[Spark][Version Checksum] Incrementally compute VersionChecksum setTr…

…ansactions and domainMetadata (#3895)

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#### Which Delta project/connector is this regarding?
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- [X] Spark
- [ ] Standalone
- [ ] Flink
- [ ] Kernel
- [ ] Other (fill in here)

## Description

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Follow up for #3828. Adds support
for incrementally computing the set transactions and domain metadata
actions based on the current commit and the last version checksum.
Incremental computation for both these action types have thresholds so
that we don't store them if they are too long (tests have been added for
the same).


## How was this patch tested?

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Added new tests in DomainMetadataSuite and a new suite called
`DeltaIncrementalSetTransactionsSuite`

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

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No

spark/src/main/scala/org/apache/spark/sql/delta/Checksum.scala

@@ -78,9 +78,7 @@ trait RecordChecksum extends DeltaLogging {
   private lazy val writer =
     CheckpointFileManager.create(deltaLog.logPath, deltaLog.newDeltaHadoopConf())
 
-  private def getChecksum(snapshot: Snapshot): VersionChecksum = {
-    snapshot.checksumOpt.getOrElse(snapshot.computeChecksum)
-  }
+  private def getChecksum(snapshot: Snapshot): VersionChecksum = snapshot.computeChecksum
 
   protected def writeChecksumFile(txnId: String, snapshot: Snapshot): Unit = {
     if (!spark.sessionState.conf.getConf(DeltaSQLConf.DELTA_WRITE_CHECKSUM_ENABLED)) {
@@ -277,6 +275,12 @@ trait RecordChecksum extends DeltaLogging {
       case _ =>
     }
 
+    val setTransactions = incrementallyComputeSetTransactions(
+      oldSnapshot, oldVersionChecksum, attemptVersion, actions)
+
+    val domainMetadata = incrementallyComputeDomainMetadatas(
+      oldSnapshot, oldVersionChecksum, attemptVersion, actions)
+
     Right(VersionChecksum(
       txnId = txnIdOpt,
       tableSizeBytes = tableSizeBytes,
@@ -286,13 +290,106 @@ trait RecordChecksum extends DeltaLogging {
       inCommitTimestampOpt = inCommitTimestamp,
       metadata = metadata,
       protocol = protocol,
-      setTransactions = None,
-      domainMetadata = None,
+      setTransactions = setTransactions,
+      domainMetadata = domainMetadata,
       histogramOpt = None,
       allFiles = None
     ))
   }
 
+  /**
+   * Incrementally compute [[Snapshot.setTransactions]] for the commit `attemptVersion`.
+   *
+   * @param oldSnapshot - snapshot corresponding to `attemptVersion` - 1
+   * @param oldVersionChecksum - [[VersionChecksum]] corresponding to `attemptVersion` - 1
+   * @param attemptVersion - version which we want to commit
+   * @param actionsToCommit - actions for commit `attemptVersion`
+   * @return Optional sequence of incrementally computed [[SetTransaction]]s for commit
+   *         `attemptVersion`.
+   */
+  private def incrementallyComputeSetTransactions(
+      oldSnapshot: Option[Snapshot],
+      oldVersionChecksum: VersionChecksum,
+      attemptVersion: Long,
+      actionsToCommit: Seq[Action]): Option[Seq[SetTransaction]] = {
+    // Check-1: check conf
+    if (!spark.conf.get(DeltaSQLConf.DELTA_WRITE_SET_TRANSACTIONS_IN_CRC)) {
+      return None
+    }
+
+    // Check-2: check `minSetTransactionRetentionTimestamp` is not set
+    val newMetadataToCommit = actionsToCommit.collectFirst { case m: Metadata => m }
+    // TODO: Add support for incrementally computing [[SetTransaction]]s even when
+    //  `minSetTransactionRetentionTimestamp` is set.
+    // We don't incrementally compute [[SetTransaction]]s when user has configured
+    // `minSetTransactionRetentionTimestamp` as it makes verification non-deterministic.
+    // Check all places to figure out whether `minSetTransactionRetentionTimestamp` is set:
+    // 1. oldSnapshot corresponding to `attemptVersion - 1`
+    // 2. old VersionChecksum's MetaData (corresponding to `attemptVersion-1`)
+    // 3. new VersionChecksum's MetaData (corresponding to `attemptVersion`)
+    val setTransactionRetentionTimestampConfigured =
+      (oldSnapshot.map(_.metadata) ++ Option(oldVersionChecksum.metadata) ++ newMetadataToCommit)
+        .exists(DeltaLog.minSetTransactionRetentionInterval(_).nonEmpty)
+    if (setTransactionRetentionTimestampConfigured) return None
+
+    // Check-3: Check old setTransactions are available so that we can incrementally compute new.
+    val oldSetTransactions = oldVersionChecksum.setTransactions
+      .getOrElse { return None }
+
+    // Check-4: old/new setTransactions are within the threshold.
+    val setTransactionsToCommit = actionsToCommit.filter(_.isInstanceOf[SetTransaction])
+    val threshold = spark.sessionState.conf.getConf(DeltaSQLConf.DELTA_MAX_SET_TRANSACTIONS_IN_CRC)
+    if (Math.max(setTransactionsToCommit.size, oldSetTransactions.size) > threshold) return None
+
+    // We currently don't attempt incremental [[SetTransaction]] when
+    // `minSetTransactionRetentionTimestamp` is set. So passing this as None here explicitly.
+    // We can also ignore file retention because that only affects [[RemoveFile]] actions.
+    val logReplay = new InMemoryLogReplay(
+      minFileRetentionTimestamp = 0,
+      minSetTransactionRetentionTimestamp = None)
+
+    logReplay.append(attemptVersion - 1, oldSetTransactions.toIterator)
+    logReplay.append(attemptVersion, setTransactionsToCommit.toIterator)
+    Some(logReplay.getTransactions.toSeq).filter(_.size <= threshold)
+  }
+
+  /**
+   * Incrementally compute [[Snapshot.domainMetadata]] for the commit `attemptVersion`.
+   *
+   * @param oldVersionChecksum - [[VersionChecksum]] corresponding to `attemptVersion` - 1
+   * @param attemptVersion - version which we want to commit
+   * @param actionsToCommit - actions for commit `attemptVersion`
+   * @return Sequence of incrementally computed [[DomainMetadata]]s for commit
+   *         `attemptVersion`.
+   */
+  private def incrementallyComputeDomainMetadatas(
+      oldSnapshot: Option[Snapshot],
+      oldVersionChecksum: VersionChecksum,
+      attemptVersion: Long,
+      actionsToCommit: Seq[Action]): Option[Seq[DomainMetadata]] = {
+    // Check old DomainMetadatas are available so that we can incrementally compute new.
+    val oldDomainMetadatas = oldVersionChecksum.domainMetadata
+      .getOrElse { return None }
+    val newDomainMetadatas = actionsToCommit.filter(_.isInstanceOf[DomainMetadata])
+
+    // We only work with DomainMetadata, so RemoveFile and SetTransaction retention don't matter.
+    val logReplay = new InMemoryLogReplay(
+      minFileRetentionTimestamp = 0,
+      minSetTransactionRetentionTimestamp = None)
+
+    val threshold = spark.sessionState.conf.getConf(DeltaSQLConf.DELTA_MAX_DOMAIN_METADATAS_IN_CRC)
+
+    logReplay.append(attemptVersion - 1, oldDomainMetadatas.iterator)
+    logReplay.append(attemptVersion, newDomainMetadatas.iterator)
+    // We don't truncate the set of DomainMetadata actions. Instead, we either store all of them or
+    // none of them. The advantage of this is that you can then determine presence based on the
+    // checksum, i.e. if the checksum contains domain metadatas but it doesn't contain the one you
+    // are looking for, then it's not there.
+    //
+    // It's also worth noting that we can distinguish "no domain metadatas" versus
+    // "domain metadatas not stored" as [[Some]] vs. [[None]].
+    Some(logReplay.getDomainMetadatas.toSeq).filter(_.size <= threshold)
+  }
 }
 
 object RecordChecksum {

spark/src/main/scala/org/apache/spark/sql/delta/Snapshot.scala

@@ -513,17 +513,29 @@ class Snapshot(
    */
   def computeChecksum: VersionChecksum = VersionChecksum(
     txnId = None,
-    tableSizeBytes = sizeInBytes,
-    numFiles = numOfFiles,
-    numMetadata = numOfMetadata,
-    numProtocol = numOfProtocol,
     inCommitTimestampOpt = getInCommitTimestampOpt,
-    setTransactions = checksumOpt.flatMap(_.setTransactions),
-    domainMetadata = checksumOpt.flatMap(_.domainMetadata),
     metadata = metadata,
     protocol = protocol,
-    histogramOpt = checksumOpt.flatMap(_.histogramOpt),
-    allFiles = checksumOpt.flatMap(_.allFiles))
+    allFiles = checksumOpt.flatMap(_.allFiles),
+    tableSizeBytes = checksumOpt.map(_.tableSizeBytes).getOrElse(sizeInBytes),
+    numFiles = checksumOpt.map(_.numFiles).getOrElse(numOfFiles),
+    numMetadata = checksumOpt.map(_.numMetadata).getOrElse(numOfMetadata),
+    numProtocol = checksumOpt.map(_.numProtocol).getOrElse(numOfProtocol),
+    // Only return setTransactions and domainMetadata if they are either already present
+    // in the checksum or if they have already been computed in the current snapshot.
+    setTransactions = checksumOpt.flatMap(_.setTransactions)
+      .orElse {
+        Option.when(_computedStateTriggered &&
+            // Only extract it from the current snapshot if set transaction
+            // writes are enabled.
+            spark.conf.get(DeltaSQLConf.DELTA_WRITE_SET_TRANSACTIONS_IN_CRC)) {
+          setTransactions
+        }
+      },
+    domainMetadata = checksumOpt.flatMap(_.domainMetadata)
+      .orElse(Option.when(_computedStateTriggered)(domainMetadata)),
+    histogramOpt = checksumOpt.flatMap(_.histogramOpt)
+  )
 
   /** Returns the data schema of the table, used for reading stats */
   def tableSchema: StructType = metadata.dataSchema
@@ -704,6 +716,7 @@ class DummySnapshot(
 
   override protected lazy val computedState: SnapshotState = initialState(metadata, protocol)
   override protected lazy val getInCommitTimestampOpt: Option[Long] = None
+  _computedStateTriggered = true
 
   // The [[InitialSnapshot]] is not backed by any external commit-coordinator.
   override val tableCommitCoordinatorClientOpt: Option[TableCommitCoordinatorClient] = None

spark/src/main/scala/org/apache/spark/sql/delta/SnapshotManagement.scala

@@ -1271,6 +1271,7 @@ trait SnapshotManagement { self: DeltaLog =>
         // a checksum based on state reconstruction. Disable incremental commit to avoid
         // further error triggers in this session.
         spark.sessionState.conf.setConf(DeltaSQLConf.INCREMENTAL_COMMIT_ENABLED, false)
+        spark.sessionState.conf.setConf(DeltaSQLConf.DELTA_WRITE_SET_TRANSACTIONS_IN_CRC, false)
         return createSnapshotAfterCommit(
           initSegment,
           newChecksumOpt = None,

spark/src/main/scala/org/apache/spark/sql/delta/SnapshotState.scala

@@ -65,6 +65,9 @@ trait SnapshotStateManager extends DeltaLogging { self: Snapshot =>
 
   // For implicits which re-use Encoder:
   import implicits._
+  /** Whether computedState is already computed or not */
+  @volatile protected var _computedStateTriggered: Boolean = false
+
 
   /** A map to look up transaction version by appId. */
   lazy val transactions: Map[String, Long] = setTransactions.map(t => t.appId -> t.version).toMap
@@ -114,6 +117,7 @@ trait SnapshotStateManager extends DeltaLogging { self: Snapshot =>
           throw DeltaErrors.actionNotFoundException("metadata", version)
         }
 
+        _computedStateTriggered = true
         _computedState
       }
     }

spark/src/main/scala/org/apache/spark/sql/delta/sources/DeltaSQLConf.scala

@@ -1073,6 +1073,31 @@ trait DeltaSQLConfBase {
       .booleanConf
       .createWithDefault(true)
 
+  val DELTA_WRITE_SET_TRANSACTIONS_IN_CRC =
+    buildConf("setTransactionsInCrc.writeOnCommit")
+      .internal()
+      .doc("When enabled, each commit will incrementally compute and cache all SetTransaction" +
+        " actions in the .crc file. Note that this only happens when incremental commits" +
+        s" are enabled (${INCREMENTAL_COMMIT_ENABLED.key})")
+      .booleanConf
+      .createWithDefault(true)
+
+  val DELTA_MAX_SET_TRANSACTIONS_IN_CRC =
+    buildConf("setTransactionsInCrc.maxAllowed")
+      .internal()
+      .doc("Threshold of the number of SetTransaction actions below which this optimization" +
+        " should be enabled")
+      .longConf
+      .createWithDefault(100)
+
+  val DELTA_MAX_DOMAIN_METADATAS_IN_CRC =
+    buildConf("domainMetadatasInCrc.maxAllowed")
+      .internal()
+      .doc("Threshold of the number of DomainMetadata actions below which this optimization" +
+        " should be enabled")
+      .longConf
+      .createWithDefault(10)
+
   val DELTA_CHECKPOINT_THROW_EXCEPTION_WHEN_FAILED =
       buildConf("checkpoint.exceptionThrowing.enabled")
         .internal()