[SPARK] Emit event for CDF calls. (delta-io#4883)

<!--
Thanks for sending a pull request!  Here are some tips for you:
1. If this is your first time, please read our contributor guidelines:
https://github.com/delta-io/delta/blob/master/CONTRIBUTING.md
2. If the PR is unfinished, add '[WIP]' in your PR title, e.g., '[WIP]
Your PR title ...'.
  3. Be sure to keep the PR description updated to reflect all changes.
  4. Please write your PR title to summarize what this PR proposes.
5. If possible, provide a concise example to reproduce the issue for a
faster review.
6. If applicable, include the corresponding issue number in the PR title
and link it in the body.
-->

#### Which Delta project/connector is this regarding?
<!--
Please add the component selected below to the beginning of the pull
request title
For example: [Spark] Title of my pull request
-->

- [x] Spark
- [ ] Standalone
- [ ] Flink
- [ ] Kernel
- [ ] Other (fill in here)

## Description
Add a new log event for cdf execution.

<!--
- Describe what this PR changes.
- Describe why we need the change.
 
If this PR resolves an issue be sure to include "Resolves #XXX" to
correctly link and close the issue upon merge.
-->

## How was this patch tested?
UT
<!--
If tests were added, say they were added here. Please make sure to test
the changes thoroughly including negative and positive cases if
possible.
If the changes were tested in any way other than unit tests, please
clarify how you tested step by step (ideally copy and paste-able, so
that other reviewers can test and check, and descendants can verify in
the future).
If the changes were not tested, please explain why.
-->

## Does this PR introduce _any_ user-facing changes?

<!--
If yes, please clarify the previous behavior and the change this PR
proposes - provide the console output, description and/or an example to
show the behavior difference if possible.
If possible, please also clarify if this is a user-facing change
compared to the released Delta Lake versions or within the unreleased
branches such as master.
If no, write 'No'.
-->

---------

Co-authored-by: Omar Elhadidy <[email protected]>

Author: Omar-Saleh

spark/src/main/scala/org/apache/spark/sql/delta/commands/cdc/CDCReader.scala

@@ -616,7 +616,7 @@ trait CDCReaderImpl extends DeltaLogging {
     }
 
     var totalBytes = 0L
-    var totalFiles = 0L
+    var numAddFiles, numRemoveFiles, numAddCRCFiles = 0L
 
     changes.foreach {
       case (v, actions) =>
@@ -659,13 +659,13 @@ trait CDCReaderImpl extends DeltaLogging {
         actions.foreach {
           case c: AddCDCFile =>
             cdcActions.append(c)
-            totalFiles += 1L
+            numAddCRCFiles += 1L
             totalBytes += c.size
           case a: AddFile =>
-            totalFiles += 1L
+            numAddFiles += 1L
             totalBytes += a.size
           case r: RemoveFile =>
-            totalFiles += 1L
+            numRemoveFiles += 1L
             totalBytes += r.size.getOrElse(0L)
           case i: CommitInfo => commitInfo = Some(i)
           case _ => // do nothing
@@ -753,6 +753,21 @@ trait CDCReaderImpl extends DeltaLogging {
     val emptyDf =
       DataFrameUtils.ofRows(spark.sqlContext.sparkSession, emptyRdd)
 
+    recordDeltaEvent(
+      deltaLog,
+      "delta.changeDataFeed.changesToDF",
+      data = Map(
+        "startVersion" -> start,
+        "endVersion" -> end,
+        "useCoarseGrainedCDC" -> useCoarseGrainedCDC,
+        "numAddFiles" -> numAddFiles,
+        "numRemoveFiles" -> numRemoveFiles,
+        "numAddCRCFiles" -> numAddCRCFiles,
+        "totalBytes" -> totalBytes,
+        "isStreaming" -> isStreaming
+      )
+    )
+    val totalFiles = numAddFiles + numRemoveFiles + numAddCRCFiles
     CDCVersionDiffInfo(
       (emptyDf +: dfs).reduce((df1, df2) => df1.union(
         df2

spark/src/test/scala/org/apache/spark/sql/delta/cdc/CDCReaderSuite.scala

@@ -19,6 +19,7 @@ package org.apache.spark.sql.delta.cdc
 // scalastyle:off import.ordering.noEmptyLine
 import java.io.File
 
+import com.databricks.spark.util.Log4jUsageLogger
 import org.apache.spark.sql.delta._
 import org.apache.spark.sql.delta.DeltaOperations.Delete
 import org.apache.spark.sql.delta.DeltaTestUtils.BOOLEAN_DOMAIN
@@ -449,5 +450,21 @@ class CDCReaderSuite
       }
     }
   }
+
+  test("Logs are generated for changesToDF") {
+    withTempDir { dir =>
+      val events = Log4jUsageLogger.track {
+        val log = DeltaLog.forTable(spark, dir.getAbsolutePath)
+        val data = spark.range(10)
+
+        data.write.format("delta").save(dir.getAbsolutePath)
+        sql(s"DELETE FROM delta.`${dir.getAbsolutePath}`")
+        CDCReader.changesToBatchDF(log, 0, 1, spark)
+      }
+
+      assert(events.exists(event => event.metric == "tahoeEvent" &&
+        event.tags.get("opType") == Option("delta.changeDataFeed.changesToDF")))
+    }
+  }
 }