Merge #2830

2830: Increase max concurrent readers on indexes r=irevoire a=arriven

# Pull Request

## What does this PR do?
Fixes #2786 
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## PR checklist
Please check if your PR fulfills the following requirements:
- [x] Does this PR fix an existing issue?
- [x] Have you read the contributing guidelines?
- [x] Have you made sure that the title is accurate and descriptive of the changes?

Thank you so much for contributing to Meilisearch!


Co-authored-by: arriven <20084245+Arriven@users.noreply.github.com>

meilisearch-lib/src/index/dump.rs

@@ -105,6 +105,7 @@ impl Index {
 
         let mut options = EnvOpenOptions::new();
         options.map_size(size);
+        options.max_readers(1024);
         let index = milli::Index::new(options, &dst_dir_path)?;
 
         let mut txn = index.write_txn()?;

meilisearch-lib/src/index/index.rs

@@ -94,6 +94,7 @@ impl Index {
         create_dir_all(&path)?;
         let mut options = EnvOpenOptions::new();
         options.map_size(size);
+        options.max_readers(1024);
         let inner = Arc::new(milli::Index::new(options, &path)?);
         Ok(Index {
             inner,

meilisearch-lib/src/snapshot.rs

@@ -181,6 +181,7 @@ impl SnapshotJob {
 
             let mut options = milli::heed::EnvOpenOptions::new();
             options.map_size(self.index_size);
+            options.max_readers(1024);
             let index = milli::Index::new(options, entry.path())?;
             index.copy_to_path(dst, CompactionOption::Enabled)?;
         }