[GitHub] [spark] HeartSaVioR commented on a change in pull request #31495: [SPARK-34383][SS] Optimize WAL commit phase on SS

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

HeartSaVioR commented on a change in pull request #31495:
URL: https://github.com/apache/spark/pull/31495#discussion_r571355810



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File path: sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/OffsetSeqLog.scala
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@@ -46,6 +47,23 @@ import org.apache.spark.sql.connector.read.streaming.{Offset => OffsetV2}
 class OffsetSeqLog(sparkSession: SparkSession, path: String)
   extends HDFSMetadataLog[OffsetSeq](sparkSession, path) {
 
+  private val cachedMetadata = new ju.TreeMap[Long, OffsetSeq]()
+
+  override def add(batchId: Long, metadata: OffsetSeq): Boolean = {
+    val added = super.add(batchId, metadata)
+    if (added) {
+      // cache metadata as it will be read again
+      cachedMetadata.put(batchId, metadata)
+      // we don't access metadata for (batchId - 2) batches; evict them

Review comment:
       Note for reviewers: see MicroBatchExecution / ContinuousExecution around calling `source.commit()`. To provide the offset metadata to source side we read offset metadata for previous batch, which is probably written by this driver in previous batches.




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