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Type: Improvement
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Resolution: Unresolved
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Priority: Major - P3
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None
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Affects Version/s: None
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Component/s: APIs
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Storage Engines
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StorEng - Defined Pipeline
Random cursors behave poorly in workloads that have many deletions. This ticket points out some of the anomalies and some potential fixes and/or improvements. Part of of random iteration code includes code that selects a random leaf page. As eviction uses this same random leaf selection, some improvements here may help with eviction for these workloads.
These workloads may not be uncommon at all. Consider a collection that contains orders being processed. An order comes in, a new order is created. When the order is fulfilled, it is removed from this collection, maybe moved to a different collection of past orders. If the key is always advancing, then over time get a tree with lots of pages that have no entries, or few entries.
In the comments will be a program that does a simple simulation of this situation and the surprising results of testing random cursors on this.
It's possible that multiple smaller tickets will spin off of this investigation.