Go: runtime: opportunistically rotate map key seed
As further protection, when the size of a non-tiny map drops to zero, we should update its hash seed. This is a reminder issue.
See discussion in CL 110055.
cc @martisch @randall77
josharian
All 6 comments
Just curious: why not do the same when map growing is initiated? Is there something preventing the new/bigger map storage to use a different seed?
CAFxX
on 4 May 2018
The way we grow the map, it isn't possible. Each original bucket evacuates to just two new buckets. The hashes need to agree on all the common bits.
There might be other growing algorithms where it could work.
randall77
on 4 May 2018
Punting to unplanned. Pretty low priority.
randall77
on 28 Dec 2018
Change https://golang.org/cl/253020 mentions this issue: runtime: opportunistically rotate map key seed
gopherbot
on 3 Sep 2020
While https://golang.org/cl/253020 resets the seed when the map clear idiom is used it doesnt reset the seed when maps are emptied to zero elements by just deleting elements without ranging over all the keys or when the pattern for map clear is not triggered. I think this is done in map clear we should also do it on deleting if an element is deleted and the maps length drops to 0.
martisch
on 4 Sep 2020
Change https://golang.org/cl/252940 mentions this issue: runtime: rotate map key seed when delete last element
gopherbot
on 4 Sep 2020
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Most helpful comment
While https://golang.org/cl/253020 resets the seed when the map clear idiom is used it doesnt reset the seed when maps are emptied to zero elements by just deleting elements without ranging over all the keys or when the pattern for map clear is not triggered. I think this is done in map clear we should also do it on deleting if an element is deleted and the maps length drops to 0.