[SERVER-46435] Alternatives to using the lookaside-score for snapshot (history) window control [v4.2 only] Created: 26/Feb/20 Updated: 06/Dec/22 Resolved: 01/Feb/21 |
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| Status: | Closed |
| Project: | Core Server |
| Component/s: | Storage |
| Affects Version/s: | None |
| Fix Version/s: | None |
| Type: | Task | Priority: | Major - P3 |
| Reporter: | Dianna Hohensee (Inactive) | Assignee: | Backlog - Storage Execution Team |
| Resolution: | Won't Do | Votes: | 0 |
| Labels: | None | ||
| Remaining Estimate: | Not Specified | ||
| Time Spent: | Not Specified | ||
| Original Estimate: | Not Specified | ||
| Issue Links: |
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| Assigned Teams: |
Storage Execution
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| Sprint: | Execution Team 2020-03-23, Execution Team 2020-04-20 | ||||||||||||||||
| Participants: | |||||||||||||||||
| Description |
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A few potential solutions I can think of: |
| Comments |
| Comment by Connie Chen [ 01/Feb/21 ] | |||||||
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We would be potentially destabilizing 4.2 with this change, closing as won't do. | |||||||
| Comment by Dianna Hohensee (Inactive) [ 06/May/20 ] | |||||||
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The WT eviction_trigger configuration defaults to 95% and is when application threads start to perform eviction. At that point, performance is starting to suffer / become unreliable. WT also has an eviction_target configuration that defaults to 80% at which it tries to keep the cache fullness. WT eviction threads are active when this threshold is reached. So WT seems to try to keep the cache relatively full, so that reads are fast, I imagine. WT also has an eviction_dirty_target (default 5%) and eviction_dirty_trigger (default 20%). These behave similarly and can co-opt application threads for eviction. I've been looking at the information here http://source.wiredtiger.com/3.2.1/tune_cache.html to conclude the above. ------------------------------------------------------------------------------- Two potential solutions I can think of: | |||||||
| Comment by Dianna Hohensee (Inactive) [ 08/Apr/20 ] | |||||||
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Lookaside table inserts are not logically going to work because insert frequency could drop while cache pressure remains high. And it is thought (unconfirmed) that inserts can occur before there's any significant cache pressure. Luke Pearson suggested these metrics:
So I'll look into them. | |||||||
| Comment by Connie Chen [ 27/Feb/20 ] | |||||||
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Ensure to confirm with WT that this is change is correct |