tustvold commented on code in PR #2393:
URL: https://github.com/apache/arrow-rs/pull/2393#discussion_r943187558
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parquet/src/encodings/decoding.rs:
##########
@@ -736,8 +736,47 @@ where
}
fn skip(&mut self, num_values: usize) -> Result<usize> {
- let mut buffer = vec![T::T::default(); num_values];
- self.get(&mut buffer)
+ let mut skip = 0;
+ let to_skip = num_values.min(self.values_left);
+ if to_skip == 0 {
+ return Ok(0);
+ }
+
+ // try to consume first value in header.
+ if let Some(value) = self.first_value.take() {
+ self.last_value = value;
+ skip += 1;
+ self.values_left -= 1;
+ }
+
+ while skip != to_skip {
+ if self.mini_block_remaining == 0 {
+ self.next_mini_block()?;
+ }
+
+ let bit_width = self.mini_block_bit_widths[self.mini_block_idx] as
usize;
+ let batch_to_skip = self.mini_block_remaining.min(to_skip - skip);
+
+ for i in 0..batch_to_skip {
+ if let Some(v) = self.bit_reader.get_value::<T::T>(bit_width) {
+ self.last_value = self
Review Comment:
Effectively you can only skip efficiently in multiples of the block size, as
otherwise you are still having to decode all the value
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