jsancio commented on a change in pull request #10431:
URL: https://github.com/apache/kafka/pull/10431#discussion_r627658137
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File path: core/src/main/scala/kafka/raft/KafkaMetadataLog.scala
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@@ -242,85 +246,125 @@ final class KafkaMetadataLog private (
}
override def readSnapshot(snapshotId: OffsetAndEpoch):
Optional[RawSnapshotReader] = {
- try {
- if (snapshotIds.contains(snapshotId)) {
- Optional.of(FileRawSnapshotReader.open(log.dir.toPath, snapshotId))
- } else {
- Optional.empty()
+ snapshots synchronized {
+ val reader = snapshots.get(snapshotId) match {
+ case None =>
+ // Snapshot doesn't exists
+ None
+ case Some(None) =>
+ // Snapshot exists but has never been read before
+ try {
+ val snapshotReader =
Some(FileRawSnapshotReader.open(log.dir.toPath, snapshotId))
+ snapshots.put(snapshotId, snapshotReader)
+ snapshotReader
+ } catch {
+ case _: NoSuchFileException =>
+ // Snapshot doesn't exists in the data dir; remove
+ val path = Snapshots.snapshotPath(log.dir.toPath, snapshotId)
+ warn(s"Couldn't read $snapshotId; expected to find snapshot file
$path")
+ snapshots.remove(snapshotId)
+ None
+ }
+ case Some(value) =>
+ // Snapshot exists and it is already open; do nothing
+ value
}
- } catch {
- case _: NoSuchFileException =>
- Optional.empty()
+
+ reader.asJava.asInstanceOf[Optional[RawSnapshotReader]]
}
}
override def latestSnapshotId(): Optional[OffsetAndEpoch] = {
- val descending = snapshotIds.descendingIterator
- if (descending.hasNext) {
- Optional.of(descending.next)
- } else {
- Optional.empty()
+ snapshots synchronized {
Review comment:
Most modern hardware and Java's memory model require that values used by
multiple core/threads is read from RAM and written to RAM. In Java, you can
force this by using either using `volatile`, `synchronized` or a lot of the
types in the `java.util.concurrent` package. The important observation is that
this is needed for both reads and writes. This is a decent summary of the
issue:
https://medium.com/javarevisited/java-concurrency-java-memory-model-96e3ac36ec6b
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