Increase target shard usage #5771
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rdettai
commented
May 20, 2025
| * 0.3f32, | ||
| scale_down_shards_threshold_mib_per_sec: max_shard_throughput_mib_per_sec * 0.2f32, | ||
| * 0.375f32, | ||
| scale_down_shards_threshold_mib_per_sec: max_shard_throughput_mib_per_sec * 0.25f32, | ||
| shard_scale_up_factor, |
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Increase the target load by 25% only. Increasing it more would prevent the scaling from 1 shard to 2 shards to happen properly. Take max_shard_throughput_mib_per_sec=5MB and num_open_shards=1:
- with 0.3 as scale up load factor,
scale_up_shards_long_term_threshold_mib_per_sec=1.5MB. This means thatavg_long_term_ingestion_ratemust be >3MB for scaling event to occur. - with 0.375 as scale up load factor,
scale_up_shards_long_term_threshold_mib_per_sec=1.875MB. This means thatavg_long_term_ingestion_ratemust be >3.75MB for scaling event to occur. - with 0.45 as scale up load factor,
scale_up_shards_long_term_threshold_mib_per_sec=2.25MB. This means thatavg_long_term_ingestion_ratemust be >4.5MB for scaling event to occur.
This is due to how long_term_scale_up_threshold_max_shards avoids getting into the interval [scale_down, scale_up]
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Description
Currently the target shard usage before scaling down the number of shards is 20%. This is quite low which results in a high number of shards.
Also decrease the default scale up factor from 1.5 to 1.1. A scale up factor of 1.1 still exhibits a good scaling behavior for bigger indexes (e.g shards are added 10 by 10 when an index has 100 shards) while limiting the likelihood of overshooting.
How was this PR tested?
Added unit tests.