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feat: skip invisible row for chunk::get_hash_values #15696

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merged 7 commits into from
Mar 18, 2024

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@st1page st1page commented Mar 14, 2024

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What's changed and what's your intention?

link #14985 #15251

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for i in self.visibility().iter_ones() {
// SAFETY(value_at_unchecked): the idx is always in bound.
unsafe {
if let Some(scalar) = col.value_at_unchecked(i) {
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Want to make sure there is no branch instruction?

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yes, and iter_ones() optimize traversing bitmap with bit operator.

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@fuyufjh fuyufjh Mar 18, 2024

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I am afraid iter_ones() is still too heavy (see BitmapOnesIter). That's why I proposed #15696 (comment)

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fuyufjh commented Mar 18, 2024

A few alternative approaches to make it more "vectorized" which I think worth taking a try:

  1. Replace visibility Bitmap with visibility Vec<usize>. This is because for idx in vec is more vectorized i.e. no branches at all so more friendly to CPU pipeline.
  2. Similar to 1 but only do it for low-selectivity cases
  3. Do compaction before exchange, because we know exchange will always produce low-selectivity results.

@st1page st1page added this pull request to the merge queue Mar 18, 2024
Merged via the queue into main with commit a9bdaa8 Mar 18, 2024
33 of 34 checks passed
@st1page st1page deleted the sts/skip_invisible_row_for_chunk_get_hash_values branch March 18, 2024 03:25
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4 participants