. you plan to start scylladb with different configuration, and you intend to add many tests and would like them to reuse an existing Scylla cluster (clusters can be reused for tests within the same folder).
To add a new folder, create a new directory, and then
copy & edit its suite.ini.