Implement efficient clearing of the Hashtable #106
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Bobobalink
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This allows us to directly find the bucket that points to each value in the value array, which makes erasing elements given an iterator faster (before we needed one key lookup for each element erased). Practically, this makes clearing large "chunks" of the FixedMap faster.
Bobobalink
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Instead of iterating over the linked list (also requires hash lookups) and erasing one by one, just reset the backing linked list and value storage, then 0 out the bucket array.
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Bobobalink
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Apr 12, 2024
| @@ -190,10 +209,20 @@ class FixedRobinhoodHashtable | |||
| // until we hit an empty one | |||
| while (0 != bucket_at(table_loc).dist_and_fingerprint_) | |||
| { | |||
| // update the backlink of the value pointed to by the bucket we're about to put in | |||
| // table_loc | |||
| bucket_for_value_index(bucket.value_index_) = table_loc; | |||
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this is actually quite a lot of extra work that is required for every single insertion and deletion. We expect there to be a lot of buckets that need to be moved, and now each of those moves also requires touching this separate array.
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Instead of iterating over the linked list (also requires hash lookups) and erasing one by one, just reset the backing linked list and value storage, then 0 out the bucket array.