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From "Jack Chan" <cdj0...@gmail.com>
Subject why HTableDescriptor.getFamiliesKeys is so lag?
Date Thu, 17 Oct 2013 06:13:59 GMT
Hi all~
    I need to get all column families from specified table,When I look into the class "org.apache.hadoop.hbase.HTableDescriptor",I
found that 
there are more than three methods can be used.
    See the code below,there are method1,method2,method3 to do the same thing:

/*___________code begin___________*/

HTable table = new HTable(config, "mytable");
HTableDescriptor htd = table.getTableDescriptor();
//method 1
TimeCounter tc = new TimeCounter().run();
HColumnDescriptor[] cfs = htd.getColumnFamilies();
for(int i=0;i< cfs.length;i++){
    System.out.println("column family:"+new String(cfs[i].getName()));
System.out.println("time with getColumnFamilies-->"+tc.stop().getMicroSeconds());

TimeCounter tc2 = new TimeCounter().run();
Set<byte[]> family_keys = htd.getFamiliesKeys();
for(byte[] _f :family_keys){
    System.out.println("column family:"+new String(_f));
System.out.println("time with getFamiliesKeys-->"+tc2.stop().getMicroSeconds());

TimeCounter tc3 = new TimeCounter().run();
Collection<HColumnDescriptor> family_co = htd.getFamilies();
for(HColumnDescriptor family_co_entry :family_co){
    System.out.println("column family:"+new String(family_co_entry.getName()));
System.out.println("time with getFamilies-->"+tc3.stop().getMicroSeconds());

/*___________________code end_____________________*/

I found that the efficience of method 1 and method 3 are the same,about 120 us.
but the method2 is lagging,about 500us.

I just need to retieve the column families' names.So method2 is just meet my need.
but why is it so lag?


Jack Chan. 
A new Apache-Camel rider.
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