[SERVER-25652] Slow chunk migrations when there are large chunk counts. 3.0, 3.2, 3.3.11 Created: 17/Aug/16 Updated: 31/Oct/16 Resolved: 27/Oct/16 |
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| Status: | Closed |
| Project: | Core Server |
| Component/s: | Sharding |
| Affects Version/s: | 3.0.8, 3.3.11 |
| Fix Version/s: | None |
| Type: | Bug | Priority: | Major - P3 |
| Reporter: | Akira Kurogane | Assignee: | Kaloian Manassiev |
| Resolution: | Duplicate | Votes: | 0 |
| Labels: | None | ||
| Remaining Estimate: | Not Specified | ||
| Time Spent: | Not Specified | ||
| Original Estimate: | Not Specified | ||
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| Operating System: | ALL | ||||||||||||||||||||||||
| Steps To Reproduce: |
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| Sprint: | Sharding 2016-09-19, Sharding 2016-10-10, Sharding 2016-10-31 | ||||||||||||||||||||||||
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| Description |
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I've been testing the speed of chunk migrations in an all-on-one-server test cluster. Even when the chunks being migrated are empty (i.e. the chunk move takes only ~0.1 secs) the entire cycle run by the balancer takes a lot longer.
From someone's else case with v3.2 and different servers / network to my test I heard of a ~6 second cycle. Not sure if that was a replica set config db or the older SCCC-style one. Can the balancer be changed so that the balance round will do multiple chunks of each collection so long as they finish quickly? E.g. balance round identifies candidate chunks for migrations, and keeps on doing chunk moves for them serially until a, say, 10 sec window completes. At any rate if data has been completely deleted for a big fraction of chunk ranges before adding a new shard, it would be good if those chunks moves happened a lot more quickly. |
| Comments |
| Comment by Kaloian Manassiev [ 27/Oct/16 ] |
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There are multiple aspects of the chunk migration process which contribute to the speed of migration in the case where there are no documents in the chunks and these have been isolated in the related tickets. This ticket will be closed in lieu of these more specific tickets. |
| Comment by Dianna Hohensee (Inactive) [ 19/Aug/16 ] |
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Okay, no problem. I'm not sure exactly when we'll start testing, so if you get a chance, great, if we get there first, that's fine too. Thanks again for the JS you did attach. |