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keep allocations as small as possible #306

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merged 3 commits into from
Jan 6, 2021
Merged

keep allocations as small as possible #306

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b0fd355
keep allocations as small as possible
bblanton-asapp Jan 6, 2021
9fb59a0
add a little more byte padding
bblanton-asapp Jan 6, 2021
6dbb4dd
suggested change
bblanton-asapp Jan 6, 2021
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10 changes: 6 additions & 4 deletions zstd/seqdec.go
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Original file line number Diff line number Diff line change
Expand Up @@ -181,11 +181,13 @@ func (s *sequenceDecs) decode(seqs int, br *bitReader, hist []byte) error {
return fmt.Errorf("output (%d) bigger than max block size", size)
}
if size > cap(s.out) {
// Not enough size, will be extremely rarely triggered,
// Not enough size, which can happen under high volume block streaming conditions
// but could be if destination slice is too small for sync operations.
// We add maxBlockSize to the capacity.
s.out = append(s.out, make([]byte, maxBlockSize)...)
s.out = s.out[:len(s.out)-maxBlockSize]
// over-allocating here can create a large amount of GC pressure so we try to keep
// it as contained as possible
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addBytes := 1024 + (size - len(s.out))
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Suggested change
addBytes := 1024 + (size - len(s.out))
used := len(s.out) - startSize
addBytes := 256 + ll + ml + used>>2
// Clamp to max block size.
if used+addBytes > maxBlockSize {
addBytes = maxBlockSize - used
}

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Maybe something like this?

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ok gave that change a whirl
there's about a 500-750Mb difference in the ram usage, higher using method, then the original size - len one, but it does seem to not get out of control, which is the desired effect.

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Great. I will merge when Ci tests are done and probably release it tomorrow.

s.out = append(s.out, make([]byte, addBytes)...)
s.out = s.out[:len(s.out)-addBytes]
}
if ml > maxMatchLen {
return fmt.Errorf("match len (%d) bigger than max allowed length", ml)
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