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https://issues.apache.org/jira/browse/ACCUMULO-1243?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Keith Turner updated ACCUMULO-1243:
-----------------------------------
Fix Version/s: 1.4.4
> Multiple assignment may occur if tablet server dies during split
> ----------------------------------------------------------------
>
> Key: ACCUMULO-1243
> URL: https://issues.apache.org/jira/browse/ACCUMULO-1243
> Project: Accumulo
> Issue Type: Bug
> Affects Versions: 1.4.0
> Reporter: Keith Turner
> Priority: Critical
> Fix For: 1.5.0, 1.4.4
>
>
> Make the following change to the tablet server code. The tablet server has
> to die at this exact point for the bug to occur.
> {noformat}
> Index: src/main/java/org/apache/accumulo/server/tabletserver/Tablet.java
> ===================================================================
> --- src/main/java/org/apache/accumulo/server/tabletserver/Tablet.java
> (revision 1464780)
> +++ src/main/java/org/apache/accumulo/server/tabletserver/Tablet.java
> (working copy)
> @@ -3592,6 +3592,9 @@
> MetadataTable.splitTablet(high, extent.getPrevEndRow(), splitRatio,
> SecurityConstants.getSystemCredentials(), tabletServer.getLock());
> MetadataTable.addNewTablet(low, lowDirectory,
> tabletServer.getTabletSession(), lowDatafileSizes, bulkLoadedFiles,
> SecurityConstants.getSystemCredentials(), time, lastFlushID,
> lastCompactID, tabletServer.getLock());
> +
> + Runtime.getRuntime().halt(2);
> +
> MetadataTable.finishSplit(high, highDatafileSizes,
> highDatafilesToRemove, SecurityConstants.getSystemCredentials(),
> tabletServer.getLock());
>
> log.log(TLevel.TABLET_HIST, extent + " split " + low + " " + high);
> {noformat}
> Then create a table and add a split.
> {noformat}
> root@test15> createtable foo
> root@test15 foo> addsplits -t foo m
> {noformat}
> If there are multiple tablet servers, then its possible that multiple
> assignment may occur. Below is an example of this occurring after tablets
> were loaded.
> {noformat}
> root@test15 !METADATA> scan -b 1 -c loc
> 1;m loc:13d5a86463f4f98 [] 127.0.0.1:9998
> 1;m loc:13d5a86463f4f9f [] 127.0.0.1:10000
> 1< loc:13d5a86463f4f98 [] 127.0.0.1:9998
> {noformat}
> The problem is that the assignment code in the tserver detects an incomplete
> split and load both children. However, the master may also assign one of
> the children.
> I think the assignment code should be modified to fix up the metadata table
> and only load one tablet. If the new tablet was not created, it should roll
> back the changes and load the pre split tablets. If the new tablet was
> created, then assume the master will assign it and only load the high tablet.
> I think these changes would greatly simplify the code also.
> I do not think the proposed changes would cause issues with merge, since the
> chop flag is deleted in the case where this occurs.
> Need to ensure that the solution is itself fault tolerant.
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