HConnectionManager.getConnection(HBaseConfiguration) returns new connection in
default HTable constructor
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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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