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https://issues.apache.org/jira/browse/HBASE-3962?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13047262#comment-13047262
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Philippe commented on HBASE-3962:
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Hi,
Thank you very much for your message. I did check the code source from the
latest release, but not of the trunk actually. It seems you covered all the
points I mentioned. Great !
However, I’m not really sure about a couple of things:
a) If I use the ‘same’ configuration each time I create a table, I’ll use the
same connection then. I have a server that connects to HBase. Isn’t there a
performance issue if the server will use only one connection to the quorum? As
the quorum allows me to MAX_CLIENT_CNXNS connections, should we use as many
connections as possible instead of just one for the same configuration?
b) The number of cached HConnection are now related to the number of
connections allowed by the zookeeper ensemble. But if I pass different
configuration, can’t they supposed to use different zookeeper quorum (I guess
that may be an extremely rare case)? If so, is there really a point to limit
the number of cached HConnections?
> HConnectionManager.getConnection(HBaseConfiguration) returns new connection
> in default HTable constructor
> ---------------------------------------------------------------------------------------------------------
>
> Key: HBASE-3962
> URL: https://issues.apache.org/jira/browse/HBASE-3962
> Project: HBase
> Issue Type: Bug
> Components: client
> Affects Versions: 0.90.1
> Reporter: Philippe
>
> The HBase instance are currently indexed by Configuration, which since
> HBASE-1976 does not have any other equivalence that the object equivalence.
> So, everytime a new configuration is passed to the method a new connection is
> created.
> If we create many HTable connections with the same configuration, there is no
> problem:
> HBaseConfiguration config = HBaseConfiguration.create();
> HTable table 1 = new HTable(config, "table1"); // init connection
> HTable table 2 = new HTable(config, "table2"); // re-use connection
> HTable table 3 = new HTable(config, "table3"); // re-use connection
> However, if we call the default constructor, or re-call
> HBaseConfiguration.create();, we will pass a new instance of the
> configuration to the constructor. This will cause many connections to be
> created:
> HTable table 1 = new HTable("table1"); // init connection
> HTable table 2 = new HTable("table2"); // init new connection
> HTable table 3 = new HTable("table3"); // init new connection
> I know connection should be pooled, but sometimes we have to create a new
> connection, and without having access to a previously instanced configuration
> object.
> Since zookeeper has a max client connection (default was 30, now is 10),
> after creating 30 instances of HTable, we can no longer access to the
> database.
> In addition to this, the HBASE_INSTANCES map does not close the connection
> when removing the eldest entry. So if we have a larger maxConnection value
> than the hard-coded MAX_CACHED_HBASE_INSTANCES variable, connections will
> remain but won't be closed. MAX_CACHED_HBASE_INSTANCES should actually be set
> from the hbase.zookeeper.property.maxClientCnxns parameter (value + 1).
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