feat: Improve shuffle metrics (second attempt)

docs/source/index.rst

@@ -51,6 +51,7 @@ as a native runtime to achieve improvement in terms of query efficiency and quer
    Configuration Settings <user-guide/configs>
    Compatibility Guide <user-guide/compatibility>
    Tuning Guide <user-guide/tuning>
+   Metrics Guide <user-guide/metrics>
 
 .. _toc.contributor-guide-links:
 .. toctree::

docs/source/user-guide/metrics.md

@@ -0,0 +1,66 @@
+<!---
+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.
+-->
+
+# Comet Metrics
+
+## Spark SQL Metrics
+
+Set `spark.comet.metrics.detailed=true` to see all available Comet metrics.
+
+### CometScanExec
+
+| Metric      | Description                                                                                                                                                                                                                                                                        |
+| ----------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `scan time` | Total time to scan a Parquet file. This is not comparable to the same metric in Spark because Comet's scan metric is more accurate. Although both Comet and Spark measure the time in nanoseconds, Spark rounds this time to the nearest millisecond per batch and Comet does not. |
+
+### Exchange
+
+Comet adds some additional metrics:
+
+| Metric                          | Description                                                   |
+| ------------------------------- | ------------------------------------------------------------- |
+| `native shuffle time`           | Total time in native code excluding any child operators.      |
+| `repartition time`              | Time to repartition batches.                                  |
+| `memory pool time`              | Time interacting with memory pool.                            |
+| `encoding and compression time` | Time to encode batches in IPC format and compress using ZSTD. |
+
+## Native Metrics
+
+Setting `spark.comet.explain.native.enabled=true` will cause native plans to be logged in each executor. Metrics are
+logged for each native plan (and there is one plan per task, so this is very verbose).
+
+Here is a guide to some of the native metrics.
+
+### ScanExec
+
+| Metric            | Description                                                                                         |
+| ----------------- | --------------------------------------------------------------------------------------------------- |
+| `elapsed_compute` | Total time spent in this operator, fetching batches from a JVM iterator.                            |
+| `jvm_fetch_time`  | Time spent in the JVM fetching input batches to be read by this `ScanExec` instance.                |
+| `arrow_ffi_time`  | Time spent using Arrow FFI to create Arrow batches from the memory addresses returned from the JVM. |
+
+### ShuffleWriterExec
+
+| Metric            | Description                                                   |
+| ----------------- | ------------------------------------------------------------- |
+| `elapsed_compute` | Total time excluding any child operators.                     |
+| `repart_time`     | Time to repartition batches.                                  |
+| `ipc_time`        | Time to encode batches in IPC format and compress using ZSTD. |
+| `mempool_time`    | Time interacting with memory pool.                            |
+| `write_time`      | Time spent writing bytes to disk.                             |

docs/source/user-guide/tuning.md

@@ -103,31 +103,6 @@ native shuffle currently only supports `HashPartitioning` and `SinglePartitionin
 To enable native shuffle, set `spark.comet.exec.shuffle.mode` to `native`. If this mode is explicitly set,
 then any shuffle operations that cannot be supported in this mode will fall back to Spark.
 
-##  Metrics
-
-### Spark SQL Metrics
-
-Some Comet metrics are not directly comparable to Spark metrics in some cases:
-
-- `CometScanExec` uses nanoseconds for total scan time. Spark also measures scan time in nanoseconds but converts to
-  milliseconds _per batch_ which can result in a large loss of precision, making it difficult to compare scan times
-  between Spark and Comet.
-
-### Native Metrics
-
-Setting `spark.comet.explain.native.enabled=true` will cause native plans to be logged in each executor. Metrics are
-logged for each native plan (and there is one plan per task, so this is very verbose).
-
-Here is a guide to some of the native metrics.
-
-### ScanExec
-
-| Metric            | Description                                                                                         |
-| ----------------- | --------------------------------------------------------------------------------------------------- |
-| `elapsed_compute` | Total time spent in this operator, fetching batches from a JVM iterator.                            |
-| `jvm_fetch_time`  | Time spent in the JVM fetching input batches to be read by this `ScanExec` instance.                |
-| `arrow_ffi_time`  | Time spent using Arrow FFI to create Arrow batches from the memory addresses returned from the JVM. |
-
 ## Explain Plan
 ### Extended Explain
 With Spark 4.0.0 and newer, Comet can provide extended explain plan information in the Spark UI. Currently this lists

native/core/src/execution/shuffle/row.rs

@@ -40,6 +40,7 @@ use arrow_array::{
     Array, ArrayRef, RecordBatch, RecordBatchOptions,
 };
 use arrow_schema::{ArrowError, DataType, Field, Schema, TimeUnit};
+use datafusion::physical_plan::metrics::Time;
 use jni::sys::{jint, jlong};
 use std::{
     fs::OpenOptions,
@@ -3354,7 +3355,10 @@ pub fn process_sorted_row_partition(
         let mut frozen: Vec<u8> = vec![];
         let mut cursor = Cursor::new(&mut frozen);
         cursor.seek(SeekFrom::End(0))?;
-        written += write_ipc_compressed(&batch, &mut cursor)?;
+
+        // we do not collect metrics in Native_writeSortedFileNative
+        let ipc_time = Time::default();
+        written += write_ipc_compressed(&batch, &mut cursor, &ipc_time)?;
 
         if let Some(checksum) = &mut current_checksum {
             checksum.update(&mut cursor)?;