Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
New issue
Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.
Already on GitHub? Sign in to your account
[hashset feature] Scan shortcut fix #1217
base: hashset
Are you sure you want to change the base?
[hashset feature] Scan shortcut fix #1217
Changes from all commits
3879c1b
9bf0c39
File filter
Filter by extension
Conversations
Jump to
There are no files selected for viewing
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Computing this requires a memory access that's not useful in the growing case. Growing is normally the most performance sensitive situation.
My guess is that it's cheaper to check it only when we need it...
On the other hand, the previous bucket has most likely been rehashed just before, so it's in the L1 cache already. Anyway, I'm not sure if one is better than the other.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Hmm, good point. I realized we only actually need to check when we're first starting a rehash - in all other cases we know that we ended rehashStep with a bucket without
everfull
set :)There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
With this change, I guess there's a small increased risk of returning duplicates.
Time 1:
SCAN 0
returned new cursor 8.Time 2:
SCAN 8
.SCAN 8
returns elements from small table bucket 0 (masked with small table mask) and large table bucket 8 (masked with large table mask). Large table bucket 0 can safely be skipped.SCAN 8
returns elements from small table bucket 0 (masked with small table mask) and large table bucket 0 and 8 (expansion of cursor masked with small table mask).There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Hmm, I see! Yes, that makes sense. I think it'll be fixed if I don't modify
cursor
here and instead apply the masks tostart_cursor
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Yes, maybe. But it doesn't matter much, especially if we want to change probing to chaining anyway... Let's not spend too much effort on this.