feat: Make MaxThreads None by default

crates/meilisearch/src/lib.rs

@@ -504,18 +504,22 @@ fn import_dump(
     let network = dump_reader.network()?.cloned().unwrap_or_default();
     index_scheduler.put_network(network)?;
 
-    let mut indexer_config = index_scheduler.indexer_config().clone_no_threadpool();
-
-    // 3.1 Use all cpus to index the import dump
-    indexer_config.thread_pool = {
-        let all_cpus = num_cpus::get();
-
-        let temp_pool = ThreadPoolNoAbortBuilder::new()
-            .thread_name(|index| format!("indexing-thread:{index}"))
-            .num_threads(all_cpus)
-            .build()?;
-
-        Some(temp_pool)
+    // 3.1 Use all cpus to process dump if max_indexing_threads not configured
+    let backup_config;
+    let indexer_config = if index_scheduler.indexer_config().max_threads.is_none() {
+        let mut _config = index_scheduler.indexer_config().clone_no_threadpool();
+        _config.thread_pool = {
+            Some(
+                ThreadPoolNoAbortBuilder::new()
+                    .thread_name(|index| format!("indexing-thread:{index}"))
+                    .num_threads(num_cpus::get())
+                    .build()?,
+            )
+        };
+        backup_config = _config;
+        &backup_config
+    } else {
+        index_scheduler.indexer_config()
     };
 
     // /!\ The tasks must be imported AFTER importing the indexes or else the scheduler might
@@ -533,7 +537,7 @@ fn import_dump(
 
         let mut wtxn = index.write_txn()?;
 
-        let mut builder = milli::update::Settings::new(&mut wtxn, &index, &indexer_config);
+        let mut builder = milli::update::Settings::new(&mut wtxn, &index, indexer_config);
         // 4.1 Import the primary key if there is one.
         if let Some(ref primary_key) = metadata.primary_key {
             builder.set_primary_key(primary_key.to_string());
@@ -568,7 +572,7 @@ fn import_dump(
         let builder = milli::update::IndexDocuments::new(
             &mut wtxn,
             &index,
-            &indexer_config,
+            indexer_config,
             IndexDocumentsConfig {
                 update_method: IndexDocumentsMethod::ReplaceDocuments,
                 ..Default::default()

crates/meilisearch/src/option.rs

@@ -746,10 +746,12 @@ impl IndexerOpts {
                 max_indexing_memory.to_string(),
             );
         }
-        export_to_env_if_not_present(
-            MEILI_MAX_INDEXING_THREADS,
-            max_indexing_threads.0.to_string(),
-        );
+        if let Some(max_indexing_threads) = max_indexing_threads.0 {
+            export_to_env_if_not_present(
+                MEILI_MAX_INDEXING_THREADS,
+                max_indexing_threads.to_string(),
+            );
+        }
     }
 }
 
@@ -757,14 +759,18 @@ impl TryFrom<&IndexerOpts> for IndexerConfig {
     type Error = anyhow::Error;
 
     fn try_from(other: &IndexerOpts) -> Result<Self, Self::Error> {
+        // use 1/2 cpu threads if no value specified
+        let max_indexing_threads = other.max_indexing_threads.unwrap_or(num_cpus::get() / 2);
+
         let thread_pool = ThreadPoolNoAbortBuilder::new()
             .thread_name(|index| format!("indexing-thread:{index}"))
-            .num_threads(*other.max_indexing_threads)
+            .num_threads(max_indexing_threads)
             .build()?;
 
         Ok(Self {
             log_every_n: Some(DEFAULT_LOG_EVERY_N),
             max_memory: other.max_indexing_memory.map(|b| b.as_u64() as usize),
+            max_threads: *other.max_indexing_threads,
             thread_pool: Some(thread_pool),
             max_positions_per_attributes: None,
             skip_index_budget: other.skip_index_budget,
@@ -828,31 +834,31 @@ fn total_memory_bytes() -> Option<u64> {
     }
 }
 
-#[derive(Debug, Clone, Copy, Deserialize, Serialize)]
-pub struct MaxThreads(usize);
+#[derive(Default, Debug, Clone, Copy, Deserialize, Serialize)]
+pub struct MaxThreads(Option<usize>);
 
 impl FromStr for MaxThreads {
     type Err = ParseIntError;
 
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        usize::from_str(s).map(Self)
-    }
-}
-
-impl Default for MaxThreads {
-    fn default() -> Self {
-        MaxThreads(num_cpus::get() / 2)
+    fn from_str(s: &str) -> Result<MaxThreads, Self::Err> {
+        if s.is_empty() {
+            return Ok(MaxThreads::default());
+        }
+        usize::from_str(s).map(Some).map(MaxThreads)
     }
 }
 
 impl fmt::Display for MaxThreads {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{}", self.0)
+        match self.0 {
+            Some(threads) => write!(f, "{}", threads),
+            None => Ok(()),
+        }
     }
 }
 
 impl Deref for MaxThreads {
-    type Target = usize;
+    type Target = Option<usize>;
 
     fn deref(&self) -> &Self::Target {
         &self.0