[DOCS-9441] Docs for SERVER-26579: Sharding balancer moves chunks to shards whose utilization is above the cluster average Created: 02/Dec/16 Updated: 30/Oct/23 Resolved: 17/Mar/23 |
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| Status: | Closed |
| Project: | Documentation |
| Component/s: | Server |
| Affects Version/s: | None |
| Fix Version/s: | Server_Docs_20231030 |
| Type: | Task | Priority: | Major - P3 |
| Reporter: | Emily Hall | Assignee: | Ravind Kumar (Inactive) |
| Resolution: | Won't Do | Votes: | 0 |
| Labels: | DF | ||
| Remaining Estimate: | Not Specified | ||
| Time Spent: | Not Specified | ||
| Original Estimate: | Not Specified | ||
| Issue Links: |
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| Participants: | |||||||||
| Days since reply: | 46 weeks, 6 days ago | ||||||||
| Description |
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Engineering Ticket Description: The current sharding balancer policy attempts to move chunks from shards which have more than the cluster-wide per-shard chunk count average to shards which have less than it. However there is a bug due to which chunks will move from highly loaded to less-loaded shard if the difference between the two is sufficiently large. In particular consider the following case:
Intuitively, this should produce only two migrations: Shard1 -> Shard5 and Shard2 -> Shard 6. However it will also cause a third migration from Shard3 -> Shard4, because 900 is above the ideal per-shard chunk number of 600. Via kaloian.manassiev |
| Comments |
| Comment by Sarah Olson [ 17/Mar/23 ] |
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Closing this out on the grounds that:
Based on this, closing as WON'T DO. Please don't hesitate to give me a shout or to reopen if you disagree. |
| Comment by Kaloian Manassiev [ 31/Dec/16 ] |
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The balancer has no means to look into the "read/write utilization" - it only deals with number of chunks and estimated size of the chunk, using the formula that you pointed out. With The second bulled above is correct. |
| Comment by Ravind Kumar (Inactive) [ 02/Dec/16 ] |
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kaloian.manassiev I don't quite follow what has been resolved here. From the summary and your comment, I think the change overall is that the balancer can move chunks off of a shard if either
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