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https://issues.apache.org/jira/browse/HDFS-15493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17167143#comment-17167143
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Stephen O'Donnell commented on HDFS-15493:
------------------------------------------
{quote}
I had tested loading the caches and blocks by two single thread executors, same
to your test result, there would be a long time to wait the executors
terminated, so the time cost was not better than the one executor with four
threads.
{quote}
Did you find the runtime was about the same with a single executor with 4
threads and two executors with a single thread? As my testing showed a small
improvement with the two single threaded executors case, and as locking
prevents more than one thread to run concurrently, I think it would be better
to go with the two executors with a single thread. This think the time required
for the executors to shutdown should be about the same in both cases.
I also made an earlier comment on this code:
{code}
if (blocksMapUpdateExecutor != null) {
blocksMapUpdateExecutor.shutdown();
Try {
while (!blocksMapUpdateExecutor.isTerminated()) {
blocksMapUpdateExecutor.awaitTermination(1, TimeUnit.MILLISECONDS);
}
} catch (InterruptedException e) {
LOG.error("Interrupted waiting for blocksMap update threads.", e);
throw new IOException(e);
}
}
{code}
I mis-understood how it worked, as I thought `awaitTermination(...)` threw an
exception after the timeout, which is not the case. However, I think it makes
sense to wait 500 or 1000ms rather than 1ms, and log a message indicating the
executor is not yet shutdown. Or, we could time how long it takes to shutdown
and log a message after the shutdown completes. That means we will get some
visibility into how long the executors take to catch up.
Also, for info, I ran my tests on trunk and the image also had some snapshots
which will have extended the load time.
> Update block map and name cache in parallel while loading fsimage.
> ------------------------------------------------------------------
>
> Key: HDFS-15493
> URL: https://issues.apache.org/jira/browse/HDFS-15493
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Reporter: Chengwei Wang
> Priority: Major
> Attachments: HDFS-15493.001.patch, fsimage-loading.log
>
>
> While loading INodeDirectorySection of fsimage, it will update name cache and
> block map after added inode file to inode directory. It would reduce time
> cost of fsimage loading to enable these steps run in parallel.
> In our test case, with patch HDFS-13694 and HDFS-14617, the time cost to load
> fsimage (220M files & 240M blocks) is 470s, with this patch , the time cost
> reduc to 410s.
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