It is a bit more complex than that. It is actually a hash of some subset of the configuration properties. See HConnectionKey class if you want to learn more. But the important thing is that with the new style, you do not need to worry anything about these since there is no implicit connection sharing. Everything is explicit now.
Enis On Tue, Feb 17, 2015 at 11:50 PM, Serega Sheypak <[email protected]> wrote: > Hi, Enis Söztutar > You've wrote: > >>You are right that the constructor new HTable(Configuration, ..) will > share the underlying connection if same configuration object is used. > > What do it mean "the same"? is equality checked using reference (java == ) > or using equals(Object other) method? > > > 2015-02-18 7:34 GMT+03:00 Enis Söztutar <[email protected]>: > > > Hi, > > > > You are right that the constructor new HTable(Configuration, ..) will > share > > the underlying connection if same configuration object is used. > Connection > > is a heavy weight object, that holds the zookeeper connection, rpc > client, > > socket connections to multiple region servers, master, and the thread > pool, > > etc. You definitely do not want to create multiple connections per > process > > unless you know what you are doing. > > > > The model is changed, and the old way of HTable(Configuration, ..) is > > deprecated because, we want to make the Connection lifecycle management > > explicit. In the new model, an opened Connection is closed by the user > > again, and light weight Table instances are obtained from the Connection. > > Having HTable's share their connections implicitly makes reasoning about > it > > too hard. The new model should be pretty easy to follow. > > > > Enis > > > > On Sat, Feb 14, 2015 at 6:45 AM, Liu, Ming (HPIT-GADSC) < > [email protected]> > > wrote: > > > > > Hi, > > > > > > I am using HBase 0.98.6. > > > > > > I learned from this maillist before, that the recommended method to > > > 'connect' to HBase from client is to use HConnectionManager like this: > > > HConnection > > > con=HConnectionManager.createConnection(configuration); > > > HTableInterfacetable = > > > con.getTable("hbase_table1"); > > > Instead of > > > HTableInterface table = new > > > HTable(configuration, "hbase_table1"); > > > > > > I don't quite understand the reason. I was thinking that each time I > > > initialize a HTable instance, it needs to create a new HConnection. And > > > that is expensive. But using the first method, multiple HTable > instances > > > can share the same HConnection. That is quite reasonable to me. > > > However, I was reading from some articles on internet that , even if I > > use > > > the 'new HTable(conf, tbl)' method, if the 'conf' object is the same > one, > > > all the HTable instances will still share the same HConnection. I was > > > recently read yet another article and said when using 'new HTable(conf, > > > tbl)', one don't need to use the exactly same 'conf' object (same one > in > > > memory). if two 'conf' objects, two different objects are all the > same, I > > > mean all attributes of these two are same (for example, created from > the > > > same hbase-site.xml and never change) then HTable objects can still > share > > > the same HConnection. I also try to read the HTable src code, it is > very > > > hard, but it seems to me the last statement is correct: 'HTable will > > share > > > HConnection, if configuration is all the same'. > > > > > > Sorry for so verbose. My question: > > > If two 'configuration' objects are same, then two HTable object > > > instantiated with them respectively can still share the same > HConnection > > or > > > not? Directly using the 'new HTable()' method. > > > If the answer is 'yes', then why I still need the HConnectionManager to > > > create a shared connection? > > > I am talking about 0.98.6. > > > I googled for days, and even try to read HBase src code, but still get > > > really confused. I try to do some tests also, but since I am too > newbie, > > I > > > don't know how to verify the difference, I really don't know what a > > > HConnection do under the hood. I counted the ZooKeeper client requests, > > and > > > I found some difference. If this ZooKeeper requests difference is a > > correct > > > metrics, it means to me that two HTable do not share HConnetion even > > using > > > same 'configuration' in the constructor. So it confused me more and > > more.... > > > > > > Please someone kindly help me for this newbie question and thanks in > > > advance. > > > > > > Thanks, > > > Ming > > > > > > > > > > > >
