kvserver: introduce cpu rebalancing #95152
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Previously `Queries` was hardcoded as the dimension to use when creating test ranges for use in store rebalancer tests. This patch enables passing in any `dimension`. Release note: None
Previously, when estimating the impact a lease transfer would have, we would not differentiate between rebalance/transfer. This commit adds a utility method `TransferImpact` to `RangeUsageInfo` which is now used when making estimations about lease transers. Currently, this is identical to `Load`, which was previously used instead for transfers. Release note: None
This patch allows the store rebalancer to use CPU in place of QPS when balancing load on a cluster. This patch adds `cpu` as an option with the cluster setting: `kv.allocator.load_based_rebalancing.objective` When set to `cpu`, rather than `qps`. The store rebalancer will perform a mostly identical function, however target balancing the sum of all replica's cpu time on each store, rather than qps. The default remains as `qps` here. Similar to QPS, the rebalance threshold can be set to allow controlling the range above and below the mean store CPU is considered imbalanced, either overfull or underfull respectively: `kv.allocator.cpu_rebalance_threshold`: 0.1 In order to manage with mixed versions during upgrade and some architectures not supporting the cpu sampling method, a rebalance objective manager is introduced in `rebalance_objective.go`. The manager mediates access to the rebalance objective and overwrites it in cases where the objective set in the cluster setting cannot be supported. resolves: cockroachdb#95380 Release note (ops change) Add option to balance cpu time (cpu) instead of queries per second (qps) among stores in a cluster. This is done by setting `kv.allocator.load_based_rebalancing.objective='cpu'`. `kv.allocator.cpu_rebalance_threshold` is also added, similar to `kv.allocator.qps_rebalance_threshold` to control the target range for store cpu above and below the cluster mean.
This patch removes the deprecated 'lastSplitQPS' value throughout the split/merge code. This field was deprecated in 22.1 in favor or `maxSplitQPS` and stopped being consulted in 22.2. Now only `maxSplitQPS` is consulted and set in `RangeStatsResponse`. Release note: None
This commit adds the ability to peform load based splitting with replica cpu usage rather than queries per second. Load based splitting now will use either cpu or qps for deciding split points, depending on the cluster setting `kv.allocator.load_based_rebalancing.objective`. When set to `qps`, qps is used in deciding split points and when splitting should occur; similarly, `cpu` means that request cpu against the leasholder replica is to decide split points. The split threshold when using `cpu` is the cluster setting `kv.range_split.load_cpu_threshold` which defaults to `250ms` of cpu time per second, i.e. a replica using 1/4 processor of a machine consistently. The merge queue uses the load based splitter to make decisions on whether to merge two adjacent ranges due to low load. This commit also updates the merge queue to be consistent with the load based splitter signal. When switching between `qps` and `cpu`, the load based splitter for every replica is reset to avoid spurious results. resolves: cockroachdb#95377 Release note (ops change): Load based splitter now supports using request cpu usage to split ranges. This is introduced with the previous cluster setting `kv.allocator.load_based_rebalancing.objective`, which when set to `cpu`, will use request cpu usage. The threshold above which CPU usage of a range is considered for splitting is defined in the cluster setting `kv.range_split.load_cpu_threshold`, which has a default value of `250ms`.
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This series of commits introduces using CPU as a replacement for QPS in rebalancing and splitting.
The results when using CPU in comparison to QPS can be found here (internal).
CPU load based rebalancing and splitting is not enabled by default in this PR.
resolves: #95380
resolves: #95377