From 93997a8b8e66da7a1a62411eda4a845f6c0ec781 Mon Sep 17 00:00:00 2001
From: Pascal Seitz <pascal.seitz@gmail.com>
Date: Tue, 18 May 2021 09:55:31 +0200
Subject: [PATCH] use itertools groupby, fix serialization test

---
 src/indexer/index_writer.rs     |  2 +-
 src/indexer/log_merge_policy.rs | 41 ++++++++++++++++-----------------
 2 files changed, 21 insertions(+), 22 deletions(-)

diff --git a/src/indexer/index_writer.rs b/src/indexer/index_writer.rs
index dee4fefbc6..718f5203f1 100644
--- a/src/indexer/index_writer.rs
+++ b/src/indexer/index_writer.rs
@@ -945,7 +945,7 @@ mod tests {
         let index_writer = index.writer(3_000_000).unwrap();
         assert_eq!(
             format!("{:?}", index_writer.get_merge_policy()),
-            "LogMergePolicy { min_merge_size: 8, max_merge_size: 10000000, min_layer_size: 10000, \
+            "LogMergePolicy { min_num_segments: 8, max_docs_before_merge: 10000000, min_layer_size: 10000, \
              level_log_size: 0.75 }"
         );
         let merge_policy = Box::new(NoMergePolicy::default());
diff --git a/src/indexer/log_merge_policy.rs b/src/indexer/log_merge_policy.rs
index 12b7b3edf4..68345aee78 100644
--- a/src/indexer/log_merge_policy.rs
+++ b/src/indexer/log_merge_policy.rs
@@ -1,5 +1,6 @@
 use super::merge_policy::{MergeCandidate, MergePolicy};
 use crate::core::SegmentMeta;
+use itertools::Itertools;
 use std::cmp;
 use std::f64;
 
@@ -65,29 +66,27 @@ impl MergePolicy for LogMergePolicy {
         }
         size_sorted_segments.sort_by_key(|seg| std::cmp::Reverse(seg.num_docs()));
 
-        let sorted_segments_with_log_size: Vec<_> = size_sorted_segments
-            .into_iter()
-            .map(|seg| (seg, f64::from(self.clip_min_size(seg.num_docs())).log2()))
-            .collect();
-
-        if let Some(&(largest_segment, log_size)) = sorted_segments_with_log_size.first() {
-            let mut current_max_log_size = log_size;
-            let mut levels = vec![vec![largest_segment]];
-            for &(segment, segment_log_size) in sorted_segments_with_log_size.iter().skip(1) {
-                if segment_log_size < (current_max_log_size - self.level_log_size) {
-                    current_max_log_size = segment_log_size;
-                    levels.push(Vec::new());
-                }
-                levels.last_mut().unwrap().push(segment);
+        let mut current_max_log_size = f64::MAX;
+        let mut levels = vec![];
+        for (_, merge_group) in &size_sorted_segments.into_iter().group_by(|segment| {
+            let segment_log_size = f64::from(self.clip_min_size(segment.num_docs())).log2();
+            if segment_log_size < (current_max_log_size - self.level_log_size) {
+                // update current_max_log_size to create a new group
+                current_max_log_size = segment_log_size;
+                current_max_log_size
+            } else {
+                // return current_max_log_size to be grouped to the current group
+                current_max_log_size
             }
-            levels
-                .iter()
-                .filter(|level| level.len() >= self.min_num_segments)
-                .map(|segments| MergeCandidate(segments.iter().map(|&seg| seg.id()).collect()))
-                .collect()
-        } else {
-            return vec![];
+        }) {
+            levels.push(merge_group.collect::<Vec<&SegmentMeta>>());
         }
+
+        levels
+            .iter()
+            .filter(|level| level.len() >= self.min_num_segments)
+            .map(|segments| MergeCandidate(segments.iter().map(|&seg| seg.id()).collect()))
+            .collect()
     }
 }