Ngone51 commented on a change in pull request #31495:
URL: https://github.com/apache/spark/pull/31495#discussion_r571434537
##########
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:
`TreeMap` seems overkill to me if we only cache at most 2 batches. How
about using a 2-size array? We can put/get the elements by the index of
(batchId % 2).
For example:
```scala
private val cachedMetadata = Array[OffsetSeq](null, null)
// put
cachedMetadata(batchId % 2) = metadata
// get
Option(cachedMetadata(batchId % 2)).orElse(super.get(batchId))
```
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