[SERVER-24833] Certain queries are 2000x time slower with WiredTiger than with MMAPv1 Created: 29/Jun/16 Updated: 04/Oct/16 Resolved: 03/Oct/16 |
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| Status: | Closed |
| Project: | Core Server |
| Component/s: | WiredTiger |
| Affects Version/s: | 3.2.7 |
| Fix Version/s: | None |
| Type: | Bug | Priority: | Major - P3 |
| Reporter: | Edgar Costa | Assignee: | Kelsey Schubert |
| Resolution: | Cannot Reproduce | Votes: | 3 |
| Labels: | None | ||
| Remaining Estimate: | Not Specified | ||
| Time Spent: | Not Specified | ||
| Original Estimate: | Not Specified | ||
| Attachments: |
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| Operating System: | ALL | ||||||||||||
| Steps To Reproduce: |
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| Description |
| Comments |
| Comment by Kelsey Schubert [ 03/Oct/16 ] | |||||||||||||||||||||
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Hi edgarcosta, We have not been able to reproduce this issue. I see that in your logs after the WiredTiger cache is hot, the query takes ~600ms to complete. As you know, MMAPv1 relies on the filesystem cache, whereas WiredTiger utilizes both its own cache and the filesystem cache. This difference may explain the results you are observing. Kind regards, | |||||||||||||||||||||
| Comment by Edgar Costa [ 01/Jul/16 ] | |||||||||||||||||||||
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Thank you. Also, I did these experiments on a "n1-highmem-4" machine from google compute engine, i.e., 4 cpu with 26 GB of memory.
I have attached ticket.tar where:
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| Comment by Kelsey Schubert [ 29/Jun/16 ] | |||||||||||||||||||||
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Hi edgarcosta, Thank you for opening this ticket. I've downloaded the dataset and ran the same query twice on WiredTiger with default configuration (first run with the cache empty, the second run with the cache hot). When the cache was empty it took 14 seconds, with the cache hot it took 0.2 seconds to complete. The performance is on the same order of magnitude for MMAPv1. Please see the logs of the queries below. WiredTiger:
MMAPv1:
To continue to investigate this issue, would you please archive (tar or zip) the $dbpath/diagnostic.data directory and attach it to this ticket for both the WiredTiger and MMAPv1 nodes? Thank you, |