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Use Intersect to Narrow Iterate Range and Reduce Memory Allocation #9271

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Use Intersect to Narrow Iterate Range and Reduce Memory Allocation #9271

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3b23c92
Use Intersect to Narrow Iterate Range and Reduce Memory Allocation
Jan 9, 2025
25a8814
Use Intersect to Narrow Iterate Range and Reduce Memory Allocation
Jan 10, 2025
a5576a1
Use Intersect to Narrow Iterate Range and Reduce Memory Allocation
Jan 10, 2025
17d0349
Use Intersect to Narrow Iterate Range and Reduce Memory Allocation
Jan 10, 2025
2121ec2
Use Intersect to Narrow Iterate Range and Reduce Memory Allocation
Jan 13, 2025
5516de8
Use Intersect to Narrow Iterate Range and Reduce Memory Allocation
Jan 13, 2025
f25dfee
handle negative opt.First
Jan 15, 2025
0d023b0
Use native min function to replace custom implementation
Jan 17, 2025
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64 changes: 54 additions & 10 deletions posting/list.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1672,10 +1672,8 @@ func (l *List) Uids(opt ListOptions) (*pb.List, error) {
if opt.First == 0 {
opt.First = math.MaxInt32
}
// Pre-assign length to make it faster.
l.RLock()
// Use approximate length for initial capacity.
res := make([]uint64, 0, l.mutationMap.len()+codec.ApproxLen(l.plist.Pack))

out := &pb.List{}
if l.mutationMap.len() == 0 && opt.Intersect != nil && len(l.plist.Splits) == 0 {
if opt.ReadTs < l.minTs {
Expand All @@ -1687,16 +1685,62 @@ func (l *List) Uids(opt ListOptions) (*pb.List, error) {
return out, nil
}

absFirst := opt.First
if opt.First < 0 {
absFirst = -opt.First
}
preAllowcateLength := min(absFirst, l.mutationMap.len()+codec.ApproxLen(l.plist.Pack))
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@harshil-goel harshil-goel Jan 20, 2025 •
edited
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I think we have a function for it (getting approx len)

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Also the actual length could be way more for some postings (split postings). Lets use the exact length function here. It would only hurt in case of split postings. We can resolve that later.

if opt.Intersect != nil {
preAllowcateLength = min(preAllowcateLength, len(opt.Intersect.Uids))
}
// Pre-assign length to make it faster.
res := make([]uint64, 0, preAllowcateLength)

checkLimit := func() bool {
// We need the last N.
// TODO: This could be optimized by only considering some of the last UidBlocks.
if opt.First < 0 {
if len(res) > -opt.First {
res = res[1:]
}
} else if len(res) > opt.First {
return true
}
return false
}

if opt.Intersect != nil && len(opt.Intersect.Uids) < l.mutationMap.len()+codec.ApproxLen(l.plist.Pack) {
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same: use exact length.
lets create another function inside list that intersects with the list of uids.

start := 0
if opt.AfterUid > 0 {
start = sort.Search(len(opt.Intersect.Uids), func(i int) bool {
return opt.Intersect.Uids[i] > opt.AfterUid
})
}

for i := start; i < len(opt.Intersect.Uids); i++ {
uid := opt.Intersect.Uids[i]

found, _, err := l.findPosting(opt.ReadTs, uid)
if err != nil {
l.RUnlock()
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Instead of manually calling RUnlock() each time a return happens, you could do defer l.RUnlock() at the start of the function for the same effect.

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Instead of manually calling RUnlock() each time a return happens, you could do defer l.RUnlock() at the start of the function for the same effect.

When implementing this code, I also considered making this change, but I referred to the previous implementation and believe it was designed to minimize the time spent holding the read lock. Therefore, I chose not to change this implementation.

return out, errors.Wrapf(err, "While find posting for UIDs")
}
if found {
res = append(res, uid)
if checkLimit() {
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instead of checking for negative first here like this, why not just check the ids in reverse.

break
}
}
}
out.Uids = res
l.RUnlock()
return out, nil
}

err := l.iterate(opt.ReadTs, opt.AfterUid, func(p *pb.Posting) error {
if p.PostingType == pb.Posting_REF {
res = append(res, p.Uid)
if opt.First < 0 {
// We need the last N.
// TODO: This could be optimized by only considering some of the last UidBlocks.
if len(res) > -opt.First {
res = res[1:]
}
} else if len(res) > opt.First {
if checkLimit() {
return ErrStopIteration
}
}
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