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https://issues.apache.org/jira/browse/HBASE-543?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12658626#action_12658626
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Jim Kellerman commented on HBASE-543:
-------------------------------------
@Stack:
> There is a bunch of redoing of state processing but no explanation
> as to why? For example:
>
{code}
+ * Remove a region from the region state map.
+ *
+ * @param info
+ */
+ public void removeRegion(HRegionInfo info) {
{code}
>
> Under what circumstance would I remove a region from state map?
>
> The region state map itself has no explanation:
>
{code}
+ // Needs to be SortedMap so we can specify a comparator
+ private final SortedMap<byte[], RegionState> regionState =
+ Collections.synchronizedSortedMap(
+ new TreeMap<byte[], RegionState>(Bytes.BYTES_COMPARATOR));
{code}
>
> The maps it would replace tried to explain what they were about.
> Nor does the new RegionState map.
Good points. The name of the map should really be regionsInTransition,
so removeRegion is called when a region completes the transitions from
unassigned -> assigned -> pending -> open
closing -> closed -> offline
closing -> closed -> unassigned -> assigned -> pending -> open
I will update the documentation and change the name of the map.
> With above said, looks like this could be an improvement in that
> state is all in one place.
Yes, it is no longer possible for a region to be in multiple states at
once as state transitions always clear all the other states.
> Should RegionState be looking for illegal states? It doesn't seem to
> do any checking. This would be a good place to check we're doing
> transitions properly.
Good point. It should at least check for valid state transitions to
make sure that they happen in the proper order. Will update to include
this.
> Should resetting of connection root region be done inside
> unsetRootRegion in below so the two actions are tied together:
>
{code}
+ master.connection.setRootRegionLocation(null);
+ master.regionManager.unsetRootRegion();
{code}
Yes. Good idea. The connection is visible inside this method.
> Does unsetRootRegion set root region to null in regionManger?
Yes.
> Maybe connection and regionManager both need an unsetRootRegion
> method (or both a setRootRegionLocation that takes null) so same
> action in two places uses similarily named methods (This stuff
> preexisted your patch).
Yes. I think connection should have an unsetRootRegion instead of
setRootRegion(null). setRootRegion should only take a valid
HServerAddress.
> In RegionState, data members are named isUnassigned, isClosing,
> etc. Usual javabean convention is that data members are named
> unassigned, closing, etc. and that isClosing is one of the names
> getters have.
Ok, no problem.
> Why dumpState and not toString?
No good reason. I was using it for debugging, and was going to remove
it, but having a toString is a good idea.
===
Making the above edits now. Do you want to re-review the patch when I'm done,
or should I commit?
> A region's state is kept in several places in the master opening the
> possibility for race conditions
> ----------------------------------------------------------------------------------------------------
>
> Key: HBASE-543
> URL: https://issues.apache.org/jira/browse/HBASE-543
> Project: Hadoop HBase
> Issue Type: Bug
> Components: master
> Affects Versions: 0.1.0, 0.1.1, 0.2.0
> Reporter: Jim Kellerman
> Assignee: Jim Kellerman
> Fix For: 0.19.0
>
> Attachments: 543.patch, 543.patch, recent-changes.patch,
> regionstate.txt
>
>
> A region's state exists in multiple maps in the RegionManager:
> unassignedRegions, pendingRegions, regionsToClose, closingRegions,
> regionsToDelete, etc.
> One of these race conditions was found in HBASE-534.
> For HBase-0.1.x, we should just patch the holes we find.
> The ultimate solution (which requires a lot of changes in HMaster) should be
> applied to HBase trunk.
> Proposed solution:
> Create a class that encapsulates a region's state and provide synchronized
> access to the class that validates state changes.
> There should be a single structure that holds regions in these transitional
> states and it should be a synchronized collection of some kind.
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