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optimize word prefix fst

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ad hoc 2022-03-15 15:56:07 +01:00
parent 290a29b5fb
commit d68fe2b3c7
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GPG Key ID: 4F00A782990CC643
1 changed files with 20 additions and 19 deletions
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35
milli/src/update/words_prefixes_fst.rs
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@ -1,7 +1,6 @@
use std::iter::FromIterator;
use std::str;
use fst::Streamer;
use fst::{SetBuilder, Streamer};
use crate::{Index, Result, SmallString32};
@ -44,43 +43,45 @@ impl<'t, 'u, 'i> WordsPrefixesFst<'t, 'u, 'i> {
pub fn execute(self) -> Result<()> {
let words_fst = self.index.words_fst(&self.wtxn)?;
let mut prefix_fsts = Vec::with_capacity(self.max_prefix_length);
for n in 1..=self.max_prefix_length {
let mut current_prefix = SmallString32::new();
let mut current_prefix_count = 0;
let mut builder = fst::SetBuilder::memory();
let mut current_prefix = vec![SmallString32::new(); self.max_prefix_length];
let mut current_prefix_count = vec![0; self.max_prefix_length];
let mut builders: Vec<_> =
std::iter::repeat_with(SetBuilder::memory).take(self.max_prefix_length).collect();
let mut stream = words_fst.stream();
while let Some(bytes) = stream.next() {
for n in 0..self.max_prefix_length {
let current_prefix = &mut current_prefix[n];
let current_prefix_count = &mut current_prefix_count[n];
let builder = &mut builders[n];
// We try to get the first n bytes out of this string but we only want
// to split at valid characters bounds. If we try to split in the middle of
// a character we ignore this word and go to the next one.
let word = str::from_utf8(bytes)?;
let prefix = match word.get(..n) {
let word = std::str::from_utf8(bytes)?;
let prefix = match word.get(..=n) {
Some(prefix) => prefix,
None => continue,
};
// This is the first iteration of the loop,
// or the current word doesn't starts with the current prefix.
if current_prefix_count == 0 || prefix != current_prefix.as_str() {
current_prefix = SmallString32::from(prefix);
current_prefix_count = 0;
if *current_prefix_count == 0 || prefix != current_prefix.as_str() {
*current_prefix = SmallString32::from(prefix);
*current_prefix_count = 0;
}
current_prefix_count += 1;
*current_prefix_count += 1;
// There is enough words corresponding to this prefix to add it to the cache.
if current_prefix_count >= self.threshold {
if *current_prefix_count >= self.threshold {
builder.insert(prefix)?;
}
}
// We construct the final set for prefixes of size n.
prefix_fsts.push(builder.into_set());
}
// We merge all of the previously computed prefixes into on final set.
let prefix_fsts: Vec<_> = builders.into_iter().map(|sb| sb.into_set()).collect();
let op = fst::set::OpBuilder::from_iter(prefix_fsts.iter());
let mut builder = fst::SetBuilder::memory();
builder.extend_stream(op.r#union())?;