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https://issues.apache.org/jira/browse/HBASE-13814?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14599244#comment-14599244
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cuijianwei commented on HBASE-13814:
------------------------------------
Thanks for your concern [~lhofhansl] and sorry to reply late:). Yes,
master.getServerName() is not the correct server name serving the region and I
think we need to save the right region server name into znode in
AssignmentManager#unassign so that AssignmentManager#isCarryingRegion will get
the right result.
{quote}
I think we can simplify:
{code}
+ if (!regions.containsKey(region) || (serverName = regions.get(region))
== null) {
{code}
To
{code}
+ if ((serverName = regions.get(region)) == null) {
{code}
{quote}
Yes, it looks better, I will update the patch.
{quote}
Can we move:
{code}
+ ServerName serverName = null;
{code}
Inside the synchronized?
{quote}
Do you mean move it in the synchronized:
{code}
synchronized (this.regions) {
// Check if this region is currently assigned
if ((serverName = regions.get(region)) == null) {
...
{code}
However, the serverName will be used in another synchronized:
{code}
synchronized (regionsInTransition) {
state = regionsInTransition.get(encodedName);
synchronized (regionsInTransition) {
state = regionsInTransition.get(encodedName);
if (state == null) {
// Create the znode in CLOSING state
try {
versionOfClosingNode = ZKAssign.createNodeClosing(
master.getZooKeeper(), region, serverName); // ===> need to be used
here
{code}
so that the serverName is not visible if it is defined in the first
synchronized?
> AssignmentManager does not write the correct server name into Zookeeper when
> unassign region
> --------------------------------------------------------------------------------------------
>
> Key: HBASE-13814
> URL: https://issues.apache.org/jira/browse/HBASE-13814
> Project: HBase
> Issue Type: Bug
> Components: Region Assignment
> Affects Versions: 0.94.27
> Reporter: cuijianwei
> Priority: Minor
> Attachments: HBASE-13814-0.94-v1.patch
>
>
> When moving region, the region will firstly be unassigned from corresponding
> region server by the method AssignmentManager#unassign(). AssignmentManager
> will write the region info and the server name into Zookeeper by the
> following code:
> {code}
> versionOfClosingNode = ZKAssign.createNodeClosing(
> master.getZooKeeper(), region, master.getServerName());
> {code}
> It seems that the AssignmentManager misuses the master's name as the server
> name. If the ROOT region is being moved and the region server holding the
> ROOT region is just crashed. The Master will try to start a
> MetaServerShutdownHandler if the server is judged as holding meta region. The
> judgment will be done by the method AssignmentManager#isCarryingRegion, and
> the method will firstly check the server name in Zookeeper:
> {code}
> ServerName addressFromZK = (data != null && data.getOrigin() != null) ?
> data.getOrigin() : null;
> if (addressFromZK != null) {
> // if we get something from ZK, we will use the data
> boolean matchZK = (addressFromZK != null &&
> addressFromZK.equals(serverName));
> {code}
> The wrong server name from Zookeeper will make the server not be judged as
> holding the ROOT region. Then, the master will start a ServerShutdownHandler.
> Unlike MetaServerShutdownHandler, the ServerShutdownHandler won't assign ROOT
> region firstly, making the ROOT region won't be assigned forever. In our test
> environment, we encounter this problem when moving ROOT region and stopping
> the region server concurrently.
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