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https://issues.apache.org/jira/browse/HBASE-3766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13018591#comment-13018591
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Jean-Daniel Cryans commented on HBASE-3766:
-------------------------------------------
Ah I see, sorry I thought you were adding the reference counting in HCM, but I
see it's in HCI (which does make a lot more sense). That works yeah.
So two other things:
This is dangerous because you are closing the connections to all the regions
servers and the master, you want to pass false:
{quote}
+ HConnectionManager.deleteConnection(this.configuration, true);
{quote}
Then I'd like to see some unit testing.
Also I'm not sure we want this in 0.90.3, targeting 0.92 would be better.
> Manage Connections Through Reference Counts
> -------------------------------------------
>
> Key: HBASE-3766
> URL: https://issues.apache.org/jira/browse/HBASE-3766
> Project: HBase
> Issue Type: Improvement
> Components: client
> Affects Versions: 0.90.2
> Reporter: Karthick Sankarachary
> Assignee: Karthick Sankarachary
> Priority: Minor
> Fix For: 0.90.3
>
> Attachments: HBASE-3766.patch, HBASE-3766.patch
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> As of now, the onus is on the developer to explicitly close connections once
> they're done using them. Furthermore, since connections are managed based on
> the identity of the {{Configuration}} object, one is forced to clone the
> configuration object in order to be able to clean it up safely (for a case in
> point, see {{HTablePool's}} constructor). As a matter of fact, this issue has
> been well-documented in the HConnectionManager class:
> {quote}
> But sharing connections makes clean up of {{HConnection}} instances a little
> awkward. Currently, clients cleanup by calling
> {{#deleteConnection(Configuration, boolean)}}. This will shutdown the
> zookeeper connection the {{HConnection}} was using and clean up all
> {{HConnection}} resources as well as stopping proxies to servers out on the
> cluster. Not running the cleanup will not end the world; it'll just stall the
> closeup some and spew some zookeeper connection failed messages into the log.
> Running the cleanup on a {{HConnection}} that is subsequently used by
> another will cause breakage so be careful running cleanup. To create a
> {{HConnection}} that is not shared by others, you can create a new
> {{Configuration}} instance, pass this new instance to
> {{#getConnection(Configuration)}}, and then when done, close it up by doing
> something like the following:
> {code}
> Configuration newConfig = new Configuration(originalConf);
> HConnection connection = HConnectionManager.getConnection(newConfig);
> // Use the connection to your hearts' delight and then when done...
> HConnectionManager.deleteConnection(newConfig, true);
> {code}
> {quote}
> Here, we propose a reference-count based mechanism for managing connections
> that will allow {{HTables}} to clean up after themselves. In particular, we
> extend the {{HConnectionInterface}} interface so as to facilitate reference
> counting, where, typically, a reference indicates that it is being used by a
> {{HTable}}, although there could be other sources.
> To elaborate, when a HTable is constructed, it increments the reference count
> on the connection given to it. Similarly, when it is closed, that reference
> count is decremented. In the event there are no more references to that
> connection, {{HTable#close}} takes it upon itself to delete the connection,
> thereby sparing the developer from doing so.
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