rabbit_khepri: Optimize cleanup in topic binding projection (backport #15214)#15237
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rabbit_khepri: Optimize cleanup in topic binding projection (backport #15214)#15237
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[Why] Before this patch, the projection function that managed the topic bindings graph only kept track of "topic word -> topic word" = "this node ID". Reading and updating this graph was efficient. However, deleting a node in this graph was expensive because it used `ets:match/3` to determine if an edge was pointing to nothing and could be reclaimed. `ets:match()` does a full scan of the table. On my laptop, this scan took 20 ms with 100k topic bindings, thus >30 minutes to delete all of them. [How] The new projection function tracks the number of children a target node has as well. This way, it knows that if this counter reaches 0, the edge can be reclaimed. The same test with 100k topic bindings takes 3.5 seconds to delete them. (cherry picked from commit 612d93d)
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Why
Before this patch, the projection function that managed the topic bindings graph only kept track of "topic word -> topic word" = "this node ID". Reading and updating this graph was efficient.
However, deleting a node in this graph was expensive because it used
ets:match/3to determine if an edge was pointing to nothing and could be reclaimed.ets:match()does a full scan of the table. On my laptop, this scan took 20 ms with 100k topic bindings, thus >30 minutes to delete all of them.How
The new projection function tracks the number of children a target node has as well. This way, it knows that if this counter reaches 0, the edge can be reclaimed.
The same test with 100k topic bindings takes 3.5 seconds to delete them.
This is an automatic backport of pull request #15214 done by Mergify.