GitHub user tdas opened a pull request:
https://github.com/apache/spark/pull/2366
[SPARK-3495] Block replication fails continuously when the replication
target node is dead
If a block manager (say, A) wants to replicate a block and the node chosen
for replication (say, B) is dead, then the attempt to send the block to B
fails. However, this continues to fail indefinitely. Even if the driver learns
about the demise of the B, A continues to try replicating to B and failing
miserably.
The reason behind this bug is that A initially fetches a list of peers from
the driver (when B was active), but never updates it after B is dead. This
affects Spark Streaming as its receiver uses block replication.
The solution in this patch adds the following.
- Changed BlockManagerMaster to return all the peers of a block manager,
rather than the requested number.
- Refactored BlockManager's replication code to handle peer caching
correctly.
+ The peer for replication is randomly selected. This is different from
past behavior where for a node A, a node B was deterministically chosen for the
lifetime of the application.
+ If replication fails to one node, the peers are refetched.
+ The peer cached has a TTL of 1 second to enable discovery of new
peers and using them for replication.
- Added replication unit tests (replication was not tested till now, duh!)
This should not make a difference in performance of Spark workloads where
replication is not used.
@andrewor14 @JoshRosen
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/tdas/spark replication-fix
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/2366.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #2366
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commit af0c1daea8a22bca3b7826322205c887370ce247
Author: Tathagata Das <tathagata.das1...@gmail.com>
Date: 2014-09-11T02:54:31Z
Added replication unit tests to BlockManagerSuite
commit 9f0ac9fb20660ff183490d13f4e3195b9283bc61
Author: Tathagata Das <tathagata.das1...@gmail.com>
Date: 2014-09-11T08:44:18Z
Modified replication tests to fail on replication bug.
commit d081bf60e87689994a006603f84cb8f22ab19c6a
Author: Tathagata Das <tathagata.das1...@gmail.com>
Date: 2014-09-11T20:58:14Z
Fixed bug in get peers and unit tests to test get-peers and replication
under executor churn.
commit 03de02d532f51b23bc1b79fc76115aacbd64a4b1
Author: Tathagata Das <tathagata.das1...@gmail.com>
Date: 2014-09-12T00:46:02Z
Change replication logic to correctly refetch peers from master on failure
and on new worker addition.
commit 7598f913c52728f25b6bce91dd9ae6879105e261
Author: Tathagata Das <tathagata.das1...@gmail.com>
Date: 2014-09-12T00:52:16Z
Minor changes.
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