[
https://issues.apache.org/jira/browse/HDFS-6735?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Lars Hofhansl updated HDFS-6735:
--------------------------------
Attachment: HDFS-6735-v4.txt
New patch:
* added synchronized back to tryZeroCopyRead
* renamed sharedLock to infoLock
* this time did all the correct indentation - harder to review, but this should
be committable as is
* surrounded every reference to cachingStrategy with synchronized(infoLock)
{...}, removed volatile
Looking at this again, we can be better about safe publishing with immutable
state and avoid some of the locks.
For example FileEncryptionInfo and CachingStrategy are already immutable and
can be 100% safely handled by just a volatile reference; most the LocatedBlocks
state is also immutable and for those parts we can avoid the locks as well.
Immutable state is easier to reason about and more efficient.
(volatile still places read and write memory fences - but that is cheaper than
synchronized). Can do that later :)
> A minor optimization to avoid pread() be blocked by read() inside the same
> DFSInputStream
> -----------------------------------------------------------------------------------------
>
> Key: HDFS-6735
> URL: https://issues.apache.org/jira/browse/HDFS-6735
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client
> Affects Versions: 3.0.0
> Reporter: Liang Xie
> Assignee: Liang Xie
> Attachments: HDFS-6735-v2.txt, HDFS-6735-v3.txt, HDFS-6735-v4.txt,
> HDFS-6735.txt
>
>
> In current DFSInputStream impl, there're a couple of coarser-grained locks in
> read/pread path, and it has became a HBase read latency pain point so far. In
> HDFS-6698, i made a minor patch against the first encourtered lock, around
> getFileLength, in deed, after reading code and testing, it shows still other
> locks we could improve.
> In this jira, i'll make a patch against other locks, and a simple test case
> to show the issue and the improved result.
> This is important for HBase application, since in current HFile read path, we
> issue all read()/pread() requests in the same DFSInputStream for one HFile.
> (Multi streams solution is another story i had a plan to do, but probably
> will take more time than i expected)
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
