From d19c8672bb66eaf6405ca726f6b6eaa0021ea61c Mon Sep 17 00:00:00 2001
From: Gregory Conrad <gregorysconrad@gmail.com>
Date: Wed, 23 Nov 2022 15:50:53 -0500
Subject: [PATCH] perf: limit reindex to when exact_attributes changes

---
 milli/src/index.rs           |  5 ++---
 milli/src/update/settings.rs | 23 ++++++++++++++++-------
 2 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/milli/src/index.rs b/milli/src/index.rs
index 5910a305c..d9636634d 100644
--- a/milli/src/index.rs
+++ b/milli/src/index.rs
@@ -1145,9 +1145,8 @@ impl Index {
     }
 
     /// Clears the exact attributes from the store.
-    pub(crate) fn delete_exact_attributes(&self, txn: &mut RwTxn) -> Result<()> {
-        self.main.delete::<_, Str>(txn, main_key::EXACT_ATTRIBUTES)?;
-        Ok(())
+    pub(crate) fn delete_exact_attributes(&self, txn: &mut RwTxn) -> Result<bool> {
+        Ok(self.main.delete::<_, Str>(txn, main_key::EXACT_ATTRIBUTES)?)
     }
 
     pub fn max_values_per_facet(&self, txn: &RoTxn) -> heed::Result<Option<usize>> {
diff --git a/milli/src/update/settings.rs b/milli/src/update/settings.rs
index 6da32d73f..8220ed3ab 100644
--- a/milli/src/update/settings.rs
+++ b/milli/src/update/settings.rs
@@ -465,14 +465,23 @@ impl<'a, 't, 'u, 'i> Settings<'a, 't, 'u, 'i> {
     fn update_exact_attributes(&mut self) -> Result<bool> {
         match self.exact_attributes {
             Setting::Set(ref attrs) => {
-                let attrs = attrs.iter().map(String::as_str).collect::<Vec<_>>();
-                self.index.put_exact_attributes(self.wtxn, &attrs)?;
-                Ok(true)
-            }
-            Setting::Reset => {
-                self.index.delete_exact_attributes(self.wtxn)?;
-                Ok(true)
+                let old_attrs = self
+                    .index
+                    .exact_attributes(self.wtxn)?
+                    .iter()
+                    .cloned()
+                    .map(String::from)
+                    .collect::<HashSet<String>>();
+
+                if attrs != &old_attrs {
+                    let attrs = attrs.iter().map(String::as_str).collect::<Vec<_>>();
+                    self.index.put_exact_attributes(self.wtxn, &attrs)?;
+                    Ok(true)
+                } else {
+                    Ok(false)
+                }
             }
+            Setting::Reset => Ok(self.index.delete_exact_attributes(self.wtxn)?),
             Setting::NotSet => Ok(false),
         }
     }