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https://issues.apache.org/jira/browse/HADOOP-18184?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17746629#comment-17746629
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ASF GitHub Bot commented on HADOOP-18184:
-----------------------------------------
steveloughran commented on code in PR #5832:
URL: https://github.com/apache/hadoop/pull/5832#discussion_r1272698192
##########
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/impl/prefetch/CachingBlockManager.java:
##########
@@ -298,16 +306,26 @@ public void requestPrefetch(int blockNumber) {
/**
* Requests cancellation of any previously issued prefetch requests.
+ * If the reason was switching to random IO, any active prefetched blocks
+ * are still cached.
+ * @param reason why?
*/
@Override
- public void cancelPrefetches() {
+ public void cancelPrefetches(final CancelReason reason) {
+ LOG.debug("Cancelling prefetches {}", reason);
BlockOperations.Operation op = ops.cancelPrefetches();
- for (BufferData data : bufferPool.getAll()) {
- // We add blocks being prefetched to the local cache so that the
prefetch is not wasted.
- if (data.stateEqualsOneOf(BufferData.State.PREFETCHING,
BufferData.State.READY)) {
- requestCaching(data);
+ if (reason == CancelReason.RandomIO) {
+ for (BufferData data : bufferPool.getAll()) {
+ // We add blocks being prefetched to the local cache so that the
prefetch is not wasted.
+ // this only done if the reason is random IO-related, not due to
close/unbuffer
+ if (data.stateEqualsOneOf(BufferData.State.PREFETCHING,
BufferData.State.READY)) {
+ requestCaching(data);
+ }
}
+ } else {
+ // free the buffers
+ bufferPool.getAll().forEach(BufferData::setDone);
Review Comment:
we had so much grief with the abfs prefetch premature release bug that I am
scared now
> s3a prefetching stream to support unbuffer()
> --------------------------------------------
>
> Key: HADOOP-18184
> URL: https://issues.apache.org/jira/browse/HADOOP-18184
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Affects Versions: 3.4.0
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Priority: Minor
> Labels: pull-request-available
>
> Apache Impala uses unbuffer() to free up all client side resources held by a
> stream, so allowing it to have a map of available (path -> stream) objects,
> retained across queries.
> This saves on having to reopen the files, with the cost of HEAD checks etc.
> S3AInputStream just closes its http connection. here there is a lot more
> state to discard, but all memory and file storage must be freed.
> until this done, ITestS3AContractUnbuffer must skip when the prefetch stream
> is used.
> its notable that the other tests don't fail, even though the stream doesn't
> implement the interface; the graceful degradation handles that. it should
> fail if the test xml resource says the stream does it, but that the stream
> capabilities say it doesn't.
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