Implement the index compaction task

crates/index-scheduler/src/processing.rs

@@ -138,6 +138,16 @@ make_enum_progress! {
     }
 }
 
+make_enum_progress! {
+    pub enum IndexCompaction {
+        RetrieveTheIndex,
+        CreateTemporaryFile,
+        CopyAndCompactTheIndex,
+        PersistTheCompactedIndex,
+        CloseTheIndex,
+    }
+}
+
 make_enum_progress! {
     pub enum InnerSwappingTwoIndexes {
         RetrieveTheTasks,

crates/index-scheduler/src/scheduler/process_batch.rs

@@ -1,22 +1,26 @@
 use std::collections::{BTreeSet, HashMap, HashSet};
+use std::io::{Seek, SeekFrom};
 use std::panic::{catch_unwind, AssertUnwindSafe};
 use std::sync::atomic::Ordering;
 
+use byte_unit::Byte;
 use meilisearch_types::batches::{BatchEnqueuedAt, BatchId};
 use meilisearch_types::heed::{RoTxn, RwTxn};
+use meilisearch_types::milli::heed::CompactionOption;
 use meilisearch_types::milli::progress::{Progress, VariableNameStep};
 use meilisearch_types::milli::{self, ChannelCongestion};
 use meilisearch_types::tasks::{Details, IndexSwap, Kind, KindWithContent, Status, Task};
 use meilisearch_types::versioning::{VERSION_MAJOR, VERSION_MINOR, VERSION_PATCH};
 use milli::update::Settings as MilliSettings;
 use roaring::RoaringBitmap;
+use tempfile::PersistError;
 use time::OffsetDateTime;
 
 use super::create_batch::Batch;
 use crate::processing::{
     AtomicBatchStep, AtomicTaskStep, CreateIndexProgress, DeleteIndexProgress, FinalizingIndexStep,
-    InnerSwappingTwoIndexes, SwappingTheIndexes, TaskCancelationProgress, TaskDeletionProgress,
+    IndexCompaction, InnerSwappingTwoIndexes, SwappingTheIndexes, TaskCancelationProgress,
-    UpdateIndexProgress,
+    TaskDeletionProgress, UpdateIndexProgress,
 };
 use crate::utils::{
     self, remove_n_tasks_datetime_earlier_than, remove_task_datetime, swap_index_uid_in_task,
@@ -418,8 +422,45 @@ impl IndexScheduler {
                 task.status = Status::Succeeded;
                 Ok((vec![task], ProcessBatchInfo::default()))
             }
-            Batch::IndexCompaction { index_uid, mut task } => {
+            Batch::IndexCompaction { index_uid: _, mut task } => {
-                todo!("Implement index compaction")
+                let KindWithContent::IndexCompaction { index_uid } = &task.kind else {
+                    unreachable!()
+                };
+
+                let rtxn = self.env.read_txn()?;
+                let ret = catch_unwind(AssertUnwindSafe(|| {
+                    self.apply_compaction(&rtxn, &progress, index_uid)
+                }));
+
+                let (pre_size, post_size) = match ret {
+                    Ok(Ok(stats)) => stats,
+                    Ok(Err(Error::AbortedTask)) => return Err(Error::AbortedTask),
+                    Ok(Err(e)) => return Err(e),
+                    Err(e) => {
+                        let msg = match e.downcast_ref::<&'static str>() {
+                            Some(s) => *s,
+                            None => match e.downcast_ref::<String>() {
+                                Some(s) => &s[..],
+                                None => "Box<dyn Any>",
+                            },
+                        };
+                        return Err(Error::Export(Box::new(Error::ProcessBatchPanicked(
+                            msg.to_string(),
+                        ))));
+                    }
+                };
+
+                task.status = Status::Succeeded;
+                if let Some(Details::IndexCompaction {
+                    index_uid: _,
+                    pre_compaction_size,
+                    post_compaction_size,
+                }) = task.details.as_mut()
+                {
+                    *pre_compaction_size = Some(Byte::from_u64(pre_size));
+                    *post_compaction_size = Some(Byte::from_u64(post_size));
+                }
+                Ok((vec![task], ProcessBatchInfo::default()))
             }
             Batch::Export { mut task } => {
                 let KindWithContent::Export { url, api_key, payload_size, indexes } = &task.kind
@@ -496,6 +537,58 @@ impl IndexScheduler {
         }
     }
 
+    fn apply_compaction(
+        &self,
+        rtxn: &RoTxn,
+        progress: &Progress,
+        index_uid: &str,
+    ) -> Result<(u64, u64)> {
+        // 1. Verify that the index exists
+        if !self.index_mapper.index_exists(rtxn, index_uid)? {
+            return Err(Error::IndexNotFound(index_uid.to_owned()));
+        }
+
+        // 2. We retrieve the index and create a temporary file in the index directory
+        progress.update_progress(IndexCompaction::RetrieveTheIndex);
+        let index = self.index_mapper.index(rtxn, index_uid)?;
+        let pre_size = index.map_size() as u64;
+        progress.update_progress(IndexCompaction::CreateTemporaryFile);
+        let mut file = tempfile::Builder::new()
+            .suffix("data.")
+            .prefix(".mdb.cpy")
+            .tempfile_in(index.path())?;
+
+        // 3. We copy the index data to the temporary file
+        progress.update_progress(IndexCompaction::CopyAndCompactTheIndex);
+        index
+            .copy_to_file(file.as_file_mut(), CompactionOption::Enabled)
+            .map_err(|error| Error::Milli { error, index_uid: Some(index_uid.to_string()) })?;
+        // ...and reset the file position as specified in the documentation
+        file.seek(SeekFrom::Start(0))?;
+
+        // 4. We replace the index data file with the temporary file
+        progress.update_progress(IndexCompaction::PersistTheCompactedIndex);
+        let post_size = file.as_file().metadata()?.len();
+        match file.persist(index.path().join("data.mdb")) {
+            Ok(file) => file.sync_all()?,
+            // TODO see if we have a _resource busy_ error and probably handle this by:
+            //      1. closing the index, 2. replacing and 3. reopening it
+            Err(PersistError { error, file: _ }) => return Err(Error::IoError(error)),
+        };
+
+        // 5. prepare to close the index and wait for it
+        // The next time the index is opened, it will use the new compacted data
+        let closing_event = self.index_mapper.close_index(rtxn, index_uid)?;
+
+        if let Some(closing_event) = closing_event {
+            progress.update_progress(IndexCompaction::CloseTheIndex);
+            drop(index);
+            closing_event.wait();
+        }
+
+        Ok((pre_size, post_size))
+    }
+
     /// Swap the index `lhs` with the index `rhs`.
     fn apply_index_swap(
         &self,