Batch up pointer writes to reduce sync() bottleneck in SQLite

yama/src/pile/local_sqlitebloblogs.rs

@@ -39,6 +39,9 @@ use rusqlite::ffi::ErrorCode::ConstraintViolation;
 /// Bloblogs will not be reused if they are already 2 GiB large.
 pub const MAX_BLOBLOG_REUSE_SIZE: u64 = 2 * 1024 * 1024 * 1024;
 
+/// This many pointers will be batched up for writing.
+pub const POINTER_WRITE_BATCHES: usize = 2048;
+
 /// A file storing a log of blobs.
 /// Format:
 ///     Repeated:
@@ -130,6 +133,54 @@ pub struct Inner {
     open_bloblogs: HashMap<BloblogId, Arc<Mutex<Bloblog>>>, // TODO want an LRU cache with a weak hashmap...?
     connection: Connection,
     writers_in_progress: u16,
+    // We batch up pointer writes because sync() performance really hurts us if we do them one by
+    // one.
+    queued_pointer_writes: HashMap<ChunkId, BloblogPointer>,
+}
+
+impl Inner {
+    pub fn raw_put_chunk_pointer(
+        &self,
+        chunk_id: &ChunkId,
+        bloblog: BloblogId,
+        offset_i64: i64,
+    ) -> anyhow::Result<()> {
+        match self.connection.execute(
+            "INSERT INTO chunks (chunk_id, bloblog, offset) VALUES (?1, ?2, ?3)",
+            params![&chunk_id[..], bloblog, offset_i64],
+        ) {
+            Ok(_) => Ok(()),
+            Err(Error::SqliteFailure(e, str)) => {
+                if e.code == ConstraintViolation {
+                    warn!(
+                        "(ignoring) SQLite constraint violation on insertion... {:?}",
+                        str
+                    );
+                    Ok(())
+                } else {
+                    Err(Error::SqliteFailure(e, str))?;
+                    unreachable!();
+                }
+            }
+            other => {
+                other?;
+                unreachable!();
+            }
+        }
+    }
+
+    pub fn flush(&mut self) -> anyhow::Result<()> {
+        // Create a non-allocated hashmap to satisfy borrow checker, then swap it in and out
+        let mut queued_pointer_writes = HashMap::with_capacity(0);
+        std::mem::swap(&mut self.queued_pointer_writes, &mut queued_pointer_writes);
+        for (chunk_id, pointer) in queued_pointer_writes.drain() {
+            let offset_i64 =
+                i64::try_from(pointer.offset).expect("ouch! can't turn u64 into i64...");
+            self.raw_put_chunk_pointer(&chunk_id, pointer.bloblog, offset_i64)?;
+        }
+        std::mem::swap(&mut self.queued_pointer_writes, &mut queued_pointer_writes);
+        Ok(())
+    }
 }
 
 /// A Pile built on the idea of SQLite-indexed 'blob logs'.
@@ -144,6 +195,7 @@ pub struct SqliteBloblogPile {
     inner: Arc<Mutex<Inner>>,
     path: PathBuf,
     writers_reach_zero: Condvar,
+    should_batch_pointer_writes: bool,
 }
 
 /// A pointer to a blob in a 'blob log'.
@@ -193,9 +245,11 @@ impl SqliteBloblogPile {
                 open_bloblogs: HashMap::new(),
                 connection,
                 writers_in_progress: 0,
+                queued_pointer_writes: Default::default(),
             })),
             path: path.to_owned(),
             writers_reach_zero: Default::default(),
+            should_batch_pointer_writes: true,
         })
     }
 
@@ -287,28 +341,34 @@ impl SqliteBloblogPile {
     fn put_chunk_pointer(&self, chunk_id: &ChunkId, pointer: BloblogPointer) -> anyhow::Result<()> {
         let inner = self.inner.lock().unwrap();
         let offset_i64 = i64::try_from(pointer.offset).expect("ouch! can't turn u64 into i64...");
-        match inner.connection.execute(
-            "INSERT INTO chunks (chunk_id, bloblog, offset) VALUES (?1, ?2, ?3)",
-            params![&chunk_id[..], pointer.bloblog, offset_i64],
-        ) {
-            Ok(_) => Ok(()),
-            Err(Error::SqliteFailure(e, str)) => {
-                if e.code == ConstraintViolation {
-                    warn!(
-                        "(ignoring) SQLite constraint violation on insertion... {:?}",
-                        str
-                    );
-                    Ok(())
-                } else {
-                    Err(Error::SqliteFailure(e, str))?;
-                    unreachable!();
-                }
-            }
-            other => {
-                other?;
-                unreachable!();
-            }
+        inner.raw_put_chunk_pointer(chunk_id, pointer.bloblog, offset_i64)
+    }
+
+    fn batched_put_chunk_pointer(
+        &self,
+        chunk_id: &ChunkId,
+        pointer: BloblogPointer,
+    ) -> anyhow::Result<()> {
+        let mut inner = self.inner.lock().unwrap();
+        inner
+            .queued_pointer_writes
+            .insert(chunk_id.clone(), pointer);
+        if inner.queued_pointer_writes.len() >= POINTER_WRITE_BATCHES {
+            inner.flush()?;
         }
+        Ok(())
+    }
+
+    fn flush_queued_pointer_writes(&self) -> anyhow::Result<()> {
+        let mut inner = self.inner.lock().unwrap();
+        inner.flush()
+    }
+}
+
+impl Drop for SqliteBloblogPile {
+    fn drop(&mut self) {
+        self.flush_queued_pointer_writes()
+            .expect("POSSIBILITY OF LOSS OF NEW DATA: failed to flush queued pointer writes!");
     }
 }
 
@@ -385,7 +445,11 @@ impl RawPile for SqliteBloblogPile {
                     offset,
                 };
 
-                self.put_chunk_pointer(&chunk_id, pointer)?;
+                if self.should_batch_pointer_writes {
+                    self.batched_put_chunk_pointer(&chunk_id, pointer)?;
+                } else {
+                    self.put_chunk_pointer(&chunk_id, pointer)?;
+                }
                 Ok(())
             }
             Keyspace::ChunkHash => unimplemented!(),