[GitHub] [arrow-datafusion] yjshen commented on a change in pull request #1526: A simplified memory manager for query execution

[GitBox <gi...@apache.org>]

yjshen commented on a change in pull request #1526:
URL: https://github.com/apache/arrow-datafusion/pull/1526#discussion_r780631979



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File path: datafusion/src/execution/memory_manager.rs
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@@ -0,0 +1,320 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Manages all available memory during query execution
+
+use crate::error::Result;
+use async_trait::async_trait;
+use hashbrown::HashMap;
+use log::info;
+use std::fmt;
+use std::fmt::{Debug, Display, Formatter};
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::{Arc, Mutex};
+use std::time::Duration;
+use tokio::task;
+use tokio::task::JoinHandle;
+
+static mut CONSUMER_ID: AtomicUsize = AtomicUsize::new(0);
+
+fn next_id() -> usize {
+    unsafe { CONSUMER_ID.fetch_add(1, Ordering::SeqCst) }
+}
+
+/// Type of the memory consumer
+pub enum ConsumerType {
+    /// consumers that can grow or shrink its memory usage during execution
+    /// such as spillable sorter, spillable hashmap, etc.
+    Controlling,
+    /// consumers that are not spillable, counting in for only tracking purpose.
+    Tracking,
+}
+
+#[derive(Clone, Debug, Hash, Eq, PartialEq)]
+/// Id that uniquely identifies a Memory Consumer
+pub struct MemoryConsumerId {
+    /// partition the consumer belongs to
+    pub partition_id: usize,
+    /// unique id
+    pub id: usize,
+}
+
+impl MemoryConsumerId {
+    /// Auto incremented new Id
+    pub fn new(partition_id: usize) -> Self {
+        let id = next_id();
+        Self { partition_id, id }
+    }
+}
+
+impl Display for MemoryConsumerId {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "{}:{}", self.partition_id, self.id)
+    }
+}
+
+#[async_trait]
+/// A memory consumer that either takes up memory (of type `ConsumerType::Tracking`)
+/// or grows/shrinks memory usage based on available memory (of type `ConsumerType::Controlling`).
+pub trait MemoryConsumer: Send + Sync + Debug {
+    /// Display name of the consumer
+    fn name(&self) -> String;
+
+    /// Unique id of the consumer
+    fn id(&self) -> &MemoryConsumerId;
+
+    /// Ptr to MemoryManager
+    fn memory_manager(&self) -> Arc<MemoryManager>;
+
+    /// Partition that the consumer belongs to
+    fn partition_id(&self) -> usize {
+        self.id().partition_id
+    }
+
+    /// Type of the consumer
+    fn type_(&self) -> &ConsumerType;
+
+    /// Grow memory by `required` to buffer more data in memory,
+    /// this may trigger spill before grow when the memory threshold is
+    /// reached for this consumer.
+    async fn try_grow(&self, required: usize) -> Result<()> {
+        let current_usage = self.mem_used();
+        let can_grow = self
+            .memory_manager()
+            .try_grow(required, current_usage, self.id())
+            .await;
+        if !can_grow {
+            info!(
+                "Failed to grow memory of {} from {}, spilling...",
+                human_readable_size(required),
+                self.id()
+            );
+            self.spill().await?;
+        }
+        Ok(())
+    }
+
+    /// Spill in-memory buffers to disk, free memory
+    async fn spill(&self) -> Result<()>;
+
+    /// Current memory used by this consumer
+    fn mem_used(&self) -> usize;
+
+    /// Current status of the consumer
+    fn str_repr(&self) -> String {
+        let mem = self.mem_used();
+        format!(
+            "{}[{}]: {}",
+            self.name(),
+            self.id(),
+            human_readable_size(mem)
+        )
+    }
+}
+
+/*
+The memory management architecture is the following:
+
+1. User designates max execution memory by setting RuntimeConfig.max_memory and RuntimeConfig.memory_fraction (float64 between 0..1).
+   The actual max memory DataFusion could use `pool_size =  max_memory * memory_fraction`.
+2. The entities that take up memory during its execution are called 'Memory Consumers'. Operators or others are encouraged to
+   register themselves to the memory manager and report its usage through `mem_used()`.
+3. There are two kinds of consumers:
+   - 'Controlling' consumers that would acquire memory during its execution and release memory through `spill` if no more memory is available.
+   - 'Tracking' consumers that exist for reporting purposes to provide a more accurate memory usage estimation for memory consumers.
+4. Controlling and tracking consumers share the pool. Each controlling consumer could acquire a maximum of
+   (pool_size - all_tracking_used) / active_num_controlling_consumers.
+
+            Memory Space for the DataFusion Lib / Process of `pool_size`
+   ┌──────────────────────────────────────────────z─────────────────────────────┐
+   │                                              z                             │
+   │                                              z                             │
+   │               Controlling                    z          Tracking           │
+   │            Memory Consumers                  z       Memory Consumers      │
+   │                                              z                             │
+   │                                              z                             │
+   └──────────────────────────────────────────────z─────────────────────────────┘
+*/
+
+/// Manage memory usage during physical plan execution
+pub struct MemoryManager {
+    consumers: Arc<Mutex<HashMap<MemoryConsumerId, Arc<dyn MemoryConsumer>>>>,
+    trackers: Arc<Mutex<HashMap<MemoryConsumerId, Arc<dyn MemoryConsumer>>>>,
+    trackers_total_usage: AtomicUsize,
+    pool_size: usize,
+    join_handle: Arc<Mutex<Option<JoinHandle<()>>>>,
+}
+
+impl MemoryManager {
+    /// Create new memory manager based on max available pool_size
+    pub fn new(pool_size: usize) -> Self {
+        info!(
+            "Creating memory manager with initial size {}",
+            human_readable_size(pool_size)
+        );
+        Self {
+            consumers: Arc::new(Mutex::new(HashMap::new())),
+            trackers: Arc::new(Mutex::new(HashMap::new())),
+            trackers_total_usage: AtomicUsize::new(0),
+            pool_size,
+            join_handle: Arc::new(Mutex::new(None)),
+        }
+    }
+
+    fn update_tracker_total(self: &Arc<Self>) {
+        let trackers = self.trackers.lock().unwrap();
+        if trackers.len() > 0 {
+            let sum = trackers.values().fold(0usize, |acc, y| acc + y.mem_used());
+            drop(trackers);
+            self.trackers_total_usage.store(sum, Ordering::SeqCst);
+        }
+    }
+
+    /// Initialize
+    pub(crate) fn initialize(self: &Arc<Self>) {
+        let manager = self.clone();
+        let handle = task::spawn(async move {

Review comment:
       Yes, I'm creating a background task that runs periodically to update `tracking consumers'` total memory usage, to avoid `controlling consumers` to ask for available memory frequently.




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