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Emitting both a short term average and a long term average of shard (#…
…5202) * Emitting both a short term average and a long term average of shard throughput. Scaling up relies on the short term average in order to rapidly react to a change in throughput, while scaling down and the indexing scheduler relies on the long term average. * added comment
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quickwit/quickwit-control-plane/src/ingest/scaling_arbiter.rs
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| // Copyright (C) 2024 Quickwit, Inc. | ||
| // | ||
| // Quickwit is offered under the AGPL v3.0 and as commercial software. | ||
| // For commercial licensing, contact us at [email protected]. | ||
| // | ||
| // AGPL: | ||
| // This program is free software: you can redistribute it and/or modify | ||
| // it under the terms of the GNU Affero General Public License as | ||
| // published by the Free Software Foundation, either version 3 of the | ||
| // License, or (at your option) any later version. | ||
| // | ||
| // This program is distributed in the hope that it will be useful, | ||
| // but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| // GNU Affero General Public License for more details. | ||
| // | ||
| // You should have received a copy of the GNU Affero General Public License | ||
| // along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
|
|
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| use crate::model::{ScalingMode, ShardStats}; | ||
|
|
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| pub(crate) struct ScalingArbiter { | ||
| // Threshold in MiB/s below which we decrease the number of shards. | ||
| scale_down_shards_threshold_mib_per_sec: f32, | ||
|
|
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| // Threshold in MiB/s above which we increase the number of shards. | ||
| // In order to make scaling up reactive, the decision is mostly taken by inspecting the short | ||
| // term threshold. | ||
| // | ||
| // However, this threshold is based on a very short window of time: 5s. | ||
| // | ||
| // In order to avoid having back and forth scaling up and down in response to temporary | ||
| // punctual spikes of a few MB, we also compute what would be the long term ingestion rate | ||
| // after scaling up, and double check that it is above the long term threshold. | ||
| scale_up_shards_short_term_threshold_mib_per_sec: f32, | ||
| scale_up_shards_long_term_threshold_mib_per_sec: f32, | ||
| } | ||
|
|
||
| impl ScalingArbiter { | ||
| pub fn with_max_shard_ingestion_throughput_mib_per_sec( | ||
| max_shard_throughput_mib_per_sec: f32, | ||
| ) -> ScalingArbiter { | ||
| ScalingArbiter { | ||
| scale_up_shards_short_term_threshold_mib_per_sec: max_shard_throughput_mib_per_sec | ||
| * 0.8f32, | ||
| scale_up_shards_long_term_threshold_mib_per_sec: max_shard_throughput_mib_per_sec | ||
| * 0.3f32, | ||
| scale_down_shards_threshold_mib_per_sec: max_shard_throughput_mib_per_sec * 0.2f32, | ||
| } | ||
| } | ||
|
|
||
| pub(crate) fn should_scale(&self, shard_stats: ShardStats) -> Option<ScalingMode> { | ||
| // We scale up based on the short term threshold to scale up more aggressively. | ||
| if shard_stats.avg_short_term_ingestion_rate | ||
| >= self.scale_up_shards_short_term_threshold_mib_per_sec | ||
| { | ||
| let long_term_ingestion_rate_after_scale_up = shard_stats.avg_long_term_ingestion_rate | ||
| * (shard_stats.num_open_shards as f32) | ||
| / (shard_stats.num_open_shards as f32 + 1.0f32); | ||
| if long_term_ingestion_rate_after_scale_up | ||
| >= self.scale_up_shards_long_term_threshold_mib_per_sec | ||
| { | ||
| return Some(ScalingMode::Up); | ||
| } | ||
| } | ||
|
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| // On the other hand, we scale down based on the long term ingestion rate, to avoid | ||
| // scaling down just due to a very short drop in ingestion | ||
| if shard_stats.avg_long_term_ingestion_rate <= self.scale_down_shards_threshold_mib_per_sec | ||
| && shard_stats.num_open_shards > 1 | ||
| { | ||
| return Some(ScalingMode::Down); | ||
| } | ||
|
|
||
| None | ||
| } | ||
| } | ||
|
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||
| #[cfg(test)] | ||
| mod tests { | ||
| use super::ScalingArbiter; | ||
| use crate::model::{ScalingMode, ShardStats}; | ||
|
|
||
| #[test] | ||
| fn test_scaling_arbiter() { | ||
| let scaling_arbiter = ScalingArbiter::with_max_shard_ingestion_throughput_mib_per_sec(10.0); | ||
| assert_eq!( | ||
| scaling_arbiter.should_scale(ShardStats { | ||
| num_open_shards: 1, | ||
| avg_short_term_ingestion_rate: 5.0, | ||
| avg_long_term_ingestion_rate: 6.0, | ||
| }), | ||
| None | ||
| ); | ||
| assert_eq!( | ||
| scaling_arbiter.should_scale(ShardStats { | ||
| num_open_shards: 1, | ||
| avg_short_term_ingestion_rate: 8.1, | ||
| avg_long_term_ingestion_rate: 8.1, | ||
| }), | ||
| Some(ScalingMode::Up) | ||
| ); | ||
| assert_eq!( | ||
| scaling_arbiter.should_scale(ShardStats { | ||
| num_open_shards: 2, | ||
| avg_short_term_ingestion_rate: 3.0, | ||
| avg_long_term_ingestion_rate: 1.5, | ||
| }), | ||
| Some(ScalingMode::Down) | ||
| ); | ||
| assert_eq!( | ||
| scaling_arbiter.should_scale(ShardStats { | ||
| num_open_shards: 1, | ||
| avg_short_term_ingestion_rate: 3.0, | ||
| avg_long_term_ingestion_rate: 1.5, | ||
| }), | ||
| None, | ||
| ); | ||
| assert_eq!( | ||
| scaling_arbiter.should_scale(ShardStats { | ||
| num_open_shards: 1, | ||
| avg_short_term_ingestion_rate: 8.0f32, | ||
| avg_long_term_ingestion_rate: 3.0f32, | ||
| }), | ||
| None, | ||
| ); | ||
| } | ||
| } |
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