[SPARK-17485] Prevent failed remote reads of cached blocks from failing entire job (branch-1.6 backport) #15186
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…ng entire job In Spark's `RDD.getOrCompute` we first try to read a local copy of a cached RDD block, then a remote copy, and only fall back to recomputing the block if no cached copy (local or remote) can be read. This logic works correctly in the case where no remote copies of the block exist, but if there _are_ remote copies and reads of those copies fail (due to network issues or internal Spark bugs) then the BlockManager will throw a `BlockFetchException` that will fail the task (and which could possibly fail the whole job if the read failures keep occurring). In the cases of TorrentBroadcast and task result fetching we really do want to fail the entire job in case no remote blocks can be fetched, but this logic is inappropriate for reads of cached RDD blocks because those can/should be recomputed in case cached blocks are unavailable. Therefore, I think that the `BlockManager.getRemoteBytes()` method should never throw on remote fetch errors and, instead, should handle failures by returning `None`. Block manager changes should be covered by modified tests in `BlockManagerSuite`: the old tests expected exceptions to be thrown on failed remote reads, while the modified tests now expect `None` to be returned from the `getRemote*` method. I also manually inspected all usages of `BlockManager.getRemoteValues()`, `getRemoteBytes()`, and `get()` to verify that they correctly pattern-match on the result and handle `None`. Note that these `None` branches are already exercised because the old `getRemoteBytes` returned `None` when no remote locations for the block could be found (which could occur if an executor died and its block manager de-registered with the master). Author: Josh Rosen <joshrosen@databricks.com> Closes apache#15037 from JoshRosen/SPARK-17485.
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Test build #65735 has finished for PR 15186 at commit
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srinathshankar
approved these changes
Sep 22, 2016
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Yep, 1.6 has fewer BlockManager tests. |
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Thanks for confirming, LGTM |
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I'm going to merge this into branch-1.6. Thanks! |
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…ng entire job (branch-1.6 backport) This patch is a branch-1.6 backport of #15037: ## What changes were proposed in this pull request? In Spark's `RDD.getOrCompute` we first try to read a local copy of a cached RDD block, then a remote copy, and only fall back to recomputing the block if no cached copy (local or remote) can be read. This logic works correctly in the case where no remote copies of the block exist, but if there _are_ remote copies and reads of those copies fail (due to network issues or internal Spark bugs) then the BlockManager will throw a `BlockFetchException` that will fail the task (and which could possibly fail the whole job if the read failures keep occurring). In the cases of TorrentBroadcast and task result fetching we really do want to fail the entire job in case no remote blocks can be fetched, but this logic is inappropriate for reads of cached RDD blocks because those can/should be recomputed in case cached blocks are unavailable. Therefore, I think that the `BlockManager.getRemoteBytes()` method should never throw on remote fetch errors and, instead, should handle failures by returning `None`. ## How was this patch tested? Block manager changes should be covered by modified tests in `BlockManagerSuite`: the old tests expected exceptions to be thrown on failed remote reads, while the modified tests now expect `None` to be returned from the `getRemote*` method. I also manually inspected all usages of `BlockManager.getRemoteValues()`, `getRemoteBytes()`, and `get()` to verify that they correctly pattern-match on the result and handle `None`. Note that these `None` branches are already exercised because the old `getRemoteBytes` returned `None` when no remote locations for the block could be found (which could occur if an executor died and its block manager de-registered with the master). Author: Josh Rosen <joshrosen@databricks.com> Closes #15186 from JoshRosen/SPARK-17485-branch-1.6-backport.
zzcclp
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Sep 23, 2016
…ng entire job (branch-1.6 backport) This patch is a branch-1.6 backport of apache#15037: ## What changes were proposed in this pull request? In Spark's `RDD.getOrCompute` we first try to read a local copy of a cached RDD block, then a remote copy, and only fall back to recomputing the block if no cached copy (local or remote) can be read. This logic works correctly in the case where no remote copies of the block exist, but if there _are_ remote copies and reads of those copies fail (due to network issues or internal Spark bugs) then the BlockManager will throw a `BlockFetchException` that will fail the task (and which could possibly fail the whole job if the read failures keep occurring). In the cases of TorrentBroadcast and task result fetching we really do want to fail the entire job in case no remote blocks can be fetched, but this logic is inappropriate for reads of cached RDD blocks because those can/should be recomputed in case cached blocks are unavailable. Therefore, I think that the `BlockManager.getRemoteBytes()` method should never throw on remote fetch errors and, instead, should handle failures by returning `None`. ## How was this patch tested? Block manager changes should be covered by modified tests in `BlockManagerSuite`: the old tests expected exceptions to be thrown on failed remote reads, while the modified tests now expect `None` to be returned from the `getRemote*` method. I also manually inspected all usages of `BlockManager.getRemoteValues()`, `getRemoteBytes()`, and `get()` to verify that they correctly pattern-match on the result and handle `None`. Note that these `None` branches are already exercised because the old `getRemoteBytes` returned `None` when no remote locations for the block could be found (which could occur if an executor died and its block manager de-registered with the master). Author: Josh Rosen <joshrosen@databricks.com> Closes apache#15186 from JoshRosen/SPARK-17485-branch-1.6-backport. (cherry picked from commit 94524ce)
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This patch is a branch-1.6 backport of #15037:
What changes were proposed in this pull request?
In Spark's
RDD.getOrComputewe first try to read a local copy of a cached RDD block, then a remote copy, and only fall back to recomputing the block if no cached copy (local or remote) can be read. This logic works correctly in the case where no remote copies of the block exist, but if there are remote copies and reads of those copies fail (due to network issues or internal Spark bugs) then the BlockManager will throw aBlockFetchExceptionthat will fail the task (and which could possibly fail the whole job if the read failures keep occurring).In the cases of TorrentBroadcast and task result fetching we really do want to fail the entire job in case no remote blocks can be fetched, but this logic is inappropriate for reads of cached RDD blocks because those can/should be recomputed in case cached blocks are unavailable.
Therefore, I think that the
BlockManager.getRemoteBytes()method should never throw on remote fetch errors and, instead, should handle failures by returningNone.How was this patch tested?
Block manager changes should be covered by modified tests in
BlockManagerSuite: the old tests expected exceptions to be thrown on failed remote reads, while the modified tests now expectNoneto be returned from thegetRemote*method.I also manually inspected all usages of
BlockManager.getRemoteValues(),getRemoteBytes(), andget()to verify that they correctly pattern-match on the result and handleNone. Note that theseNonebranches are already exercised because the oldgetRemoteBytesreturnedNonewhen no remote locations for the block could be found (which could occur if an executor died and its block manager de-registered with the master).