1d06ea3a5a
Currently if raft is enabled all nodes are voters in group0. However it is not necessary to have all nodes to be voters - it only slows down the raft group operation (since the quorum is large) and makes deployments with asymmetrical DCs problematic (2 DCs with 5 nodes along 1 DC with 10 nodes will lose the majority if large DC is isolated). The topology coordinator will now maintain a state where there are only limited number of voters, evenly distributed across the DCs and racks. After each node addition or removal the voters are recalculated and rebalanced if necessary. That means: * When a new node is added, it might become a voter depending on the current distribution of voters - either if there are still some voter "slots" available, or if the new node is a better candidate than some existing voter (in which case the existing node voter status might be revoked). * When a voter node is removed or stopped (shut down), its voter status is revoked and another node might become a voter instead (this can also depend on other circumstances, like e.g. changing the number of DCs). * If a node addition or removal causes a change in number of datacenters (DCs) or racks, the rebalance action might become wider (as there are some special rules applying to 1 vs 2 vs more DCs, also changing the number of racks might cause similar effects in the voters distribution) Special conditions for various number of DCs: * 1 DC: Can have up to the maximum allowed number of voters (5 - see below) * 2 DCs: The distribution of the voters will be asymmetric (if possible), meaning that we can tolerate a loss of the DC with the smaller number of voters (if both would have the same number of voters we'd lose the majority if any of the DCs is lost). For example, if we have 2 DCs with 2 nodes each, one of them will only have 1 voter (despite the limit of 5). Also, if one of the 2 DCs has more racks than the other and the node count allows it, the DC with the more racks will have more voters. * 3 and more DCs: The distribution of the voters will be so that every DC has strictly less than half of the total voters (so a loss of any of the DCs cannot lead to the majority loss). Again, DCs with more racks are being preferred in the voter distribution. At the moment we will be handling the zero-token nodes in the same way as the regular nodes (i.e. the zero-token nodes will not take any priority in the voter distribution). Technically it doesn't make much sense to have a zero-token node that is not a voter (when there are regular nodes in the same DC being voters), but currently the intended purpose of zero-token nodes is to form an "arbiter DC" (in case of 2 DCs, creating a third DC with zero-token nodes only), so for that intended purpose no special handling is needed and will work out of the box. If a preference of zero token nodes will eventually be needed/requested, it will be added separately from this PR. Currently the voter limits will not be configurable (we might introduce configurable limits later if that would be needed/requested). The feature is enabled by the `group0_limited_voters` feature flag to avoid issues with cluster upgrade (the feature will be only enabled once all nodes in the cluster are upgraded to the version supporting the feature). Fixes: scylladb/scylladb#18793
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.